Economics of Greenhouse Heating with a Mine Air-assisted Heat Pump

Abstract

ABSTRACT. An G reenhouses require significant energy inputs to maintain an optimum environment for crop production. In fact, for a commercial greenhouse operation, energy costs typically account for 15 to 40% of plant production costs (Aldrich and Bartok, 1989). The source of this energy is generally driven by economics; coal, fuel oil, and natural gas are commonly employed. The relatively high cost of electricity has historically precluded its use as a fuel for greenhouse space conditioning.An electric air-to-air heat pump uses a working fluid or refrigerant to absorb heat from one location and carry it to another. The cost per unit of useful heat delivered is much less for a heat pump than for electrical resistance heat. Unfortunately, as the outside air temperature decreases, the amount of heat that can be extracted from the outside air and transferred into the conditioned space also decreases. Also, as the outside air temperature decreases, the heat required to maintain the desired temperature in the heated space increases. During relatively mild periods, a heat pump can deliver three to four times more heat energy (by extracting heat from the outside air) than it uses in electric energy. However, during periods of extreme cold, both the efficiency of an air-to-air heat pump and its output capacity decline dramatically. Figure 1 presents curve for an air-to-air heat pump based on product performance data from Carrier Corporation (1989).Many strategies have been attempted to avoid decreases in both output capacity and operating efficiency of heat pumps that occur due to decreasing ambient temperatures. Two examples of these strategies include: 1) solar-assisted heat pumps that couple the evaporator side of the heat pump witii a passive solar collector (Smith, 1984), and 2) earth-coupled or ground-source heat pumps that couple the heat pump to a buried pipe, which acts as a heat exchanger (Bose et al., 1985).This article addresses the feasibility of coupling the evaporator side of a heat pump with an inactive mine shaft. The U.S. Bureau of Mines reports the existence of over 88,000 inactive or abandoned mines in the United States 80 3

Theoretical Analysis and Experimental Research on the Braced Stress of Vacuum Glazing

“…In Fig. 3, a pillar radius is r, because r<0.5t, then proceeds calculation by equivalent contact radius r′replaced r, its calculation method is shown as follows [3,4]:…”

Automated Control System for Alternative Energy Supply of a Mining Enterprise

“…One promising direction of heat pumps application is the using of low-temperature renewable energy sources of mines [10,11].The use of mine water for space heating or cooling purposes has been demonstrated to be feasible and economic in applications in Scotland, Canada, Norway and the USA [12].…”