Exhaust Air Heat Pump Research Articles

Energy analyses of buildings equipped with exhaust air heat pumps (EAHP)

The article deals with the theme of thermal recovery from exhaust air through heat pumps (EAHP). After a description of the main features of this technology and a classification of the possible systems, the technical characteristics and performances of an EAHP, which have been validated through field and laboratory experimentation, are illustrated. The heating and cooling energy performances of buildings equipped with this kind of thermal machine have been validated, addressing themes such as the dimensioning of the EAHP, the fraction of the requirements of maximum power or of useful thermal or cooling energy covered by it, the mean seasonal yield and the primary energy requirements. The energy analyses, carried out on an elevated number of test cases in order to be able to draw as general considerations as possible, have been elaborated through an evaluation model of the dynamic thermal behaviour of the building-plant system, implemented in a Matlab Simulink® environment, and validated through a comparison with the most well known simulation programmes.

Modelling and simulation results for a domestic exhaust-air heat pump heating system

Energy consumption in residential buildings has gained an increasing interest the latest years due to the rising demand for efficient energy use and higher comfort standards. In tight building constructions with controlled ventilation, heat recovery with exhaust-air heat pump connected to floor heating is regarded as energy efficient heating system that optimises the energy use in buildings while maintaining an acceptable level of thermal comfort. In this study, we use the computational tools TRNSYS and EES to model and analyse the performance of a residential house, its ventilation system and its floor heating system based on an exhaust air heat pump. The system analysis focuses particularly on the influence of internal and solar gains on the operation of the heating system and the thermal comfort of the house. Furthermore, the way that gains influences the performance of the floor heating system is examined. Overall, the results bring to light the impact of factors that are not easy to predict on the indoor climate and the thermal comfort.

Exhaust air heat recovery in buildings

The technique of heat recovery from ventilation air in dwellings started in Sweden in late 1979. This was due to an energy crisis and new building codes. The competing heat recovery system, air to air heat exchangers, had a firm grip on the market. Today the situation is on the contrary. Almost all new single family houses are equipped with exhaust air heat pumps. This paper describes the development of the market in Sweden and Germany and also the different techniques of supplementary heating due to national differences in electricity prices. Germany has a situation very similar to Sweden concerning new building codes concerning the allowable energy use for space heating. Starting in 1976 and continued from 1982 to 1995, the building code has prescribed tighter and more insulated houses. The new building code for the year 2000 contains requirements for well insulated and tight buildings so the energy demand for heating from ventilation air tends to reach about 60% of the total annual energy demand for the building. Under these circumstances new buildings must have ventilation systems with heat recovery. Different means of heat recovery from the ventilation system, and the benefit for the environment, by using heat pumps are described. The German market for heat recovery systems is approx. 5–10.000 units/year. Most important for the efficiency of a ventilation system is to maintain the quality criterias concerning: equipment planning, installation, taking into operation operation.VEW ENERGIE AG has accomplished a field survey of 60 units from 1994 to 1996. As the result was not statistically sufficient, the field survey is followed by an investigation into air quality and reliability.

Low energy consumption in Swedish single-family houses

In Sweden, as well as in many other countries, the energy consumption in residential buildings is a burning question. Due to this, the thermal insulation and the tightness of new buildings gradually has been increased. A well defined ventilation is because of this even more important, and the minimum level is given in regulations prescribed by the National Board of Housing, Building and Planning. To fulfil the regulations it is almost necessary to use mechanical ventilation. Since an ordinary ventilation causes a substantial energy loss it is of vital interest to reduce this. The most efficient way of reducing the ventilation loss, is to use an exhaust air heat pump which recovers energy from the exhaust air and supplies it to heating and hot water. In Sweden there have been about 100.000 units installed in single family houses until today. The paper will describe the regulations, the ventilation system, the exhaust air heat pump and the results achieved when installed in single family houses.

Is space heating in offices really necessary?

New office buildings in Sweden are thoroughly insulated due to the Swedish building code. This code, however, does not consider the type of activity occurring in the building. This means that the heating equipment is designed as if no activity at all is going on. In modern offices there is a lot of equipment installed which uses electricity. This electricity is converted into heat which can be utilized for heating the premises, mostly in a direct way but also by the use of exhaust-air heat-pumps or heat exchangers. This paper deals with a modern office building plus office hotel complex located in Linköping, Sweden, about 200 km south of Stockholm. The tenants deal with the design of hard- and software for computers. The lighting and computers in the building use electricity which converts into heat. In this paper, it is shown that this electricity is all that is needed during normal conditions, i.e. when people work in the building. The building is also equipped with a district-heating system, which is designed as if no activity goes on in the building, so subsequently the heating equipment is larger than it need be. In this special case, it might have been better to install an electric heating device for hot-water heating and very cold winter conditions, instead of using district heating. This is so even if district heat is about half the unit price compared with that due to the dissipation of electricity. At present, when district heating is used, no measures for saving heat can be profitable due to the low district-heating price. The fact is that the tenants complain of too much heat instead of too little: the prevailing indoor temperature was about 24° C in January 1990 even though 20° C would have been sufficient. There is subsequently a need for a properly working regulation system. The one currently in use is designed to a modern standard, but is not able to maintain temperatures at a modest level.

Exhaust-air heat-pump performance with unsteady-state operation

The energy performance of two residential exhaust-air heat pumps (EAHP) with different condenser designs was studied experimentally in a laboratory with a focus on transient heat-pump performance associated with time varying requirements for water and space heating. Experimental variables included the total daily volume of hot water required, the schedule of hot-water demand, the temperature of water entering the hot-water tank, hot-water delivery temperature, and the temperature and flow rate of air entering the auxiliary refrigerant-heated fan coil supplied with one of the EAHP units to permit space heating. Based on the data, for a wide range of operating conditions, we derived linear correlations between the heat-pumps' time-average coefficient of performance (COP) and appropriate spatial and temporal average temperatures in the hot-water tanks. With the refrigerant-heated fan coil, the COP varied non-linearly with air flow rate. COPs ranged from 2.0 to 4.2. The control system of the EAHP with two condensers (one is the fan coil) gives priority to water heating. Based on the data, results from our previous hourly modeling of EAHP performance, data from field studies in Sweden, and new calculations, we propose a new control system that usually places priority on space heating and, thus, takes better advantage of the capacity to store heat in the water tank. We estimate that this proposed control system may increase annual energy recovery by approximately 1000 kWh if the EAHP is used in a Portland, Oregon house. Total annual energy savings due to EAHP operation in an all-electric house (compared to the same house with electric resistance space and water heating) is estimated to be approximately 6000–7000 kWh.

Assessment of residential exhaust-air heat pump applications in the United States

We provide a technical and economic assessment of residential exhaust-air heat pumps for water heating with an option for space heating. Compact one-cabinet heat pump units containing a hot water tank with refrigeration condenser, exhaust fan, refrigerant evaporator, compressor, and controls have recently become available on the U.S. market. The emphasis is on U.S. applications with three representative climates: moderate (Northwest), cold (Midwest), and hot and humid (Southeast). Our approach is to simulate detailed system performance for a full year for two typical houses equipped with the heat pump. Ventilation and energy performance of the heat pump houses is compared to the same houses equipped with air-to-air heat exchangers and to naturally ventilated houses. Exhaust-air heat pumps are found to provide a nearly constant ventilation rate throughout the year, as opposed to the natural ventilation rate that is found to be highly variable. Energy savings realized with the heat pumps are greater than those obtained with heat exchangers. Both heat pumps and heat exchangers are cost-competitive with natural ventilation in cold climates and are clearly uneconomical in hot and burned climates with present electric rate predictions.