By George Harvey
It might come as a surprise to some of us, but nearly everyone has and uses heat pumps. They drive our refrigerators, air conditioners, and even dehumidifiers. In the past few years, new technology has made them economical for heating homes in the northeast. But one thing even more of us do not focus on is that the same technology that heats homes during the winter, can keep us cool the summer, and do it more efficiently than dedicated air conditioners.
We connected with Kim Sager of ARC Mechanical Contractors, from Bradford, Vermont, for information on details. She told us that heat pumps beat out other forms of both heating and cooling in almost all ways. Specifically, she said, “Heat pumps compare very favorably to other types of heating and cooling systems in terms of installed cost.”
She also addressed the carbon impacts of heat pumps, saying, “As far as environmental impact, it all depends. Heat pumps use electricity to operate, so it all depends upon how efficiently the electricity was produced.” If we have solar systems or other renewable energy driving them, operating them can be carbon-neutral.
Heat pumps can be air-sourced (ASHP), also called mini-splits, water-source, or geothermal, so we asked Sager about the different kinds of heat pumps and whether they can all be used for cooling. Her reply was, “All heat pumps heat and cool regardless of the source, air or water.”
She directed us to a quote from a US Department of Energy website for a comparison of different kinds for efficiency: “…geothermal heat pumps are substantially more energy-efficient than even air source heat pumps because they take advantage of the relatively consistent ground temperatures, which are far more uniform than air temperatures. Geothermal systems can reduce energy consumption by approximately 25% to 50% compared to air source heat pump systems. Geothermal heat pumps reach high efficiencies (300%-600%) on the coldest of winter nights.” [bit.ly/DOE-geothermal-HP-guide]
There are different kinds of ASHPs, and we asked about permanently installed ones, as opposed to those that can be mounted in a window, like an air conditioner. To this, she said, “SEER and EER ratings will tell you how efficiently a unit performs, the higher the rating the less expensive it will be to run the unit. A quick online Home Depot search found three window heat pumps: a 9,000 BTU unit for $615; an 11,600 BTU unit for $700; and a 17,300 BTU unit for $867. All units advertised up to a 9.8 EER rating. Compared to a 9,000 BTU ductless-split cold-climate heat pump system installed for $3,850 with an EER of 16.1, a window unit is certainly less expensive albeit much less efficient.”
Specifically, she said of her own experience with makes and models, “For residential and small commercial applications, we install more Mitsubishi Electric heat pump systems than any other. We also install quite a few Fujitsu systems. Both manufacturers produce reliable, robust cold-climate heat pump systems.”
One interesting thing about heat pumps is that they can be used for some other pretty specific jobs. For example, there are special units that are designed to take heat from a basement environment and deliver it to a water heater. As a side benefit, their cooling can be used to condense water vapor and deliver it to a drain or sump. This means a heat pump can do double duty, dehumidifying the cellar while it heats water. Sager observed, “A dedicated de-humidifier operates off a humidistat that is sensing the humidity level of the space. The heat pump water heater reacts to the temperature of the water in the tank and will only dehumidify when there is a demand for hot water, and the compressor is running, regardless of the space humidity.” Nevertheless, the heat pump is not only a highly efficient way to heat water, but the energy that is lost in the process can be used for the purpose of dehumidifying, a clear gain.
The bottom line for summer heat, however, is that while mini-split or geothermal heat pumps are among the most efficient and environmentally-friendly ways to heat buildings, they are also quite possibly the most efficient and environmentally-friendly way to cool them.
Meriden Library Installation
ARC installed a Mitsubishi Electric ductless heat pump system at the Meriden Library, in Meriden, New Hampshire. Not only will the library patrons stay cool when summer heats up, but the new system will also provide heat when winter returns, reducing their reliance on their oil-fired furnace.
The Meriden Library Director, Mary King, is excited to be able to offer patrons a comfortable refuge in the heat of the summer as well as realize savings from the efficiency of the heat pump.
The multi-zone, Mitsubishi Electric, 36,000 BTU, heat pump system that was installed includes an outdoor condenser with two indoor evaporators. Even when the outdoor temperature falls to 17 degrees, the system will provide heat at 75% of its capacity, reducing the library’s heating oil expense.
The Meriden Library, like many small town libraries, had limited funds, and although air conditioning was needed, it seemed like a luxury.