A leading London University installed eTRV+ with PAIR in their student halls of residence and made energy savings of 30%. The University had been using their building management system to control the heating, with temperature control via TRV’s in each bedroom, the kitchen and corridors. The system provided two heating periods, switching on in the morning and evening and remaining off in the afternoon and overnight. eTRV+ was initially fitted in student’s bedrooms, and then extended into corridors and kitchens to provide balanced temperature control throughout the building. Bedrooms and were set to 19°c, with the boost facility to 21°c. Corridors were set to 16°c and kitchens to 19°c. PAIR was installed in bedrooms to detect occupancy. If a student left their room for longer than one hour, eTRV+ would decrease the temperature to the low setting (16°c). eTRV+ includes a Sleep facility, that provides the option to reduce heating further during longer period...

Geothermal heat pumps (GHPs), sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat pumps, have been in use since the late 1940s. They use the relatively constant temperature of the earth as the exchange medium instead of the outside air temperature.  Although many parts of the country experience seasonal temperature extremes -- from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of these more favorable temperatures to become high efficient by exchanging heat with the earth through a ground heat exchanger. As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, an...

Ductless, mini-split-system heat pumps (mini-splits) make good retrofit add-ons to houses with "non-ducted" heating systems, such as hydronic (hot water heat), radiant panels, and space heaters (wood, kerosene, propane). They can also be a good choice for room additions where extending or installing distribution ductwork is not feasible, and for very efficient new homes that require only a small space conditioning system. Be sure to choose an ENERGY STAR® compliant unit and hire an installer familiar with the product and its installation. Like standard air-source heat pumps, mini-splits have two main components -- an outdoor compressor/condenser and an indoor air-handling unit. A conduit, which houses the power cable, refrigerant tubing, suction tubing, and a condensate drain, links the outdoor and indoor units.

Heat pumps can have problems with low airflow, leaky ducts, and incorrect refrigerant charge. There should be about 400 to 500 cubic feet per minute (cfm) airflow for each ton of the heat pump's air-conditioning capacity. Efficiency and performance deteriorate if airflow is much less than 350 cfm per ton. Technicians can increase the airflow by cleaning the evaporator coil or increasing the fan speed, but often some modification of the ductwork is needed. See minimizing energy losses in ducts and insulating ducts. Refrigeration systems should be leak-checked at installation and during each service call. Packaged heat pumps are charged with refrigerant at the factory, and are seldom incorrectly charged. Split-system heat pumps, on the other hand, are charged in the field, which can sometimes result in either too much or too little refrigerant. Split-system heat pumps that have the correct refrigerant charge and airflow usually perform very close to manufacturer's listed SEER and HSPF. T...

Every residential heat pump sold in this country has an EnergyGuide label, which displays the heat pump's heating and cooling efficiency performance rating, comparing it to other available makes and models. Heating efficiency for air-source electric heat pumps is indicated by the heating season performance factor (HSPF), which is a measure over an average heating season of the total heat provided to the conditioned space, expressed in Btu, divided by the total electrical energy consumed by the heat pump system, expressed in watt-hours. Cooling efficiency is indicated by the seasonal energy efficiency ratio (SEER), which is a measure over an average cooling season of the total heat removed from the conditioned space, expressed in Btu, divided by the total electrical energy consumed by the heat pump, expressed in watt-hours. In general, the higher the HSPF and SEER, the higher the cost of the unit. However, the energy savings can return the higher initial investment several times during ...

A heat pump's refrigeration system consists of a compressor and two copper or aluminum coils (one indoors and one outside), which have aluminum fins to aid heat transfer. In heating mode, liquid refrigerant in the outside coil removes heat from the air and evaporates into a gas. The indoor coil releases heat from the refrigerant as it condenses back into a liquid. A reversing valve, near the compressor, can change the direction of the refrigerant flow for cooling mode as well as for defrosting the outdoor coil in winter. The efficiency and performance of today's air-source heat pumps is a result of technical advances such as the following: Thermostatic expansion valves for more precise control of the refrigerant flow to the indoor coil Variable speed blowers, which are more efficient and can compensate for some of the adverse effects of restricted ducts, dirty filters, and dirty coils Improved coil design Improved electric motor and two-speed compressor designs Copper tubing, groo...

The different types of air source heat pumps are described below. Ductless vs. Ducted vs. Short-Run Ducted Ductless applications require minimal construction as only a three-inch hole through the wall is required to connect the outdoor condenser and the indoor heads. Ductless systems are often installed in additions. Ducted systems simply use ductwork. If your home already has a ventilation system or the home will be a new construction, you might consider this system. Short-run ducted is traditional large ductwork that only runs through a small section of the house.  Short-run ducted is often complemented by other ductless units for the remainder of the house. Split vs. Packaged Most heat pumps are split-systems—that is, they have one coil inside and one outside. Supply and return ducts connect to the indoor central fan. Packaged systems usually have both coils and the fan outdoors. Heated or cooled air is delivered to the interior from ductwork that passes through a wall or...

An air-source heat pump can provide efficient heating and cooling for your home. When properly installed, an air-source heat pump can deliver up to three times more heat energy to a home than the electrical energy it consumes. This is possible because a heat pump transfers heat rather than converting it from a fuel like combustion heating systems. Air heat pumps have been used for many years in nearly all parts of the United States, except in areas that experienced extended periods of subfreezing temperatures. However, in recent years, air-source heat pump technology has advanced so that it now offers a legitimate space heating alternative in colder regions. For example, a study by the Northeast Energy Efficiency Partnerships found that when units designed specifically for colder regions were installed in the Northeast and Mid-Atlantic regions, the annual savings are around 3,000 kWh (or $459) when compared to electric resistance heaters, and 6,200 kWh (or $948) when compared to oil sy...

A number of innovations are improving the performance of heat pumps. Unlike standard compressors that can only operate at full capacity, two-speed compressors allow heat pumps to operate close to the heating or cooling capacity needed at any particular outdoor temperature, saving energy by reducing on/off operation and compressor wear. Two-speed heat pumps also work well with zone control systems. Zone control systems, often found in larger homes, use automatic dampers to allow the heat pump to keep different rooms at different temperatures. Some models of heat pumps are equipped with variable-speed or dual-speed motors on their indoor fans (blowers), outdoor fans, or both. The variable-speed controls for these fans attempt to keep the air moving at a comfortable velocity, minimizing cool drafts and maximizing electrical savings. It also minimizes the noise from the blower running at full speed. Some high-efficiency heat pumps are equipped with a desuperheater, which recovers waste hea...