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LL 05: Domestic air-to-air heat exchangers

AIVC, 2001
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Bibliographic info: LL 05
Languages: English

Domestic air-to-air heat exchangers


#NO 10029 Pressure and flow loss in natural ventilation stacks due to insertion of heat pipes for heat recovery.

Shao L, Riffat S B

Indoor Air '96, proceedings of the 7th International Conference on Indoor Air Quality and Climate, held July 21-26, 1996, Nagoya, Japan, Volume 1, pp 871-876.

Study of pressure and flow loss caused by heat-pipes for heat recovery was carried out using computational fluid dynamics. It has been shown that heat-pipes located in the bottom of the stack produce greater insertion flow loss (IFL) than those located at the top. In addition, heat-pipes located next to the stack walls give rise to less IFL than those places in the centre. The results also showed that a smaller insertion pressure (IPL) caused by a heat-pipe corresponds to a greater IFL and vice versa. It has been demonstrated that IFL is the preferred indicator for loss caused by obstacles submerged in stack flows. The temperature of the heat pipe has little effect on flow loss performance of the heat exchangers.

stack effect, natural ventilation, heat recovery

#NO 10274 Opportunities for improving the energy efficiency of window-type room air conditioners. 

Rosenquist G 

USA, Washington DC, American Council for an Energy Efficient Economy (ACEEE), Proceedings of the 1996 Summer Study on Energy Efficiency in Buildings, "Profiting from Energy Efficiency" 

As required by the National Appliance Energy Conservation Act (NAECA), minimum energy efficiency standards ranging from 8.0 to 9.0 EER went into effect for window-type room air conditioners on January 1, 1990. But by incorporating commonly used technologies such as high-efficiency rotary compressors, grooved refrigerant tubing, slit-type fins, subcoolers, and permanent split capacitor fan motors, 10.0 EER efficiency levels can be achieved for the most popular classes of room air conditioners without having to increase chassis size. Even greater efficiency increases can be realized with brushless permanent magnet fan motors, enlarged heat exchanger coils, and variable speed compressors. Efficiency increases were estimated through the use of a calibrated computer simulation model. To assess the cost-effectiveness of the above design options, their impact on manufacturing cost was estimated with data supplied by both room air conditioner manufacturers and component suppliers. New minimum efficiency standards set at levels requiring approximately a 10.0 EER for the most popular classes would result in the following projected benefits: (1) national energy savings of 0.69 Quads over the period 1999-2030, (2) SO2,NOx, and CO2 emission reductions of 111 kt, 104 kt, and 57 Mt, respectively, over the period 1999-2030, and (3) peak demand savings of 2.17 GW by the year 2025. For the consumer, a ``10.0 EER'' minimum standard yields the lowest life-cycle cost and the corresponding payback period is no greater than six years for the most popular classes. 

air conditioning, energy efficiency, standard, window


#NO 10462 Improved ventilation in existing single dwelling houses -installation, measurement and analysis in Ostersund and Kalix.Forbattrad ventilation i befintliga smahus. Installation, matning ochanalys Ostersund och Kalix.

Dahlberg L

Sweden, Swedish Council for Building Research, Report No A2:1996, 166pp.

The ventilation systems in 21 single dwelling houses in the north of Sweden have been modified to improve indoor climate and increase airflow rate without increasing energy use. In about half the houses control equipment was installed which reduces the speed of the extract fans when the outside temperature drops. Fresh air inlets were installed near windows in bedrooms and the living room. In the other houses a ventilation plant with inlet and extract terminals and a heat exchanger was installed. The modified ventilation systems have performed well technically, and in all system types the total specific fresh air flow rate has been increased. Greater investment in heat recovery does not however result in a corresponding reduction in energy costs. With present energy prices, energy use and modification costs, the least investment also produces the lowest total cost.

single family house, ventilation system, air flow rate, heat exchanger

#NO 10467 Benchmarks for better buildings.

Anon

UK, Building Services Journal, April 1997, pp 26-41.

Collection of short articles outlining the priorities for improving building design. These include a discussion of the benefits of post occupancy research in buildings, the prediction and eradication of faults such as valve leaks, sensor drift and fouled heat exchangers leading to higher energy consumption, and an account of the Probe research project, in which eight buildings were studied, focusing on the engineering and energy issues.

building design

#NO 10489 Experiences with solar air heating in Hungary.

Takacs L, Zold A

Japan, PLEA 1997 Kushiro Secretariat, proceedings of a conference held 8-10 January 1997, Kushiro, Japan, Volume 1, pp 75-80, 5 figs.

Pilot houses with solar air heating systems were and are being erected in Hungary by the "THERMO Ltd" Company. This project had two goals: to adapt the OM concept as a whole, including the thermal properties of the building itself, and to check the performance of the elements of the OM system applied on houses, built according to the local standards and practice are briefly presented in the paper. It has been proven that the OM roof collectors, handling box, heat exchanger of domestic hot water and intensified summer ventilation perform well under Hungarian climatic conditions, habitants are satisfied with thermal comfort and energy bill. On the other hand, it was shown that thermal insulation of building and quality of craftmanship should be improved, thermal mass and collector area better harmonised.

passive solar design, air heating, heat exchanger

#NO 10501 Dehumidification becomes important for a building having thick thermal insulation.

Shinagawa K, Aratani N, Taghi S M

Japan, PLEA 1997 Kushiro Secretariat, proceedings of a conference held 8-10 January 1997, Kushiro, Japan, Volume 2, pp 347-352, 8 figs, 3 tabs, 3 refs.

As the sensible heat gain or cooling load are decreased by using thick thermal insulation in a building, the need for dehumidification increases. Especially in Kushiro, it is rather cool and humid in summer because of its foggy weather. In this study, two types of dehumidification systems were developed and their performances were examined. The first is a heat-recovery type, which uses a cooling coil and a sensible heat exchanger. The second is a moisture-absorbent type, which uses heating and cooling coils and an absorbent. Remarkable improvements in dehumidification were obtained using the first type of dehumidification system. Using the second type of system, although the temperature of the outlet air rose slightly, both the absolute and relative humidity decreased remarkably. These features are desirable for a city such as Kushiro, in which the climate in summer does not necessitate much cooling of inlet air as is the function of an ordinary air conditioner. The moisture-absorbent type makes the most effective use of the cooling power for dehumidification of the three types. The result also showed that dehumidification is indispensable for thick thermal insulation, indicating that thick thermal insulation should be a key factor in passive and low energy architecture.

dehumidification, thermal insulation, heat recovery, heat exchanger

#NO 10592 A method for the economical optimisation of the design temperatures and the connecting flows of a cooling system.

Sarkomaa P

UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation and Cooling", 18th Annual Conference, held Athens, Greece, 23-26 September 1997, Volume 2, pp 437-444.

The planning parameters of a cooling system for ventilation, for example the vaporization and condensing temperatures, heat capacity flow rates, design temperatures and design temperature differences have a strong influence on the investment and operating costs. The target of this research is to find economically optimized design parameters by minimizing the present value of investment and the operating costs of the cooling system. The cooling system may have several series connected heat exchangers on the vaporization and condensing sides of the cooling machine. When the optimization is carried out, such factors as the price of electricity, maintenance costs, operating time, interest rate, annual running time, the coefficient of performance, marginal costs of heat transfer surface areas and the overall heat transfer coefficients of the vaporizer, the condenser and the other heat exchangers which are connected to the same system, are taken into account. This new method is useful for the economical optimization of the design parameters of ventilation and other cooling systems.

cooling, temperature

#NO 10601 Performance of series connected heat exchangers with liquid circuit on loop.

Marttila E

UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation and Cooling", 18th Annual Conference, held Athens, Greece, 23-26 September 1997, Volume 2, pp 535-546.

The series connected heat exchangers, configured either as an arrangement of gas-gas, gas-liquid or liquid-liquid heat exchangers, are widely used in the process industry and air-conditioning where they can be found in a variety of heat (cool) recovery, in heating and cooling applications. The design of heat exchangers follows the conventional design procedures for compact heat exchangers, and involves computation of exchanger dimensions to yield a prescribed heat exchanger efficiency and pressure drops for fluid streams. This paper describes a procedure for calculating the performance of series connected heat exchangers, when heat transfer fluid has been looped between heat exchangers. The heat exchanger system consists of heat (cool) recovery heat exchanger(s), pre-heater(s) or pre-cooler(s) and a main heat exchanger to heat or to cool a main stream to the aim temperature. The heat exchangers are connected with the looped fluid circuit. The connecting fluid flow rate has to be determined to achieve optimum heat or cool recovery. The following considerations has to be almost always made when the heat exchangers is designed for the application, * Heat transfer requirements * Costs * Physical size * Pressure drop characteristics In the main stream the heat transfer requirements for temperatures must be met in the selection or design of any heat exchanger. The way with which the requirements are met, depends on the relative weights placed on costs, physical size or pressure-drop characteristics. Economic plays a key role in the design and selection of heat exchanger equipment, and the engineer should bear this in mind when embarking on any new heat transfer design problem. For the used heat exchangers the presented procedure gives the looped fluid flow rate, with which the best possible heat recovery efficiency is achieved. In the other hand the procedure gives the performances for heat exchangers to achieve the end temperature of the main stream.

heat exchanger

#NO 10897 The influence of different ground covers on the heating potential of earth to air heat exchangers.

Mihalakakou G, Lewis J O, Santamouris M

UK, Renewable Energy, Vol 7, No 1, 1996, pp 33-46, 21 figs, 16 refs.

Ten years' hourly measurements of air and ground temperature values at various depths below the bare and short grass soil at Dublin airport have been used in order to investigate the impact of different ground surface boundary conditions on the efficiency of a single and multiple parallel earth-to-air heat exchanger system. The heating potential of both these systems buried under bare soil has been assessed and compared with the heating potential of the same systems buried under short-grass-covered soil. The results of this comparison revealed that soil surface cover might be a significant controllable factor for the improvement of the performance of earth-to-air exchanges. The heating system consists of a single pipe or multiple parallel pipes laid horizontally, through which ambient or indoor air is propelled and heated by the bulk temperature of the natural ground. The dynamic thermal performance of these systems during the winter period and their operational limits have been calculated using an accurate numerical model. Finally, a sensitivity analysis was performed in order to investigate the effect of the main design parameters, such as pipe length, pipe radius, air velocity inside the tube and the depth of the buried pipe below the earth's surface, on the system heating capacity. Cumulative frequency distributions of the air temperature at the pipe's exit have been developed as a function of the main input parameters. 

heat exchanger, temperature

#NO 10899 Use of buried pipes for energy conservation in cooling of agricultural greenhouses.

Santamouris M, Mihalakakou G, Balaras C A, Argiriou A, et al

USA, Solar Energy, Vol 55, No 2, 1995, pp 111-124, 6 figs, 1 tab, refs.

Earth-to-air heat exchanges can be used for energy conservation in cooling of agricultural greenhouses. A parametric analysis performed for a typical glass greenhouse illustrates the effect of pipe length, pipe diameter, and air velocity inside the pipes on the performance of the system. Measured data of indoor air temperature collected from a 1000m2 fiberglass covered greenhouse, equipped with four buried pipes, are compared with calculated data and are found to be in very good agreement. 

cooling, heat exchanger

#NO 10901 On the performance of buildings coupled with earth to air heat exchangers.

Santamouris M, Mihalakakou G, Argiriou A, Asimakopoulos D N

USA, Solar Energy, Vol 54, No 6, 1995, pp 375-380, 2 figs, 2 tabs, refs.

The use of earth to air exchangers has gained an increasing acceptance during the recent years. However, there is a lack of circulation models coupling the performance of the exchangers with the building. The present paper deals with the development of a new integrated model to calculate the contribution of the earth to air heat exchangers to reduce the cooling load of buildings. The method is based on the principle of balance point temperature and permits the calculation of the hourly value of the balance temperature of the building as well as the daily cooling load of the building and the contribution of the buried pipes. An extensive validation procedure has been followed using data from an extended version of TRNSYS including detailed routines to simulate dynamically the performance of earth to air heat exchangers. It is found that the method is of sufficient accuracy and, therefore, can be used during the predesign and design phase for the dimensioning of the buried pipes. 

heat exchanger, building performance

#NO 10902 Parametric prediction of the buried pipes cooling potential for passive cooling applications.

Mihalakakou G, Santamouris M, Asimakopoulos D, Tselepidaki I

USA, Solar Energy, Vol 55, No 3, 1995, pp 163-173, 2 figs, 3 tabs, refs.

A new parametrical model for the prediction of the thermal performance of the earth to air heat exchangers is presented. The system consists of an earth tube, buried in the ground through which ambient heat or indoor air is propelled and cooled by the bulk temperature of the natural ground. The proposed model has been developed by analysing temperature data of the circulated air at the pipe's outlet using a systematic parametrical process. Four variables influencing the thermal performance of the earth to air heat exchangers were taken into account: pipe length (L), pipe radius (r), velocity of the air inside the tube (V) and depth of the buried pipe below the earth surface (D). The developed algorithm is suitable for the calculation of the exit air temperature, and therefore of the cooling potential of the system. The model was validated against experimental data as well as a data set which was obtained by an accurate numerical model describing the thermal performance of the earth tube system. 

passive cooling, modelling, thermal performance, heat exchanger

#NO 10903 Impact of ground cover on the efficiencies of earth to air heat exchangers.

Mihalakakou G, Santamouris M, Asimakopoulos, Papanikolaou N

UK, Applied Energy, No 48, 1994, pp 19-32, 11 figs, 11 refs.

The influence of different ground surface boundary conditions on the efficiency of a single earth-to-air heat exchanger as well as of a multiple parallel earth tubes system has been investigated. The cooling potential of both these systems buried under bare soil has been assessed and compared with the cooling potential of the same system buried under short-grass covered soil. The results revealed that soil surface could be a controllable factor for the improvement of the performance of earth-to-air heat exchangers. The cooling system consists of a single tube or multiple tubes, buried in the ground and through which ambient or indoor air is circulated and cooled; it is then mixed with the indoor air of a building or an agricultural greenhouse. An accurate numerical model has been used to assess the dynamic thermal performances and operational limits of the earth-to-air heat exchangers. Finally, a sensitivity investigation was carried out in order to evaluate the effect of the main design parameters of the air temperature at the pipe's exit have been developed as a function of the input parameters. 

heat exchanger, cooling

#NO 10904 On the cooling potential of earth to air heat exchangers.

Mihalakakou G, Santamouris M, Asimakopoulos D

UK, Energy Convers. Mgmt, Vol 35, No 5, 1994, pp 395-402, 5 figs, 20 refs.

The present paper deals with the cooling potential of earth to air heat exchangers. The cooling system consist of an underground pipe laid horizontally where ambient or indoor air is propelled through and cooled by the bulk temperature of the natural ground. The dynamic thermal performance of the system during the summer period and its operational limits have been calculated using an accurate transient numerical model. Multilayer soil and ambient air climatic measurements have been used as inputs to the model. An extensive sensitivity investigation has been performed in order to analyze the impact of the main design parameters on the cooling potential of the system. Cumulative frequency distributions of the exchanger's performance have been developed as a function of all the input parameters. The present paper aims to simplify the procedure for accurate design and performance evaluation of earth to air heat exchangers and to provide information on their cooling potential. 

passive cooling, earth to air heat exchangers, cooling potential, energy performance of buildings

#NO 10905 Modelling the thermal performance of earth to air heat exchangers.

Mihalakakou G, Santamouris M, Asimakopoulos D

USA, Solar Energy, Vol 53, No 3, 1994, pp 301-305, 6 figs, 22 refs.

A new complete numerical model for the prediction of thermal performance of the earth-to-air heat exchangers is presented. The model describes the simultaneous heat and mass transfer inside the tube and into the soil accounting for the soil natural thermal stratification. The model is validated against an extensive set of experimental data and it is found accurate. The proposed algorithms are suitable for the calculation of the temperature and humidity variation of the circulating air and for the temperature and humidity distribution inside the ground. The represented model was developed within the TRNSYS environment and can be easily coupled with building or greenhouse simulation codes in order to describe the impact of the earth to air heat exchangers to indoor environments. 

thermal performance, heat exchanger

#NO 10906 On the use of the atmospheric heat sinks for heat dissipation.

Agas G, Matsaggos T, Santamouris M, Argyriou A

UK, Energy and Buildings, No 17, 1991, pp 321-329, 7 figs, 22 refs.

During recent years, energy consumption of buildings for cooling purposes has significantly increased. In order to reduce the energy consumption while maintaining high levels of thermal comfort, building research has been oriented towards the appropriate use of the natural heat sinks. The present paper provides comparative information regarding the performance of the more important passive and hybrid cooling techniques involving the use of a natural heat sink. Ground cooling by the earth-to-air heat exchangers, direct and indirect evaporative coolers as well as night ventilation techniques are considered. The impact of the systems and techniques on the thermal behaviour of a typical building is investigated by means of a sensitivity analysis of the main parameters determining their performance. 

cooling, thermal comfort, heat exchanger

#NO 10910 Using earth to air heat exchangers for space cooling.

Mihalakakou G, Santamouris M, Asimakopoulos D

Clima 2000 Conference, November 1993, paper 74, 9pp.

This paper deals with the thermal performance of an earth to air heat exchanger for cooling and heating purposes. The cooling system consists of an earth tube buried in the ground through which ambient air is propelled and cooled by the bulk temperature of the natural ground. Fresh or indoor air can be circulated inside the tube. A new, more accurate, transient, implicit, numerical model based on the coupled and simultaneous transfer of heat and mass into the soil and the pipe has been developed. The proposed model was validated against experimental data and it was found that predicts accurately the temperature of the air along the tube and the temperature distribution of the ground at any point in the pipe vicinity. 

heat exchanger, cooling

#NO 10916 Dynamic simulation of central chilling system of a large office building.

Wang S, Wang J, Burnett J

Belgium, Proceedings of Clima 2000 Conference, held Brussels, August 30th to September 2nd 1997, paper 5, 21pp, 13 figs, 1 tab, 8 refs.

Dynamic simulation of a seawater-cooled chilling system is performed by using the dynamic models of centrifugal chillers, heat exchangers, seawater and chilled water networks, cooling coil, actuator, sensor, variable-speed pump and DDC controller of BEMS. The on-line control strategies for the central chilling system are tested and evaluated by using them to control the living chilling system under different AHU dynamic loads in four seasons. This paper presents the models developed to simulate the dynamic system, the on-line control strategies developed for the chilling system and the evaluation of the strategies by system dynamic simulation. 

cooling, ceiling, office building

#NO 10939 Indirect evaporative cooling of low energy building.

Arkar C, Medved S, Novak P

Belgium, Proceedings of Clima 2000 Conference, held Brussels, August 30th to September 2nd 1997, paper 243, 5 figs, 2 tabs, 7 refs.

With the growth of living standards, there is an increasing demand for the cooling of living space. Rational energy use demands the use of alternative ways of cooling because the energy consumption of compressor cooling is high. In this article a new cheap and efficient paperboard compact heat exchanger and indirect evaporative cooling are presented. Indirect evaporative cooling is the most suitable way of cooling for low energy buildings especially if combined with heat recovery ventilation system. Operation simulation of an indirect evaporative cooler installed in a low energy house is also shown. 

passive cooling, low energy buildings

#NO 10971 Exploiting the fabric.

Mulligan H

UK, Architects' J., Vol 206, No 5, 1997, pp 56-57.

Introduces the concept of dynamic insulation, in which the whole building fabric acts as a heat exchanger, which can cut energy use and improve ventilation of small buildings. Conduction heat loss through the external skin of a building is reduced by drawing ventilation air through porous insulation material, rather than through conventional openings such as windows and doors. By doing so, heat energy that would normally be lost by conduction to the outside of the building is returned to the inside via the incoming ventilation air. The ventilation air leaves the building by means of a fan/heat exchanger system where the heat energy in the outgoing ventilation air is extracted for re-use. This can be used to pre-heat incoming ventilation air through the insulation or to pre-heat cold water for the hot water system. In this way the overall energy consumption of the building can be reduced. Describes UK current and earlier research.

dynamic insulation, heat exchanger, thermal mass

#NO 10992 Air heating systems for low energy buildings.

Halozan H, Rieberer R

Netherlands, IEA Heat Pump Centre Newsletter, Vol 15, No 4, 1997, pp 21-22, 4 figs, refs.

Describes the situation in Austria regarding the recent improvements in the thermal insulation standard for buildings. Heat transmission values have been reduced to 0.35 W/m2K for walls, 1.4 W/m2K for windows, 0.25 W/m2K for ceilings, and 0.5 W/m2K for the basement floor. For single family houses with heated areas of 130-180 m2, this results in a specific heat load of approximately 60 W/m2. With a ground-coupled heat pump - in Austria usually a direct-evaporation unit - in combination with a low-temperature floor heating system using supply temperatures below 35oC, a seasonal performance factor (SPF) of 4 or even higher can be achieved. Concludes that air heating systems based on the controlled ventilation system with heat recovery via a heat exchanger and a heat pump seem to be the future solution for low-energy buildings. The high thermal insulation standard and controlled ventilation system provide excellent air quality, as well as high comfort levels for the consumer and a low energy bill.

low energy building, insulation, standard, heat pump

#NO 10996 Energy conservation in hotels using an air recycling system.

CADDET

Netherlands, CADDET Energy Efficiency, Result 281, March 1997, 4pp, 1 fig, 1 tab.

As an alternative to a conventional ventilation system with a plate heat exchanger, a leading hotel in Switzerland has installed a so-called "recirculation" ventilation system. The main feature is the recirculation of return air, with the resulting mixed air processed using fine particle, electrostatic and activated carbon filters. The heating energy required to heat the outdoor air in recirculation ventilation systems is zero. Savings in cooling energy compared to a conventional system are 10%, while savings in electricity consumption are 7-20%. The system is not only suitable for hotels, but also for a wide range of additional applications.

hotel, energy conservation, recirculation

#NO 11078 A testing and HVAC design methodology for air to air heat pipe heat exchangers.

Guo P, Ciepliski D L, Besant R W

HVAC&R Research, Vol 4, No 1, January 1998, pp 4-26, , 1998, 26pp, 16 figs, refs.

Air-to-air heat pipe exchangers were tested using ASHRAE Standard 84-1991 as a guide. Some changes are introduced for the test facility and methods of calculating effectiveness. ASNE PTC 19.1-1985 is used as a guide for uncertainty analysis. Tests were done for a range of mass flux [1.574 to 2.912 kg/(m2.s)], ratios of mass flow rates (0.6 to 1.85), supply air temperatures (-10oC to 40oC), and heat exchanger tilt angles (-8.9o to 11.2o). Because humidity changes in the exhaust and supply air streams were negligible, only the effectiveness of sensible and of total energy, and uncertainties with each independent variable. For balanced exhaust and supply flow rates at -10oC supply air temperature and 1.574 kg/(m2.s) mass flux, the measured effectiveness for sensible and total energy was calculated to be 0.48 and .044 respectively, with uncertainties of 0.057 and 0.052. These measurements decreased to 0.42 and 0.37, with uncertainties if 0.016 and 0.018 fir a mass flux of 2.912 kg/(m2.s). Because water vapor condensation effects were small or negligible, the difference between the effectiveness for the sensible and total energy was within the overlapping uncertainty range of each. Based on counterflow heat exchanger theory and convective heat transfer equations, expressions are presented to extrapolate the effectiveness data between and beyond the measures data points. These effectiveness equations, which represent the variation in effectiveness with several independent operating variables, are used for HVAC design that is aimed at achieving minimum life-cycle costs.

heat exchanger, air conditioning

#NO 11132 Natural ventilation with heat recovery using heat pipes.

Riffat S B, Shao L, Gan G

UK, Chartered Institution of Building Services Engineers, 1997, proceedings of CIBSE National Conference held Alexandra Palace, London, UK, 5-7 October 1997, Volume 2, pp 253-260, 4 figs, 4 refs.

Natural ventilation based on passive stacks is currently designed without incorporating heat recovery leading to wasteful heat loss. Heat recovery is not used because the pressure loss caused by conventional heat exchangers is large and could cause the ventilation system to fail. This paper presents laboratory investigation and computer simulation of a low pressure-loss heat recovery device for passive stack systems. It was found that the heat recovery effectiveness decreases with increasing stack velocity and heat recovery effectiveness of over 50% has been obtained in the experiments. It was also demonstrated that acceptable pressure losses can be achieved if the stack mean velocity is kept under approximately 1 m/s.

natural ventilation, heat recovery

#NO 11164 Recovery of heat from the exhaust air. Varmeatervinning ur franluft.

Isaksson A

Sweden, Vattenfall Utveckling AB, 1996, 21pp, 1 fig, 3 tabs, 11 refs.

Preventing ventilation losses in a house with extract ventilation is expensive if only the economic aspects are considered. But if an investment is to be made in buying a heat exchanger unit, consideration must also be given to factors such as better air quality, more uniform air temperature and energy use which benefits the environment. The publication shows what action and technology are available for the recovery of heat from exhaust air in single family houses.

heat recovery, heat losses, heat exchanger

#NO 11208 On modeling of heat exchangers in Modelica.

Mattsson S E

Society for Computer Simulation International, 1997, Proceedings of "Simulation in Industry: 9th European Simulation Symposium", a conference held Passau, Germany, October 19-22, 1997, pp 127-133, 4 figs, refs.

It is demonstrated how Modelica(TM) is used in a application to develop models that are useful when solving real problems. Modelica is a new unified modeling language being developed in an international effort to promote object-oriented and non-causal modeling, and exchange of model libraries. The application is a heat exchanger where the media are liquids, typically water. This type of heat exchangers can be used for district heating of houses and for production of hot tap water. The model developed illustrates very nicely the power of Modelica. The modularization concepts support flexible model components which are easy to use and to adapt when making a model of a real system with heat exchangers. The concept of class parameters support medium parameterization and arrays of model components support discretization. The expressive power of Modelica allows complete listing so the developed model components to be given. The model produces simulation results that agree very well with measured data.

heat exchanger, modelling

#NO 11209 Evaluation of a distributed parameter model for counterflow heat exchangers.

Laszczyk P

Society for Computer Simulation International, 1997, Proceedings of "Simulation in Industry: 9th European Simulation Symposium", a conference held Passau, Germany, October 19-22, 1997, pp 694-696, 4 figs, refs.

The paper deals with simulation of the heat exchanger and model evaluation. There are presented partial differential equations of heat exchanger model, which assume liquid mediums. Presented, in the paper, model is used as an approximation for three different type heat exchangers. The purpose of these investigations was to explain whether the same model could match well to different of shape and type exchangers by adjusting some model parameters. There is show a method of determining model parameters. Results of simulation are compared with measured data.

heat exchanger, modelling, evaluation

#NO 11335 Heat recovery in passive stack ventilation using heat pipes.

Shao L, Riffat S B, Gan G

The Canadian Environment Industry Association (CEIA), 1997, proceedings of the 5th International Symposium on Ventilation for Contaminant Control, held in Ottawa, Ontario, Canada, September 14-17, 1997, Volume 2, pp 723-733, 6 figs, 1 tab.

Passive-stack ventilation (PSV) systems are currently designed without incorporating heat recovery leading to wasteful heat loss. It has been estimated that this heat loss amounts to 3 - 15 GJ per annum for a small family residence and much more for larger buildings. Heat recovery is not used because the pressure loss caused by conventional heat exchangers is large and could cause the ventilation system to fail. This work is concerned with an experimental and computational study of a low pressure-loss heat recovery device based on heat pipes. Heat recovery effectiveness of over 50% has been achieved in laboratory experiments. It has also found that the effectiveness decreases with increasing air velocity. The heat recovery is between 16% and 17% more efficient using two banks of heat pipes than using one bank. The stack mean velocity should be kept under 1 m/s in order to achieve acceptable pressure losses.

passive stack ventilation, heat pipe, heat recovery

#NO 11416 Combustion venting training course: student manual.

Geddes Enterprises

Canada Mortgage and Housing Corporation, January 1991.

Manual provides heating service technicians with the most up-to-date information available on the venting of the products of combustion of conventional (naturally aspirated) gas and oil fired appliances. It is intended for use both as a student text and as a reference manual. It describes the proper operation of a chimney and the symptoms of spillage of combustion products. The authors have included checklists that can be used to determine whether a venting problem exists. It also provides test procedures for the service technician to evaluate a combustion venting system and to detect a leaking heat exchanger. Remedial measures to solve problems once they have been detected are also discussed in some detail. 

combustion appliance, ventilation strategy, stack effect, wind effect

#NO 11430 Northern ventilation project: data collection and report for Iqaluit, N. W. T.

Ferguson, Simek, Clark Engineers & Architects

Canada Mortgage and Housing Corporation, November 1988.

In the high Arctic environment, whiteouts and snow laden winds are a common occurrence. The purpose of the Iqaluit project is to test the performance of several air-to-air heat exchangers from different manufacturers under such conditions. The Iqaluit installation was a typical example of the problems faced in such cold climates. The structure had moisture problems and very high humidity levels during the first winter. The heat exchangers were installed with the objective of understanding whether the air-to-air exchangers would keep the humidity levels reasonable regardless of other problems which could be encountered with respect to snow drifting and frosting. The project's intent is to observe the HRVs in an actual operating environment with emphasis placed on how the exchanger behaves in relation to the environment over an extended period. The housing units are situated above the treeline in high wind and driven snow. Report concludes that all HRVs currently manufactured and tested under this project deteriorate in performance beyond -20 Deg Celsius. Identifies work needed to develop separation of snow particles in a self cleaning fashion. Concludes that HRVs in a high Arctic environment do reduce the levels of relative humidity in dwellings, regardless of the operational problems.

cold climate, air to air heat exchanger, moisture, humidity, heat recovery ventilator

#NO 11482 Ventilative Strategies for Low-Income Dwellings

Mosconi P, Elicabe Urriol J, Di Bernardo E

Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 37-44.

Passive cooling devices for low-cost housing, where thermal comfort is usually not considered as an important variable of the design process are evaluated. Low-cost dwellings, located in Rosario city, Argentina, with temperate-humid climate are presented. Their design is the result of the interaction of occupants' participation and experts' advice. Passive cooling systems' efficiency for this climate is very low, due to the combination of high air temperatures and vapour pressure, which reduce convective cooling efficiency. An alternative to ameliorate summer conditions could be to enhance airflow patterns through natural ventilation. A sequence of diurnal and nocturnal ventilative strategies is proposed to achieve thermal comfort. Two ventilative systems have been installed: a duct located at the ridge of a pitched roof and an underground air-heat exchanger buried at depth foundations. Both are to operate depending on climate conditions. Results of systems performance are compared with theoretical considerations.

low income housing, ventilation strategy, passive cooling

#NO 11496 Perceived Air Quality: Should We Use a Linear or a Nonlinear Scale for the Relation between Odour Intensity and Concentration?

Fitzner K

Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 149-154.

Assessing the perceived air quality in decipols by trained panels can be performed rather perfectly today. To calculate the olf load from these results is a little more problematic as one requires olf loads which can simply be added (linearly). The reason for this difficulty is the nonlinear relation between the perceived air quality in decipol and the pollution load in olf. The relation can be expressed by an exponential function in a range between 1 to 15 decipols. Unfortunately the exponent and the constant in the exponential function differ for different substances. For the most substances they can fairly well be approached by a root law. This is shown for three very different examples: the required outdoor air flow for ventilated rooms with different outdoor air qualities, the exponential law for linoleum and the balance of pollution of a rotary heat exchanger.

odour, indoor air quality, outdoor air

#NO 11558 Evaluation of thermal performances of residential ventilation systems with heat recovery.

Bernard A M, Lemaire M C, Spennato B

UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation Technologies in Urban Areas", 19th Annual Conference, held Oslo, Norway, 28-30 September 1998, pp 242-251.

Ventilation systems with heat recovery offer several advantages such as, of course, energy savings but also the possibility to add acoustic and filtration treatment. This study was to evaluate the thermal performances of such systems for residential ventilation in France. These units usually combine exhaust and supply fans, filters and a heat recovery exchanger. To test them, a special draft is being written by the CEN experts of TC 156/WG/AH7. The study included the test of several units according to this project to evaluate their performances: temperature ratios, airflow/pressure curves, electric power, internal and casing leakages... The influence of humidity, condensation, frost and several full duct-systems simulating a standard house equipment have also been tested.

thermal performance, heat recovery

#NO 11615 Measurement and simulation of air flow in a two-zone chamber with heat-pipe heat recovery.

Gan G, Riffat S B

International Journal of Ambient Energy, Volume 19, No 2, April 1998, pp 93-103, 7 figs, 15 refs.

The performance of a heat-pipe heat recovery unit was tested in a two-zone chamber with a horizontal partition. Air velocity was found to have a significant effect on the effectiveness of heat recovery. The effectiveness decreased with increasing air velocity.

Simulation of air flow was carried out for the test chamber under natural ventilation conditions. It was shown that a heat-pipe exchanger can be used to reclaim exhaust in naturally-ventilated buildings to effect energy conservation.

heat recovery, energy efficiency

#NO 11726 Heat recovery with low pressure loss for natural ventilation.

Shao L, Riffat S B, Gan G

UK, Energy and Buildings, No 28, 1998, pp 179-184, 11 figs, 1 tab, 4 refs.

Heat recovery is difficult to implement in passive stack ventilation because the pressure loss is usually too high in conventional heat exchangers compared with the stack pressure. Laboratory investigation and computer simulation have been carried out on a low pressure-loss heat recovery device based on heat pipes which is suitable for application in passive stack systems and other systems where a low pressure loss is essential. It was found that heat recovery efficiency decreased with increasing air velocity. Heat recovery efficiency of close to 50% have been achieved using a single-bank plain-fin unit and the efficiency of a double bank unit was 40% higher than that of a single bank unit. It was also found that the pressure loss coefficient reduces as velocity increases but the reduction is around 10% over the entire range of common velocities in natural ventilation systems. The pressure loss across the plain fin unit is in the order of 1 Pa at a flow velocity of 1 m/s. The wire fin and plain fin type heat-pipe units are superior to other types investigated in this study.

heat recovery

#NO 11861 Performance of heat recovery in passive stack ventilation systems.

Shao L, Riffat S B, Gan G

UK, Chartered Institution of Building Services Engineers (CIBSE), 1998, Proceedings of "Harnessing technology for sustainable development", CIBSE National Conference '98, held Bournemouth International Conference Centre, 18-20 October 1998, pp 174-181, 4 figs, 1 tab, 5 refs.

The large heat loss from Passive-stack ventilation (PSV) systems quite often makes natural ventilation systems unattractive and it is therefore desirable to implement heat recovery in PSV stacks. As the stack pressure is usually about a few Pascal, it is crucial that the heat recovery unit used in a PSV system produces an even lower pressure loss, which is extremely difficult to achieve with the conventional plate heat exchangers. This work is concerned with a low pressure-loss heat recovery device based on heat pipes. The heat pipe is a completely passive device without power consumption and its simple construction also means that it also has a low initial cost. Experimental investigation has been carried out using four types of heat pipe heat exchangers. Heat recovery efficiency of over 60% has been obtained using two banks of exchangers. It was also found that the efficiency decreases with the increasing air velocity. Spine fin exchangers proved much lower efficiency than plain fin systems. Louver fined system produced the greatest efficiency but also the largest pressure loss. The wire-fin type produced a lower pressure loss than the plain fin type although its effieiency was also slightly lower. It was concluded that the wire fin type provided the optimum balance between the requirements for low pressure loss and high efficiency.

heat recovery, passive stack ventilation, heat exchanger

#NO 11872 Contaminant and heat removal effectiveness and air-to-air heat/energy recovery for a contaminated air space.

Irwin D R, Simonson C J, Saw K Y, Besant R W

USA, ASHRAE, 1998, in: the ASHRAE Transactions CD, proceedings of the 1998 ASHRAE Annual Meeting, held Toronto, Canada, June 1998, 15 pp, 12 figs, refs.

Measured contaminant and heat removal effectiveness data are presented and compared for a 3:1 scale model room, which represents a smoking room, lounge, or bar with a two dimensional airflow pattern. In the experiments, heat and tracer gases were introduced simultaneously from a source to simulate a prototype smoking room. High-side-wall and displacement ventilation schemes were investigated, and the latter employed two different types of ceiling diffuser; low-velocity slot and low-velocity grille.

Results show that thermal energy removal effectiveness closely follows contaminant removal effectiveness for each of the ventilation schemes throughout a wide range of operating conditions. The average mean thermal and contaminant removal effectiveness agreed within +/-20%. Local contaminant removal effectiveness ranged from a low of 80% for a high-wall slot diffuser to more than 200% for a low-velocity ceiling diffuser with displacement ventilation. Temperature differences between the supply and the indoor air were between 0.2 Deg.C (0.36 Deg.F) and 41.0 Deg.C (73.8 Deg.F) and ventilation airflow rates ranged from 9.2 to 36.8 air changes per hour at inlet conditions,. For small temperature differences between supply and exhaust air, all three ventilation schemes showed increased contaminant removal effectiveness near the supply diffuser inlets with decreasing values toward the exhaust outlet. For the high-side-wall slot diffuser, effectiveness was up to 140% near the in less and 100% near the exhaust, but for the second displacement scheme (low-velocity grille) the effectiveness was more than 200% near the inlet and 110% near the exhaust.

This paper also shows a potential significant reduction in cooling load for a 50-person-capacity smoking lounge that utilizes an air-to-air heat/energy exchanger to recover heat/energy from the exhaust air.

heat recovery, ventilation effectiveness, displacement ventilation

#NO 12064 Analysis of thermal sensation in a radiant cooled room by modified PMV index.

Miyanaga T, Nakano Y

Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 125-131, 8 figs, 4 tabs.

The objective of this study is to develop a method for analysing the thermal environment and the thermal sensation in the radiant cooled room.

In this paper, detailed three-dimensional models of the room and the indoor occupant were constructed and the steady-state thermal environment was analysed by the conjugate heat transfer analysis of thermal radiation and convection. The modified PMV index was proposed to evaluate the thermal sensation of the occupant in the asymmetrical thermal radiant environment such as the radiant cooled room. The modified PMV index was simply introduced by replacing the heat exchange by convection and radiation around the real human body, which approximately calculated in the Fanger's equations for the PMV index, with the analysed results around the body surface model.

The analysed values of air temperature and wall temperature distributions in the room were in good agreement with the measured values. The modified PMV index was closer to the actual thermal sensation by real subjects than PMV indices. The validity of the analysis method and models used were examined.

heat transfer, occupant reaction, thermal performance

#NO 12067 Integral simulation of the human thermal system.

Conceicao E Z E

Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 151-158, 8 figs, refs.

In this work a numerical model that permits to simulate the human body thermal system is presented.

This computational model is based on the integral energy balance equation for the human body tissue, arterial and venous blood and mass balance equation for the blood. In the simulation of the human body, which is divided in 105 nodes, the following phenomena are considered: heat conduction through the tissue, heat exchange by radiation between the external tissue and the surrounding surface, internal metabolism, heat loss by evaporation and respiration, blood circulatory convection and heat exchange by convection between the external tissue and the environment. It was used a thermoregulation model to control the body temperature.

The model reproduced well the experimental data and can be used to predict thermal comfort conditions and local discomfort in subjects inside an acclimated environment.

simulation, occupancy effects, thermal comfort, numerical modelling

#NO 12200 Tools for evaluation of domestic ventilation systems.

Mansson L-G

UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 1, pp 322-327.

Within an International Energy Agency (IEA) project (Annex 27) experts from 8 countries (Canada, France, Italy, Japan, The Netherlands, Sweden, UK and USA) have developed tools for evaluating domestic ventilation systems during the heating season. Building and user aspects, thermal comfort, noise, energy, life cycle cost, reliability, and indoor air quality (IAQ) tools were developed. The IAQ tool accounts for constant emission sources. C)2, cooking products, tobacco smoke, condensation risks, humidity levels (i.e. for judging the risk for mould and house dust mites), and pressure difference for identifying the risk for radon or land fill spillage to enter the dwelling or problems with combustion appliances indoors. An elaborated set of design parameters were worked out, that resulted in about 17,000 combinations. By using multi variant analysis it was possible to reduce to 174 combinations for IAQ. A sensitivity analysis was made for 990 combinations. The results from all the runs were used to develop a simplified tool and a set of equations. The results can be used both for dwellings to be constructed and existing dwellings. The tools five immediate answers and indications, when discussing with the client about the consequences of different choices. Within this project also a computerised energy tool has been developed taking into account air tightness, climate, window airing pattern, outdoor air flow rate, heat exchange efficiency. This paper presents an introduction of the tools and demonstrate their applications.

ventilation system, residential building, tools, air infiltration, air tightness, natural ventilation, outdoor air, thermal comfort

#NO 12311 Microbial investigations and allergen measurements in ground-coupled earth-to-air heat exchangers.

Flueckiger B, Monn C

UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 5, pp 13-18.

Different ground-coupled earth-to -air heat exchangers have been constructed in many residential and occupational buildings in Switzerland to precool or preheat the incoming air. Many technical and energetic facts favour such systems. The objective of this study was to determine if microbial growth occurs within these tubes and if adverse health effects must be considered. The results show large reductions in viable bacteria and spore concentrations along the tubes and very low concentrations in the supply air compared to the outdoor air. Fungal allergens however, could still be detected in the supply air even if no or only very small amounts of spores were determined with the viable sampling techniques. Based on the results from this study the operation of ground-coupled earth-to-air heat exchangers is acceptable. Regular controls and cleaning of the facilities should be undertaken. 

allergies, health

#NO 12321 Heat and moisture exchange in counterflow rotary air dehumidifier.

Anisimov S

UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 5, pp 63-68.

This present work has theoretically investigated coupled heat and mass exchange mechanisms in counterflow rotary dehumidifier with the mixed desiccant of LiCI and additives, used in air conditioning systems. Mathematical model has been derived, based on one-dimensional transfer model and Polyni potential theory (theory of water chemical potential) and solved, using digital computer. The profiles of temperature and absolute humidity distribution in the matrix have been obtained. Analysis shows, that the direction of mass transfer is opposite to positive water vapour partial pressure. The results are presented in the form of the "overall effectiveness" of the heat exchanger. Dimensionless operating factors, affecting the efficiency of the heat exchanger have been investigated. The received results offer scope for estimation of variation range of rotary dehumidifier optimum operating conditions and suitable climatic zones for this unit. 

moisture, dehumidification

#NO 12478 Erdreichwaermetauscher fuer Wohngebaeude. Soil heat exchangers for residential buildings.

Pottler K, Hang I, Beck A, Fricke J

Germany, HLH, Vol 50, No 10, 1999, pp 48-53, 9 figs, 14 refs, 6 figs, 14 refs.

Soil heat exchangers provide an attractive possibility for fresh air preheating for residential buildings.

low temperature heating

#NO 12545 Ventilation and stratification in naturally ventilated spaces driven by heated internal vertical surfaces.

Cooper P, Hunt G

Australia, CSIRO and the University of Sydney, and IEA Energy Conservation in Buildings and Community Systems (ECBCS) Annex 35, 1999, proceedings of Hybvent Forum '99, First International One-Day Forum on Natural and Hybrid Ventilation, held at the University of Sydney, Darlington, NSW, Australia, 28 September 1999, pp 145-154, 8 figs, refs.

This paper reports on research into the fundamental fluid mechanics mechanisms that lead to thermal stratification in a naturally ventilated room containing sources of heat, or cooling. This aspect of natural ventilation has an important influence on both air exchange rates and thermal comfort in a naturally ventilation space. Particular attention is paid to the situation where the major source of heat is a vertical surface, such as a wall heated by solar insolation, for example. A theoretical model is presented that allows prediction of the ventilation flow stratification in such a room for the first time. Numerical results from this model and some preliminary experimental validation tests are presented. An example of how this theoretical model might be used by a designer for design of a naturally ventilated space subject to major heat gains at vertical surfaces is discussed.

numerical modelling, thermal stratification

#NO 12576 Simplified tools for evaluating domestic ventilation systems.

Mansson L-G, Orme M

USA, ASHRAE Transactions, Annual Meeting 1999, Seattle, 1 fig, 6 tabs, refs.

Within an International Energy Agency (IEA) project, Annex 27, experts from 8 countries (Canada, France, Italy, Japan, The Netherlands, Sweden, UK, and USA) have developed simplified tools for evaluating domestic ventilation systems during the heating season. Tools for building and user aspects, thermal comfort, noise, energy, life cycle cost, reliability and indoor air quality (IAQ) have been devised. The results can be used both for dwellings at the design stage and after construction. The tools lead to immediate answers and indications about the consequences of different choices that may arise during discussion with clients. This paper presents an introduction to these tools. Examples applications of the indoor air quality and energy simplified tools are also provided. The IAQ tool accounts for constant emission sources, CO 2 , cooking products, tobacco smoke, condensation risks, humidity levels (i.e., for judging the risk for mould and house dust mites), and pressure difference (for identifying the risk for radon or land fill spillage entering the dwelling or problems with indoor combustion appliances). An elaborated set of design parameters were worked out that resulted in about 17000 combinations. By using multivariate analysis it was possible to reduce this to 174 combinations for IAQ. In addition, a sensitivity analysis was made using 990 combinations. The results from all the runs were used to develop a simplified tool, as well as quantifying equations relying on the design parameters. A computerized energy tool has also been developed within this project, which takes into account air tightness, climate, window airing pattern, outdoor air flow rate and heat exchange efficiency. 

ventilation system, residential building

#NO 12592 Low-energy house with photovoltaic power system.

CADDET

Netherlands, Centre for the Analysis and Dissemination of Demonstrated Energy Technologies (CADDET), Result 356, October 1999, 4 pp, 1 fig, 1 tab.

A low energy house built in Kikuyo-machi, Kumamoto, Japan, has been designed with a high level of thermal insulation and is very airtight. The design has reduced the thermal-loss coefficient by 60% compared to a house with standard insulation. A central HVAC system with a heat exchange ventilation unit provides a comfortable environment. A roof mounted photovoltaic (PV) system supplies all the power required for air conditioning and cooking during the daytime under a clear sky. This eliminates the need for gas or oil. The special design of the house saves about 44% of the net energy costs compared with an average house in that area.

active solar power, low energy house

#NO 12793 The best-insulated house in the world?

Dumont R

USA, Home Energy, May/June 2000, pp 41-45, 2 figs, 2 tabs.

Describes the author's own self-built and highly insulated and energy efficient home, in Saskatchewan, Canada, which has recently been described by one researcher as having the lowest heat loss coeficient per square metre of floor area of any house in the world. The house has been carefully designed to incorporate the best aspects of energy efficient technology available, without sacrificing comfort or incurring excessive costs, and is designed to withstand the worst of the Sasketchewan climate, where the average January temperature is -18 Deg. C, and annual heating degree days total 10,900 (base 65 Deg. F), compared to the 8,400 of the "cold" winter city of Minneapolis, USA. Of particular note is the 16 inch thickness of blown cellulose insulation in the exterior walls, along with the very careful attention paid to air tightness (blower door test results were 0.47 ACH at 50 Pa). A balanced mechanical ventilation system provides the ventilation air, using a double core plate VanEE energy efficient air-to-air heat exchanger with efficient fans.

insulation, residential building, superinsulation

#NO 12870 Experimental and numerical study of a duct/heat exchanger unit for building ventilation.

Manz H, Huber H

Energy and Buildings, No 32, 2000, pp 189-196, 14 figs, 1 tab, 12 refs.

A mechanical building ventilation unit is presented that unites two functions: fluid transport and heat recovery. Aluminium fins in the supply air duct and in the adjacent extract air duct increase the heat flow to fluid. This unit is intended to be used mainly for residential ventilation and was investigated by means of experiments and simulations. Airflow rates, temperatures, air humidities and pressure differences were measured on a prototype device in an experimental set-up. Additionally, using a computer program for two-dimensional heat conduction analysis and a simple analytical model, the efficiency of heat recovery was calculated and compared with measurements. Afterwards, the influence of variations of the heat exchanger geometry on thermal efficiency was investigated by means of simulation. It was sown that using this concept it is possible to realize a ventilation unit with high-efficiency heat exchange, e.g. temperature efficiency of 0.7 at a duct length of 6m. 

residential building, heat exchanger, duct

#NO 13031 Air to air energy recovery.

Besant R W, Simonson C J

USA, ASHRAE Journal, May 20000, pp 31-42, 6 figs, 11 refs.

Auxiliary energy loads for supply air heating or cooling sometimes can substantially reduce the need for dehumidifying or humidifying by using air to air heat or energy exchangers. The most important factors in reducing HVAC capital and operating costs are ventilation airflow requirements, climatic parameters, exchanger recovery system performance factors and duration of operation. This article provides guidance on the types of heat or energy recovery devices and how to select one, how such a device should be integrated into an HVAC system, what one can expect for performance factors, sizing, and likely payback period. Concludes that applying air to air heat/energy exchangers in buildings is a cost effective and reliable way of conditioning outside ventilation air. For many climates and applications an energy wheel is favoured, while sensible heat exchangers are favoured in others. The article shows that air to air heat/energy recovery can reduce significantly the capital costs and energy consumption of auxiliary heating and cooling equipment. For a retrofit, the payback on investment may be several years. In new applications the payback may be immediate because a carefully designed HVAC system, which includes energy recovery, will often have as low or lower initial costs as a system without energy recovery. In this case, the energy savings that accrue will result from essentially no investment. Air to air heat and moisture exchange for ventilation air is important for HVAC design and operation because it can: reduce peak auxiliary energy rates and annual loads as well as capital and operating costs; permit higher ventilation rates to create better IAQ at minimum auxiliary energy costs.

air to air heat recovery, indoor air quality, air flow rate

#NO 13090 A novel ventilation heat pump system.

Riffat S B, Gillott M C

UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 41.

The move towards improving building air-tightness to save energy has increased the incidence of poor indoor air quality and associated problems, such as condensation on windows, mould, rot and fungus on window frames. Mechanical ventilation heat recovery systems (MVHR) combined with heat pumps offer a means of significantly improving indoor air quality as well as providing heating and cooling required in buildings.

This paper is concerned with the testing and performance of a novel ventilation heat pump system developed for the domestic market. The novel system uses revolving heat exchangers with both impel air and transfer heat. Low grade heat recovered from the exhaust air is upgraded by a heat pump and used for heating the fresh supply air. The prototype system has a heating coefficient performance (COP) of up to 5 and an average system COP of 2.5 over a range of conditions. The system typically provides 2kW of heating for air supplied at 250m3/hr. The system can also be used for cooling by switching the air flows over the evaporator and condenser. The prototype system requires very little maintenance and is compact and energy efficient.

heat pump ventilation, mechanical ventilation, indoor air quality

#NO 13092 Energy efficiency of ventilation systems.

Maas A

UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 43.

The paper presents a short description of the measurement program and the data collected for the "SynergieHaus"-project initiated by PreussenElektra and partners (now merged to E.ON). Results of airtightness measurements (ACH 50-values) are shown for a total of 320 buildings equipped with ventilation systems. It was found that both for massive (brick) and light (wood frame) buildings a high standard of airtightness can be obtained.

Based on calculations of heat use according to valid German heat conservation regulations "W„rmeschutzverordnung", a comparison between measured heat consumption and calculated heat use is presented. The comparison leads to effective air change rates for different ventilation systems which depend on the flow rates and the efficiency of the heat exchanger.

The energy efficiency of the technical equipment can be expressed by the ratio of measured total energy consumption for space heating, preparation of hot water and ventilation and the calculated heat use. Average values for different ventilation systems are presented.

The different functions and ways of control of ventilation systems lead to different electric power consumption of the fans. For each of the various ventilation systems an average specific power consumption is shown.

energy efficiency, ventilation system, air tightness, air change rate, heat exchanger


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