Energy roof as heat pump source/sink R. M. Lazzarin and L. Schibuola Istituto di Fisica Tecnica-Universita' di Padova, via Marzolo, 9-35100 Padova, Italy Received 23 October 1985 An energy roof was considered both as a source for a heat pump and as a sink during the summer for a machine acting as an air conditioner. Performance looks very promising compared with similar systems which are equipped with finned coils utilizing the outside air as source/sink. (Keywords:heat pumps;energy roof) Toit 6nergbtique comme source et puits thermiques d'une pompe chaleur On a considers; un toit dnergdtique d la fois comme source et puits thermiques d'une pompe d chaleur fimct ionnunt en ~;t~; en conditionneur d'air. La performance paraft prometteuse en comparaison arec des syst~mes semblables munis d'~chanoeurs d ailettes utilisant Fair ext~rieur comme source et pulis thermiques. I Mots cl/~s: pompe fi chaleur: toit energ&ique) An energy roof is a roofing system for buildings which allows simultaneous collection of energy directly from the sun and from the air, by means of a fluid which flows in channels in thermal contact with metallic tiles. When used as a source for a heat pump large collecting areas can be obtained with a low installation cost. However, they are not glazed, so higher losses are to be expected than in solar collectors. This application has been studied for some time' ,o. In summer the energy roof can be utilized as a sink for condenser heat from cooling equipment. This application has been considered only recently ~ a. The annual behaviour of such a plant will be discussed. The plant is sketched in Fiqure ! in the winter mode and in Fiqure 2 in the summer mode. During the winter a heat pump supplies the heating via a storage tank. The highest temperature in the tank is set at 46 :C and the lowest one for heat pump starting is at 4OC. However, the heat pump only works if the energy roof is able to provide thermal energy at temperatures > -2 'C. The same tank is utilized in summer in connection with the roofwhich provides a sink for thermal energy, whereas the heat pump works as a chiller. The incorporation of a storage system is important; in fact, the chiller works mainly during the day, whilst cooling through the roof occurs effectively during the night. System performances have been studied by means of a modified version of transient system simulation (TRNSYS) on the data collected at 10 min intervals by the meteorological station of the Institute for Refrigeration, CNR, Padova, Italy. The most important modifications of TRNSYS were those describing the energy roof and the heat pump/chiller. The energy roof considered ]s made by IOM 5rl I Musile di Piave, near Venice, Italy) with rhombic copper tiles (Fk,/ure 3). The roof can be either closed or ventilated. In the former case, an air layer is delimited by the roof slope and the cover with insulating effects. In the latter 0140 7(.R)7 ~6 {)21110~ 05$03.00 1986 Buttcr~orth & ('o (Pubhshcrs) Lid and IIR 108 Int. ,J. Refrig. 1986 Vol 9 March case, the air layer is communicating with the outside at the bottom and top of the roof: air movement is thus favoured and this increases the useful heat exchange whenever the roof temperature is below (above in summer) the outside air temperature. To compute the convective exchanges, the model proposed by Sparrow was used 12'13. The results seem more reliable than those obtained by McAdams ~4. The heat pump was described by means of performance curves of a commercially available machine of the water- water type. These curves are presented in Figure 4. This machine works with a maximum input temperature to the evaporator of 22'C. Above this there are harmful overpressures; therefore, in Figure 1 the valve V I was set to control the input temperature to the evaporator. Fi,qure 5 illustrates the performance of the chiller for summer working. The simulation relates to a single family home with a volume of 747m 3 and an area of 207.5m'. Insulation is as prescribed by Italian standards. The roof has four sloping sections, each one orientated toward a cardinal point. The north and south slopes have equal areas of 81 m 2 with a slope of 15.5. The computations of the summer and winter loads are obtained with thc transfer function method (ASHRAE). Performances in the heating mode Before analysing plant behaviour, a preliminary study was carried out, so that some operational parameters could be correctly chosen; among them the storage capacity and the specific flow rate. The increase in performances, both in terms of the load fraction. F, covered by the heat pump and of COP. demonstrated that there was little advantage in a storage size of >3 m3: therefore this value was used. A good specific flow rateis ~20kgh 'm 2. The behaviour of the closed roof was compared with the ventilated system. Better results were obtained for the