The LTHP wouldn't work if it weren't for an impressive array of sensors and controllers that place the different components in the system into action in the proper sequence at the proper time. Energy is never used to supply excess capacity to the system. The indoor thermostat is a two-step model, which alters the capacity of the system based on small variations in indoor air temperature. When the thermostat first calls for heat, only 50 percent of the primary compressor's capacity is energized until the outdoor ambient air temperature drops to 40 degrees Fahrenheit, when the primary compressor begins working at 100 percent of capacity. The booster compressor won't come on until 25 degrees, and only if the second step of the thermostat calls for it. At 5 degrees, the subcooling economizer is activated, but again, only if the second step of the thermostat calls for it.

How well LTHPs perform

The graphs on page 166 show the actual performance of the LTHP units that are now under development at Hallowell International, according to measurements taken in the company's labs. Shaw says they have been verified by an independent lab, as well. Above 30 degrees Fahrenheit, the energy efficiency of the LTPHs is fairly consistent with most common heat pumps, but as Shaw says, "Below 30 is where the action is." One of the graphs shows the performance of a 3-ton LTHP, in Btu per hour, compared to a conventional heat pump, as the exterior temperature falls. At 0 degrees, with the economizer, primary, and booster compressors all running, the LTHP is keeping up with the heating load, but the air-source heat pump cannot keep up below 25 degrees. The other graph shows coefficients of performance (COP) for the two heat-pump types. The COP is the ratio of the energy transferred for heating to the input electric energy used in the process-the higher the COP, the more efficiently the unit operates. Below 30 degrees, the efficiency of the heat pump using resistance heating drops very quickly. At 0 degrees, the typical air-source heat pump has basically stopped producing any heat and is using only its electrical-resistance heat, which has a COP of 1, while the COP for the LTHP is 2.23.

So, can the LTHP change the world? Not just yet. E Source's studies show that the calculation of an owner's payback for installing one, as compared to a furnace, differs greatly by region and involves such variables as prevailing costs for fossil fuels, electric rates, and weather conditions. Often, both furnaces and water heaters have to be changed to electric models in order to make the numbers work, so utility companies will have to embrace the technology and push it to their customers aggressively.

For any innovation in the HVAC industry to succeed, sales, distribution, and installation training obstacles have to be overcome, not to mention the kind of manufacturing problems that plagued the first generation of LTHPS that made it into the field. Probably, the hardest thing to overcome is cultural: It's simply the reluctance of both utility companies and consumers to place their trust in a new product, even if the technologies that made it possible aren't new. Hopefully, the optimism that inspired David Shaw to come this far will continue to encourage him and his company to keep trying.