Heat Pump pump heat from one location and return it to another. That's why, that logically, it is called a "heat pump". All heat pumps operate basically on the same principle. This is a circuit of a liquid that "brings the heat: condensation. When forced to evaporate, it takes the heat that surrounds it. You know this principle is that of sweat. You sue because evaporates, the water is cool. Then forces the liquid condensate in the tablet (that is why heat pumps have a compressor) to liquefy. In doing so, it restores the heat he has taken to another place to evaporate. For a house, it is clear that it is interesting to cool the outside if it is to heat the interior. For a fridge in the kitchen, the refrigerator cools its interior by heating the kitchen! 

If it takes heat to evaporate a fluid is that its molecules are very attracted by each other. To take off a few, must be shaken very hard, so warm. Or in any case, when a molecule leaves the liquid, it is banged by neighbors who eject. Once the molecule part, his former neighbors least segment they used their energy to eject the molecule. So they are less hot. Evaporation cools it. 

Conversely, when a gas molecule occurs in a fluid, it is attracted by its neighbors. Suddenly, just when it happens, it becomes even more speed (because it is drawn) and it will knock her new neighbors. That the coup sagment more condensation (from gas to liquid) provides the heat. 

That's how it works! 

For the moment, most heaters operate using energy (electrical in the case of electric heating, or chemical in the case of heating oil or gas) and the dissipating completely. That is to have heat, we burn oil or gas and electricity increases in resistance to it is transformed into heat. And to be honest, it's a beautiful mess. Because this energy could be used to power a heat pump! 

The gas contains energy "chemical". When you burn 1 Joule gas or fuel oil (that is, a unit of energy per kilowatt hour or calories) it provides 1 Joule heat your home. But if you use a heat pump for each Joule provided the pump, pump it between 3 and 7 to the outside! In short, it can provide you with up to 7 Joules of energy. Conclusion: for now, our way of heating reflects the fact that we have energy in abundance enough to waste it! But as it rique not last (it will take some years to consume 4 to 5 times less energy than today) many people might make the heat pump. It will become very profitable. 

It may seem paradoxical that a heat pump is still able to take the heat when it's cold outside (like 4 ° C). Yes, but in fact, everything depends on the scale that we take. When a body is hot, is that its molecules are agitated. If they are agitated because they have energy (ie kinetic). If the molecules of an object does not move at all, it is at absolute zero, 0 Kelvin. The Kelvin unit is the true temperature. In fact, 4 ° C corresponds to 273 4 = 277 Kelvin. While you, at 37 ° C, you are 273 +37 = 310 Kelvin. In fact, 4 ° C is really hot from that point of view. It contains a lot of heat, we can take. 

Heat pumps, you know: there are fridges, air conditioners (which take the heat inside to reject it out), also known as geothermal energy (in fact it is a pump heat that takes the heat in the soil). There are many kinds of heat pumps. One of the easiest to implement is a cooling in reverse, taking heat to outside air and return it to the inside. And it works not bad!

Heating and Cooling with a Heat Pump

Ground-Source Heat Pumps
(Earth-Energy Systems)

A ground-source heat pump uses the earth or ground water or both as the sources of heat in the winter, and as the "sink" for heat removed from the home in the summer. For this reason, ground-source heat pump systems have come to be known as earth-energy systems (EESs). Heat is removed from the earth through a liquid, such as ground water or an antifreeze solution, upgraded by the heat pump, and transferred to indoor air. During summer months, the process is reversed: heat is extracted from indoor air and transferred to the earth through the ground water or antifreeze solution. A direct-expansion (DX) earth-energy system uses refrigerant in the ground-heat exchanger, instead of an antifreeze solution.

Earth-energy systems are available for use with both forced-air and hydronic heating systems. They can also be designed and installed to provide heating only, heating with "passive" cooling, or heating with "active" cooling. Heating-only systems do not provide cooling. Passive-cooling systems provide cooling by pumping cool water or antifreeze through the system without using the heat pump to assist the process. Active cooling is provided as described below.
How Does an Earth-Energy System Work?

All EESs have two parts: a circuit of underground piping outside the house, and a heat pump unit inside the house. Unlike the air-source heat pump, where one heat exchanger (and frequently the compressor) is located outside, the entire ground-source heat pump unit is located inside the house.

The outdoor piping system can be either an open system or closed loop. An open system takes advantage of the heat retained in an underground body of water. The water is drawn up through a well directly to the heat exchanger, where its heat is extracted. The water is discharged either to an above-ground body of water, such as a stream or pond, or back to the underground water body through a separate well.

Closed-loop systems collect heat from the ground by means of a continuous loop of piping buried underground. An antifreeze solution (or refrigerant in the case of a DX earth-energy system), which has been chilled by the heat pump's refrigeration system to several degrees colder than the outside soil, circulates through the piping, absorbing heat from the surrounding soil.

The Heating Cycle

In the heating cycle, the ground water, the antifreeze mixture, or refrigerant (which has circulated through the underground piping system and picked up heat from the soil), is brought back to the heat pump unit inside the house. It then passes through the refrigerant-filled primary heat exchanger for ground water or antifreeze mixture systems. In DX systems the refrigerant enters the compressor directly, with no intermediate heat exchanger.

The heat is transferred to the refrigerant, which boils to become a low-temperature vapour. In an open system, the ground water is then pumped back out and discharged into a pond or down a well. In a closed-loop system, the anti-freeze mixture or refrigerant is pumped back out to the underground piping system to be heated again.

The reversing valve sends the refrigerant vapour to the compressor. The vapour is then compressed which reduces its volume, causing it to heat up.

Finally, the reversing valve sends the now-hot gas to the condenser coil, where it gives up its heat. Air is blown across the coil, heated, and then forced through the ducting system to heat the home. Having given up its heat, the refrigerant passes through the expansion device, where its temperature and pressure are dropped further before it returns to the first heat exchanger, or to the ground in a DX system, to begin the cycle again.

Domestic Hot Water

In some EESs, a heat exchanger, sometimes called a "desuperheater", takes heat from the hot refrigerant after it leaves the compressor. Water from the home's water heater is pumped through a coil ahead of the condenser coil, in order that some of the heat that would have been dissipated at the condenser is used to heat water. Excess heat is always available in the cooling mode, and is also available in the heating mode during mild weather when the heat pump is above the balance point and not working to full capacity. Other EESs heat domestic hot water (DHW) on demand: the whole machine switches to heating DHW when it is required.

Hot water heating is easy with EESs because the compressor is located inside. Because EESs have relatively constant heating capacity, they generally have many more hours of surplus heating capacity than required for space heating.

Cooling Cycle

The cooling cycle is basically the reverse of the heating cycle. The direction of the refrigerant flow is changed by the reversing valve. The refrigerant picks up heat from the house air and transfers it directly in DX systems or to the ground water or antifreeze mixture. The heat is then pumped outside, into a water body or return well (in the case of an open system), or into the underground piping (in the case of a closed-loop system). Once again, some of this excess heat can be used to preheat domestic hot water.

Unlike air-source heat pumps, EESs do not require a defrost cycle. Temperatures underground are much more stable than air temperatures, and the heat pump unit itself is located inside; therefore, the same problems with frost do not arise. 
Parts of the System

As shown in Figure 7, earth-energy systems have three main components: the heat pump unit itself, the liquid heat exchange medium (open system or closed loop), and the air delivery system (ductwork).

Ground-source heat pumps are designed in different ways. Self-contained units combine the blower, compressor, heat exchanger, and condenser coil in a single cabinet. Split systems allow the coil to be added to a forced-air furnace, and use the existing blower and furnace.

Figure 7: Components of a Typical Ground-source Heat Pump

Energy Efficiency Considerations

As with air-source heat pumps, earth-energy systems are available with widely varying efficiency ratings. Earth-energy systems intended for ground-water or open-system applications have heating COP ratings ranging from 3.0 to 4.0, and cooling EER ratings between 11.0 and 17.0. Those intended for closed-loop applications have heating COP ratings between 2.5 and 4.0, while EER ratings range from 10.5 to 20.0.

The minimum efficiency in each range is regulated in the same jurisdictions as the air-source equipment. There has been a dramatic improvement in the efficiency of earth-energy systems efficiency over the past five years. Today, the same new developments in compressors, motors, and controls that are available to air-source heat pump manufacturers are resulting in higher levels of efficiency for earth-energy systems.

In the lower to middle efficiency range, earth-energy systems use single-speed rotary or reciprocating compressors, relatively standard refrigerant-to-air ratios, but oversized enhanced-surface refrigerant-to-water heat exchangers. Mid-range efficiency units employ scroll compressors or advanced reciprocating compressors. Units in the highefficiency range tend to use two-speed compressors or variable speed indoor fan motors or both, with more or less the same heat exchangers.

Figure 8: Open System Earth-energy System Efficiency (at an entering water temperature of 10oC)

Figure 9: Closed-Loop Earth-energy System Efficiency (at an entering anitfreeze water temperature of 0oC)

Sizing Considerations

Unlike the outside air, the temperature of the ground remains fairly constant. As a result, the potential output of an EES varies little throughout the winter. Since the EESs output is relatively constant, it can provide almost all the space heating requirement — with enough capacity left to provide hot water heating as an "extra."

As with air-source heat pump systems, it is not generally a good idea to size an EES to provide all of the heat required by a house. For maximum cost-effectiveness, an EES should be sized to meet 60 to 70 percent of the total maximum "demand load" (the total space heating and water heating requirement). The occasional peak heating load during severe weather conditions can be met by a supplementary heating system. A system sized in this way will in fact supply about 95 percent of the total energy used for space heating and hot water heating.

EESs with variable speed or capacity are available in two speed compressor configurations. This system can meet all cooling loads and most heating loads on low speed, with high speed required only during high heating loads.

A variety of sizes of EESs are available to suit the Canadian climate. Units range in size from 0.7 kW to 35 kW (2 400 to 120 000 Btu/h), and include domestic hot water (DHW) options.
Design Considerations

Unlike air-source heat pumps, EESs require that a well or loop system be designed to collect and dissipate heat underground.


As noted, an open system (see Figure 10) uses ground water from a conventional well as a heat source. The ground water is pumped into the heat pump unit, where heat is extracted. Then, the "used" water is released in a stream, pond, ditch, drainage tile, river, or lake. This process is often referred to as the "open discharge" method. 

Another way to release the used water is through a rejection well, which is a second well that returns the water to the ground. A rejection well must have enough capacity to dispose of all the water passed through the heat pump, and should be installed by a qualified well driller. If you have an extra existing well, your heat pump contractor should have a well driller ensure that it is suitable for use as a rejection well. Regardless of the approach used, the system should be designed to prevent any environmental damage. The heat pump simply removes or adds heat to the water; no pollutants are added. The only change in the water returned to the environment is a slight increase or decrease in temperature.

Figure 10: Open System Using Ground Water from a Well as a Heat Source

The size of the heat pump unit and the manufacturer's specifications will determine the amount of water that is needed for an open system. The water requirement for a specific model of heat pump is usually expressed in litres per second (L/s) and is listed in the specifications for that unit. The average heat pump unit of 10 kW (34 000 Btu/h) capacity tends to use 0.45 to 0.75 L/s while operating.

Your well and pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements. You may need to enlarge your pressure tank or modify your plumbing to supply adequate water to the heat pump.

Poor water quality can cause serious problems in open systems. You should not use water from a spring, pond, river, or lake as a source for your heat pump system unless it has been proven to be free of excessive particles and organic matter, and warm enough throughout the year (typically over 5C) to avoid freeze-up of the heat exchanger. Particles and other matter can clog a heat pump system and make it inoperable in a short period of time. You should also have your water tested for acidity, hardness, and iron content before installing a heat pump. Your contractor or equipment manufacturer can tell you what level of water quality is acceptable and under what circumstances special heat-exchanger materials may be required.

Closed-loop Systems

A closed-loop system draws heat from the ground itself, using a continuous loop of special buried plastic pipe. Copper tubing is used in the case of DX systems. The pipe is connected to the indoor heat pump to form a sealed underground loop through which an antifreeze solution or refrigerant is circulated. While an open system drains water from a well, a closed-loop system recirculates its heat transfer solution in pressurized pipe.

The pipe is placed in one of two types of arrangements: vertical or horizontal. A vertical closed-loop arrangement (see Figure 11) is an appropriate choice for most suburban homes, where lot space is restricted. Piping is inserted into bored holes that are 150 mm (6 in.) in diameter, to a depth of 18 to 60 m (60 to 200 ft.), depending on soil conditions and the size of the system. Usually, about 80 to 110 m (270 to 350 ft.) of piping is needed for every ton (3.5 kW or 12 000 Btu/h) of heat pump capacity. U-shaped loops of pipe are inserted in the holes. DX systems can have smaller diameter holes which can lower drilling costs. 

Figure 11: Closed-Loop, Single U-bend Vertical Configuration

The horizontal arrangement (see Figure 12) is more common in rural areas, where properties are larger. The pipe is placed in trenches normally 1.0 to 1.8 m (3 to 6 ft.) deep, depending on the number of pipes in a trench. Generally, 120 to 180 m (400 to 600 ft.) of pipe are required per ton of heat pump capacity. For example, a well-insulated, 185 m2 (2 000 ft.2) home would probably need a three-ton system with 360 to 540 m (1 200 to 1 800 ft.) of pipe.

Figure 12: Closed-Loop, Single Layer Horizontal Configuration

The most common horizontal heat exchanger is two pipes placed side-by-side in the same trench. Another heat exchanger sometimes used where area is limited is a "spiral" - which describes its shape. Other horizontal loop designs use four or six pipes in each trench, if land area is limited.

Regardless of the arrangement you choose, all piping for antifreeze solution systems must be at least series 100 polyethylene or polybutylene with thermally fused joints (as opposed to barbed fittings, clamps, or glued joints), to ensure leak-free connections for the life of the piping. Properly installed, these pipes will last anywhere from 25 to 75 years. They are unaffected by chemicals found in soil and have good heat-conducting properties. The antifreeze solution must be acceptable to local environmental officials. DX systems use a refrigeration-grade copper tubing.

Neither the vertical nor the horizontal loops have an adverse impact on the landscape as long as the vertical boreholes and trenches are properly backfilled and tamped (packed down firmly).

Horizontal loop installations use trenches anywhere from 150 to 600 mm (6 to 24 in.) wide. This leaves bare areas that can be restored with grass seed or sod. Vertical loops require little space and result in minimal lawn damage.

It is important that the horizontal and vertical loops be installed by a qualified contractor. Plastic piping must be thermally fused, and there must be good earth-to-pipe contact to ensure good heat transfer, such as that achieved by Tremie-grouting of boreholes. The latter is particularly important for vertical heat-exchanger systems. Improper installations may result in less than optimum heat pump performance.