GLASTONBURY, Conn. - A new 9,000-square-foot Colonial-style house is now being heated and cooled by two natural gas-fired absorption heat pumps. This is the first residential installation of these unique heat pumps, which have a rated efficiency of 126 percent. That means for every dollar the homeowners spend to operate these heat pumps in heating mode, they will receive an average of $1.26 in energy returned.
This one-of-a-kind, energy-efficient, multi-million-dollar home was completed in April 2007. Its $125,000 HVAC system includes the absorption heat pumps, which serve a radiant heating and hydro-air heating and cooling system, as well as high-efficiency air cleaners, humidification, programmable thermostats, and zoning. The ductwork, which was installed in the conditioned space, was wrapped and its joints sealed to prevent leakage.
Mark Falade, president, Marx Diversified Interests, Hebron, Conn., designed and installed the heating and cooling systems in conjunction with Progressive Sheeetmetal, Manchester, Conn. Falade said it was very rewarding to work with such forward-thinking homeowners. “They wanted high-efficiency equipment that would give them the most bang for their buck, and we were able to provide that.”
NOT THE ORIGINAL DESIGNThe Glastonbury home was not originally designed to be conditioned by the absorption heat pumps; instead, the plan called for using six air handlers with conventional air conditioning and several high-efficiency boilers. The homeowners threw Falade a curve ball, though, when they asked him to look at other high-efficiency options.
Falade had previously worked with Servel (now Robur) equipment, and he knew the company offered a high-efficiency combination boiler-chiller system that could potentially work in this application. “I went to look for the original product, and there was the new heat pump. The numbers were amazing as far as I was concerned. I couldn’t believe that anything out there would do something like this. It’s the first product that takes an ammonia absorption chiller and reverses that process and uses it to produce heat.”
Indeed, the Robur GAHP-AR air-source to water-ammonia absorption heat pump uses natural gas as the primary energy source to supply hot water up to 140°F or chilled water down to 37.4°. The same unit is suitable for heating or cooling by reversing the absorption cycle, using the outside air for heat rejection in cooling mode and as a heat source in heating mode. The gas efficiency at rated conditions is 126 percent (on gas HHV) in heating mode. As a general efficiency feature, in moderate climate areas (about twice the heating load versus cooling load) the gas savings during the heating season can offset the gas consumption normally required by a considerable amount.
The homeowners were understandably a little nervous about utilizing this new technology, but Falade reassured them that if they were unhappy with the heat pumps, he would reconfigure the system and install something else. The homeowners gave the go-ahead, and Falade ended up installing two 5-ton absorption heat pumps.
The two units are controlled by a Robur direct digital control (DDC) board, which Falade explains, operates them as a plant instead of separate units. “It stages them as needed, evens out run time between them, and offers a multitude of other functions. The manufacturer is currently working on an upgrade that will allow me to communicate with the DDC directly from my office computer.”
WARM FLOORSThe radiant system is connected to the heat pumps, which provide a continuous supply of 110° water. Only the floors in the traffic areas are warmed, including the bathrooms (and tub surround), kitchen, and foyers, as well as the basement and three-car garage. The radiant system is limited by thermostats but will run continuously at lower outdoor temperatures. It effectively heats the living areas of the home until the outdoor temperature reaches about 20°. Once the air temperature in any given zone drops below 70°, the thermostat in that zone will turn on its respective air handler, which in turn will call for warm water from the heat pumps. All air handlers are set to low fan speed, which serves to minimize noise from the distribution system (the owners had specified that the system be low noise).
Having the radiant heating system operate off the heat pumps dramatically increases their efficiency, noted Falade. “The radiant is really where you save your money, especially if the house is well insulated like this house is. You can turn the water temperature way down and still get a nice, consistent temperature in the house. That’s really the secret: The lower you can go with the supply water temperature and keep your customer comfortable, the less money they’re going to spend on fuel.”
Falade also liked the ease with which he could connect the radiant heating system to the heat pumps. “I didn’t have to use any mixing valves anywhere. The water comes straight out of the units at 110°, and the heat pumps don’t care what temperature the return water is.”
Nine programmable thermostats control six air handlers, and there are three radiant heating sensing thermostats, which zone the first, second, and third floors. The basement and garage both have air-sensing programmable thermostats, which were set to boost the temperature in those spaces 1° from 11 a.m. to 5 p.m. This causes the heat pump system to store heat in the concrete during the warmest part of the day, which is when the air-source system runs most efficiently.
Since this was the first time Falade installed this type of heat pump, there was a bit of a learning curve; however, he and the homeowners are both very happy with how the project turned out.
“I would absolutely install these systems again. Of course, the next time, I would do things differently. For example, this time I sized it by the book, but on the next one, I will increase the size of all the tubing feeding the air handlers and floor manifolds, because bigger tubing means smaller pumps, which means less electricity used. There are also new developments in the variable-speed pump arena, which hold possibilities for even more savings on the electrical side.”
Everyone is interested in energy savings these days, so it’s likely there will soon be more homeowners interested in having natural gas-fired absorption heat pumps installed in their homes.