【正文】 ntrolled forced ventilation for maximum energy saving and fort. There is a large variation in the fresh air requirement for people depending on the situations. ANSI/ASHRAE Standard 622001 remends 30–54 m3/(h person) of outdoor air for mercial buildings[3]. In a central air conditioning system, the necessary amount of outdoor fresh air is calculated based on the upper limits of the concentrations of air pollutants of indoor air and often has the value of 10–30% of volumetric air ?owrate of recirculation air [4–6].Ventilation, though essential for maintaining acceptable indoor air quality, is always acpanied by energy loss since outdoor air must be cooled or heated to bring it to the pace condition. Fig. 1 shows percentage of heating load increase due to outdoor ventilation for a standard heating operation condition. In the ?gure, it is shown that for an outdoor ventilation of 30%, heating load has been increased by % pared to none outdoor ventilation. For the calculation, it has been assumed 21 8C, 45% for indoor,7 8C, 6 8Cwbfor outdoor condition, and 8C for supply air temperature. In Europe, the 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 [7]. Since a large amount of energy is lost due to ventilation, it is very important to recover ventilation energy.Though important, relatively few works related to recovering ventilation energy can be found in the work of Besant et al. [7,8] on airtoair energy recovery is a survey of the air ?ow con?guration, devices and performance factors for a ventilation heat recovery of selecting a heat or energy recovery device based on temperature and humidity differences was , some economic aspects related to the payback duration of an energy recovery system were considered. The authors of this work concluded that applying airtoair heat/energy exchangers in buildings is a costeffective and reliable way of conditioning outside ventilation air. Fehrmet al. [9] described the development of the ventilation systems with heat recovery in Europe. From a ?eld survey of 60 units, forced ventilation systems featuring heat recovery equipment reduced ?nal energy consumption by 20%. Dieckmann et al.[10] claimed that in a reasonably tight building, energy recovery ventilators can reduce annual cooling and heating energy consumption by about onethird.The objective of this work is to study the overall performance of heating mode heat pump for various heat recovery systems during forced ventilation. A heat pumpbined with a ventilation system is built for this research and tested in two constanttemperature and constanthumidity chambers. Methods for recovering sensible heat tested in this work are by a separate sensible heat exchanger, introduction of indoor air to the evaporator to increase the evaporator pressure, and ?nally a bination of forementioned two coef?cient of performance (COP), refrigerant based COP, refrigerant mass ?ow rate, air based heating capacity, refrigerant based heating capacity, highside pressure, lowside pressure, pressor work, supply air temperature, evaporator exhaust air temperature are measured and pared with the case of none ventilation heat recovery.2. Methods for recovering heat during ventilationSeveral types of airtoair exchanger recovery devices are available for recovering energy from ventilation. The heat exchanger may transfer sensible heat only or bothsensible and latent heat. Over many decades, plate type,regenerative wheels, and heat pipe exchangers were developed and used to transfer heat for a variety of airtoair applications. Typical heat and enthalpy exchange ef?ciencies range from 55 to 80% [11].3. Description of the test apparatusTo test the performance of three types of heat recovery systems for ventilation and pare with none heat recovery case, a heat pump system and two thermal chambers were built. Two thermal chambers were used to simulate the indoor and outdoor temperature and humidity conditions for heating mode. 4. Analysis of the experimental resultsFor the experiment, temperature and humidity of the two thermal chamberswere controlled to satisfy the standard heating condition of 21 8C temperature, 50% relative humidity of indoor and 7 8C temperature, % relative humidity of outdoor. The system state is considered steady if all data values stay within acceptable tolerances in a period of at least 5 min. The allowed errors for both dry and dewpoint temperature are 8C. To verify the repeatability,each experiment case was tested repeatedly 3 times with a recording time of 5 min each. Total of nine experiment cases were performed. Five ventilation ?ow rates (0, 75, 150, 225, 300 m3/h) were tested with type C whereas four ?ow rates were done with type D. All of these experiments were done with the air ?ow rate of 1300 m3/h for indoor supply and 3150 m3/h for outdoor exhaust. The percentage standard deviation of all the data values is %.Though the performance characteristics of sensible heat exchanger were provided by the manufacturer, they were measured in this work since discrepancy may occur between the actual performance and the given data. Ventilation ?ow rates were varied from 75 to 300 m3/h, a range that has been used for the ventilation in this work. 5. ConclusionsIn this work, three methods of recovering sensible heat during ventilation and heating process of heat pump have been studied experimentally. Those heat recovering methods are by a separate sensible heat exchanger,introduction of indoor air to the evaporator (single heat recovery), and a bination of the forementioned two methods (double heat recovery). An airsource heat pump system that can recover ventilation heat by three methods has been built and tested in two constanttemperature and constanthumidity thermal chambers that simulate the standa