Do-it-yourself heat pump: circuit features, efficiency and payback period

A heat pump (HP) is an innovative, efficient, ecological and budgetary solution for generating heat for the needs of hot water supply (DHW) and heating. The principle of its operation is simple. The device takes heat from natural environments (air, earth, water) and supplies it to the heating system (OS) and hot water supply.

The internal heat carrier (ammonia or other refrigerant) takes energy from the environment and transports it to the evaporator. In him refrigerant is converted from liquid to gas by evaporation. At the next stage, the volume of the gaseous heat carrier decreases and, therefore, its temperature rises.

The hot coolant circulates in the condenser, the heat release from which enters the heating system of the house. The expansion valve recools the refrigerant and starts a new heat cycle, creating an extremely efficient heating system.

Heating source connection diagrams and efficiency

The efficiency of such a pump is determined by comparing the amount of energy generated by the device and the amount of electricity consumed for its own needs. First of all, it depends on the outside temperature. In heating mode system performance dropswhen the outside temperature drops. In cold climates at the lowest possible temperatures, such a system requires additional backup heating when it alone cannot provide enough heat to maintain the sanitary temperature of the air in the room.

There are different heat sources for heating systems:

• Air;
• The soil;
• Groundwater.

Simple calculations show that if a highly efficient natural gas boiler can operate with efficiency of 93%, TS "air-to-air" - by 180%, and TS "ground-water" can achieve efficiency up to 400%.

Water-to-water heat pumps

Water-to-water pumps convert the energy obtained from natural water sources for the in-house heating circuit. Hydrothermal systems use groundwater for the needs of:

• heating the building;
• cooling the building;
• Domestic hot water supply;
• heating water for swimming pools.

Pumps extract heat energy from groundwater using boreholes, drainage systems and other water systems. The received energy through the heat transfer system is given to the water circulating in the heating system of the house. Chilled water returns to the aquifer horizon through the discharge well. The efficiency of hydrothermal systems with water HP is ensured by the constant temperature of groundwater throughout the year, usually at the level of 8-13 C.

These conditions create a stable high-performance heating system and make it independent of external weather conditions. Therefore, water-to-water pumps are the most efficient and have a guaranteed constant coefficient of performance (COP). COP shows the ratio of heat energy (kw) to the electricity consumed by the heat pump (kw) for own needs to provide heating of the building.

When the temperature is between 8-13 C and the supply temperature is is 35 C, COP coefficient = 5 ÷ 7. In this case, for each kilowatt of electrical energy spent on HP control, we get free energy 5 ÷ 7 kwsufficient to maintain a sanitary thermal regime in a room with an area of ​​approximately 60 m².

The industry produces a wide range of water-to-water pumps, which are successfully used in heat supply systems and air conditioning of low-rise single-family and multi-apartment buildings, as well as hotels, schools, office buildings and industrial facilities. A limitation in the use of this type of HP may be the availability of permits for the installation of a well.

Application of geothermal systems for heat supply

The use of geothermal energy (near-surface) is another effective area of ​​pumping. A pipe system with a length of about 100 meters is being laid underground, which accumulates the heat of the soil. Soil condition determines how many geothermal systems it is necessary to ensure the heating load of the house. In the case of large areas, heat from nearby underground collectors from district heating or water supply can be used as an alternative.

The heat pump circuit works great in the summer in air conditioning mode. After collecting heat from the ground, this energy is taken by a pump and supplied to the building's internal heating system. Ground source pumps require a higher investment in installation than air pumps, but they provide constant heating power because the soil has constant temperatures throughout the year. In this way, continuous energy production is guaranteed.

How to install a geothermal system? Installing a geothermal system can go in several directions:

1. The heat exchanger pipes are located horizontally, have a trench length of hundreds of meters. Such a scheme requires a significant amount of earthwork and leads to a violation of the local landscape. In addition, in the future, this piece of land will be problematic to use for perennial green spaces.
2. The heat exchanger pipes are arranged vertically, loops up to 10 meters. The most time consuming and expensive option.
3. The heat exchanger pipes are located under the water of a reservoir located near the house. The cheapest option.

Advantages:

1. Infinitely variable compressor modulation for an overview of monitored capacity.
2. Reduced energy consumption and costs compared to conventional heat pumps.
3. High energy efficiency.
4. Longer service life thanks to the soft start procedure.
5. Heating temperature at the outlet up to 60 C.
6. COP> 7.
7. Significantly lower operating costs thanks to an intelligent cooling cycle.

In addition to significant cost savings, the geothermal system has some additional benefits. Heat is generated at a lower temperature than forced air and works continuously, therefore the system is more stable, does not have large temperature differences.

Geothermal systems lend themselves well to automation with unloading of heating power. When the temperature in the room corresponds to the parameters set by the consumer, excess heat will go to other tasks of energy exchange, for example, for heating hot water. The typical payback period for most geothermal systems is 5-10 years, which is comparable to the payback period for solar energy.

Air split systems

For this type of pump, the source is energy from outside air. The main advantage of air heat pump in comparison with geothermal and water heating is the low cost of installation, since no excavation, installation and deep-sea laying works are required heat pipelines.

Air heat pumps are available for outdoor and indoor installation, made in monoblock or split systems. For monoblock air pumps, the plate heat exchanger is located in the outdoor unit and energy is supplied to the indoor unit through well insulated heat pipes. With a split heat pump, the heat exchanger is located in the indoor unit so that energy is transported inward through the refrigerant.

One limitation: HPs with an air source lose efficiency in colder weather and stop working when the temperature drops below -20 degrees, therefore, for regions with an average temperature of cold air no more than -10 C, such systems are the most preferred.

Calculation of the heating circuit

The first thing to do before installing a heat pump is to calculate the heat balance of the house. This will allow determine the heat transfer required to ensure required comfort temperature. When sizing the pump, the following data should be taken into account:

• the purpose of the building;
• its total area;
• the number of floors, the area of ​​each of them;
• ceiling height;
• desired (required) room temperature;
• walls (material, layer thickness);
• type and total glazing area;
• the presence of a ventilation system and its characteristics;
• hot water demand, number of points;
• heaters and their type;
• presence / absence of land / water nearby;
• presence / absence of restrictions on electricity.

You can quickly pre-calculate your home's energy needs using the formula:

P = V x C x T,

where V is the volume of housing in m 3;

C - construction factor C = 0.75 if the house is very well insulated (RT2005) C from 0.9 to 1.3 when the house is poorly insulated C = 1.6;

T is the difference between the required temperature in the house and the lowest outdoor temperature during the cold season for the geographical area of ​​the building location.

Example: A house with an area of ​​200 m², a height of 2.5 m, located in the Moscow region, the temperature inside the room is 20 C, the outside temperature is 16 C. P = 200 x 2.5 x 0.9 x (20 - (-16)) = 16200 W

For this home that requires 16 kw, we need a heat pump with a capacity of 16 kw up to 20 kw .

Manufacturing a heat pump for household needs

It is profitable and convenient to make a heat pump for heating a house with your own hands. Statistics claim that TN for a house with an area of ​​200 m² will pay off within the first three yearsAnd this is not the limit, given the growing cost of fuel and electricity. You can reduce these costs if there are craftsmen in the house who can assemble a pump from scrap materials. For this you will need:

1. Powerful compressor, for example for an air conditioner. If there is no such thing at home, then you can pick it up in the repair shops for refrigerators and air conditioners. For it, you first need to prepare the mount in a convenient place (usually on the wall of the house).
2. Capacitor, you can make it yourself. Make a coil from a copper tube with a wall thickness of at least 1 mm, which is placed in a welded metal body of a suitable size. Install the necessary taps and connections on it. It is also placed on the wall next to the compressor. In order for the coil to be made with high quality, the copper pipe is wound, for example, on a gas cylinder, and the turn-to-turn distance is fixed with an aluminum corner. Final installation of the condenser (brazing copper pipe, pumping freon, etc.) ) it is better to entrust it to a professional so as not to damage the VT and not get injured during assembly or operation.
3. Evaporator - a container for converting a liquid refrigerant into a vapor state. The resulting steam enters the compressor, which pumps it under pressure to the condenser.
4. Throttle valve. It is necessary to purchase, taking into account the parameters of the pump.
5. Connecting pipe elements of the diagram depending on the selected type of installation.
6. Check the hydraulic tightness of pipeline systems by pressure testing (air or water).
7. They check the reliability of the power equipment at home.

Advantages and disadvantages of a heat supply source

Benefits of heat pumps:

• Ideal electric heating: production of 4 kW of heat with a consumption of 1 kW for the plant's own needs.
• Independence from expensive fuel (gas, coal, fuel oil).
• Efficient energy balance complete with floor or wall heaters.
• They take up little space in a house or basement.
• Low maintenance costs.
• It integrates well into the "smart home" system.

Disadvantages:

• The economic efficiency after practical tests in old houses does not always correspond to the declared by the equipment manufacturer.
• High demands on the heating system.
• The presence of a storage tank in the circuit.
• The temperature of the heat source is constant only with groundwater.
• Many models contain a climate-damaging refrigerant.