Numbers of Abstract/Session (given by NOC)

-1-A DEVELOPMENT OF A HEAT PUMP FOR A THERMAL RECOVERYSYSTEM USING CO2 AS A REFRIGERANT
Hiroshi Soma
Senior engineer, engineering development department, Chemical grouting Co., Ltd.
2-2-5 Toranomon, Minato-ku, Tokyo 105-0001, Japan
Kenji Iwasawa
Company president of MDI Corporation
1-4-13-503 Kaizuka, Kawasaki-ku, Kawasaki-city, Kanagawa 210-0014 Japan
Kenji Fukumiya
Company president of Agri Cluster Corporation
2-3-2 Kamiochiai, Chuo-ku, Saitama 338-0001 Japan

Abstract: This paper discusses the capacities of CO2 as a refrigerant that recovers
geothermal heat and waste heat from storage tanks. The CO2 allows heat exchange throughlatent heat. Thus, it increases the exchanger duty per unit length of a heat collection pipe,
which drastically reduces the heat pump installation cost and running cost. In this study,
authors created pilot versions of an air conditioning system using geothermal heat and a coldand hot water production system using waste heat from a storage tank with CO2. Authors
evaluated their performance and electricity consumption. As a result, the air conditioning
system showed about the same air conditioning abilities as a system with propylene glycol,
which was installed for comparison when the installed length of the heat recovery pipe was
one-third to one-half, and the electricity consumption was one-half with the CO2. Meanwhile,the cold and hot water production system that used waste heat from a storage tankrecovered as much as one to nine kilowatts of heat capacity per meter of a heat collection
pipe when the CO2 was used.
Key Words: Heat Pumps, Geothermal Recovery, CO2, Latent Heat, Cost Reduction
1INTRODUCTION

The heat pump technology has been attracting attention in recent years for its lower runningcost and CO2 emissions in comparison to systems that use fossil fuels. The demand for heatpumps for air conditioning, both heating and cooling, has been increasing in the field ofprotected horticulture because the inside of greenhouses needs to be kept at a constanttemperature throughout the year depending on the crops produced. However, common heatpump systems use the air as a heat source; thus, they need to work under extremely large
loads when they recover and release heat in cold regions where the temperature drops
below zero and in extremely hot summer, like the summer in Japan in 2010, when thetemperature rose above 40 °C. Thus, the load on the systems can be reduced if the heat isrecovered underground where the temperature is relatively constant. In addition, the systemreleases the heat underground rather than into the air during cooling, which becomes aneffective way of mitigating the heat island phenomenon. To recover geothermal heat, thesystem now exchanges heat through sensible heat by circulating the water refrigerant towhich anti-freezing agent was added through pipe laid underground. Yet, the high initial costfor laying the pipe has been considered as one of the obstacles in promoting the system.
When a system uses CO2 refrigerant to recover geothermal heat, it means latent heatexchange, which increases the exchanger duty per unit space of laid pipes. This decreases

10thIEA Heat Pump Conference 2011, 16 - 19 May 2011, Tokyo, Japan