In 1983, when oil process were till high in my area, I installed a ground-source heat pump in my brand-new, and insulated 1,600-square-foot house. It cost several thousand dollars more than comparable systems that use oil, gas, or wood, but I figured I’d recover my higher initial expense in a few years through lower energy bills. True, my heat pump runs on electricity-an expensive commodity where I live. But most of its energy comes from the earth: a propylene-glycol solution circulates through 1,200 feet of two-inch-diameter plastic pipe buried three feet deep in a field next to my house. As it travels, the solution absorbs heat from the surrounding soil, even when soil temperature drops below freezing. My ground-source heat pump also offers important benefits that have nothing to do with economics. *Minimal fire hazard-no chimney, firebox, or heating elements-only pumps, fans, and a compressor. *Cleanliness-no combustion products, thus no chance of my heating system polluting the indoor air, leaving scummy deposits on walls and furniture. *Reliability-solid-state electronic controls and sealed bearings almost eliminate breakdowns. *No maintenance-no wood’ to cut, ashes to haul, or chimney to clean. *Convenience-the system runs automatically, even switching from heating to air conditioning as needed. I can simply lock the door and go away for a day, week, or month. Not only did I expect to start saving on energy costs immediately, but I also expected those savings to grow over the years as oil process continued to soar. Since I was wrong about oil prices, the big dollar savings I’d hoped for haven’t materialized. Nevertheless, I am satisfied, all things considered.
A．soil in a nearby fieldB．sun panels at ground levelC．a pipe buried next to the wallsD．a tank of propylene glycol
点击查看答案
题目内容
（请给出正确答案）
参考答案
十点题库官方参考答案
（由十点题库聘请的专业题库老师提供的解答）
