This winter’s must have accessory

With fuel prices through the roof, this winter’s must have accessory for fuel heated homes besides a sweater, is a window heat pump unit. Yes, heat pumps only work well when the temperature is above 20 F, but when conditions are right they are far more efficient than fuel fired heating, since they move heat with energy not make it. This means that for part of “heating year” even a kluge like a window heat pump, if it has a super insulated window insert and excellent seals can take a significant load off the furnace. I did some calculations with numbers I got off the web and throughout most of the Northeast with window heat pumps supplementing gas or oil furnaces people could shave >$100 a month off their heating costs. (If they installed a dual fuel system and we discount the cost of heating water the savings would be >$200, assuming electricity if $.1/KWH and heating oil is $4.50 a gallon.)

What would be most interesting would be the addition of solar thermal panels to supplement the efficiency of air sourced heat pumps. (Solar thermal panels are sheets of glass and anodized aluminum separated by a vacuum so the incident light heats the metal and the working fluid behind it, so they are cheaper than photovoltaic cells.) Like AC units that make ice during the night, during the day the solar thermal panels would heat up and transfer the heat to a thermal mass or phase change media. The coils would then absorb heat from the media and heat the house. Even in the dead of winter if it is sunny a south facing solar thermal panel can heat up to over a hundred degrees. This system could give low cost air sourced heat pumps SEER ratings approaching 3.5. In times of excess capacity or when the AC is on, the system could be used to preheat domestic hot water. Water comes out of the pipes at ~55 F so warming it to 115 F requires its temperature to rise 6o degrees. So raising the temperature of a 40 gallon tank to usable levels requires almost 20,000 BTUs, or a tenth of a gallon of heating oil, a tenth of a Therm of natural gas, or almost 6 KWH of electric. If you can increase the temperature of the water to 75 or 80, you can almost halve the number of BTUs needs, the savings add up quickly.