A heat pump is, very simply, a device that moves heat from one place to another: outside to inside, or inside to outside. By using a compressor, which is similar to an air conditioning unit, we can take heat from colder air (or water) which comes into the system as a vapour, compress it (which adds heat) and then deliver that heat to our system. Our heat pumps are generally designed to heat water. That water can be used for floor heating, air heating and domestic hot water.
Most North American heat pumps are typically designed to heat air. They are generally based on standard air conditioners with a few changes that allow them to move the heat in the other direction. This doesn’t make for a highly evolved system, and a backup furnace is often needed. Some people design systems to switch over to the furnace at temperatures as high as 0°C. The backup can be either electric heat strips or a separate gas or oil furnace. We believe a good heat pump should be able to give good performance down to -15°C, below which temperature some backup will be necessary. Of course, this is dependent on the home and its location. Some situations need no backup.
We model our heat pumps after systems that have been in use for decades in Sweden, Norway, Denmark, Germany and Austria. These systems all heat water and then use the water to heat floors, radiators or, very occasionally, air. One reason for picking floor heating as a first choice is based on the COP (coefficient of performance) of the unit. The higher COP the better. To get a high COP over the entire heating season (we sometimes use the term HSPF for the seasonal performance), we need to keep the difference between the supply temperature (outside air or ground temperature) and the delivery temperature (floor temperature needs) as small as possible.
With a GSHP (ground source heat pump or geothermal) we can have a ground supply temp averaging 5°C and a delivery temp to the floor of 30°C (optimal conditions). This will allow for a COP of close to 5 with our equipment. In other words, for every kw of electrical energy consumed by the HP, the system can deliver 5kw of heat to the floor.
Air source heat pumps (ASHPs) operate in the same way as GSHPs except that the heat is taken from the outside air rather than the ground. ASHPs are much less costly than GSHPs because there is no well drilling involved. While the installed cost is much lower, the annual COP of the system will also be a bit lower due to the varying temperature of the outside air. If the outside air temp is higher than the ground temp, the ASHP will be more efficient than a GSHP but when the temp is lower, the efficiency is also lower. There are ways to minimize the energy consumed, including using solar so that an ASHP can be more efficient annually than a GSHP. When heating water and using it with floor heating, we are also able to take advantage of time of use electrical rates to further reduce heating costs. This is why it is easier to heat water than air with a heat pump.
By adding solar hot water to the mix we can decrease the amount of energy used year round by providing direct solar heat for domestic hot water in the warmer months and increasing the supply temperature to the HP in the winter months, thereby increasing the system performance. Depending on the number of solar panels attached, the COP of the system can be considerably higher than 5.
We are now designing systems around the Ecologix heat pump line. These cold climate heat pumps (CCHP) are designed and built in Ontario and come in air to air units and air to water units which we use for heating floors and radiators.
The picture at left, with the brick wall, shows the outdoor evaporator part of the heat pump in a residential application. The compressor and controls are in the basement as is the buffer tank which is used to store the heat. An update (Jan 2015) on the HP installed: After nearly one year, the A2W heat pump has provided full heating when the weather is -10C or above. Only below this temperature is the back up boiler needed. The home is insulated and air sealed to reasonable standards of 25 years ago but certainly not for todays standards. With some extra insulating and air sealing work, this heat pump could provide for the entire heating needs. Given that it is providing heat to old cast iron radiators, we feel that it has excellent performance.
Shown at right is another evaporator. This one is providing heat (or removing heat) from a climate simulator at George Brown College. We installed the heat pump with Building Science Consulting of Waterloo who engineered and built the simulator. The system is designed to be able to simulate outdoor conditions of colder than -20°C and indoor conditions of 20°C in order to test the effectiveness of various wall, window and door structures. The chamber can also simulate 40°C outdoor temps to test for cooling loads.
Shown at left is the climate chamber with the outdoor climate through the door on the right and the indoor climate through the door on the left. The parts can be separated to access and make changes to the wall structure being tested.
We also carry the Fujitsu line of high efficiency ductless heat pumps. These are useful when the heat load of the area is low enough or the area is open concept. In the right conditions, an ductless ASHP can be used on each floor of the house. A Fujitsu HP is being used to in the above climate chamber to maintain the 20°C indoor comfort level.