Heat pump called the mechanical device that allows us to transfer energy from one area of low temperature to an area of higher temperature.
Already by the definition, it is apparent that heat pumps are designed to transfer heat (thermal energy) in a direction opposite to the natural flow. To transfer requires energy.
(Just as in hydraulics, water goes alone (flow) from a high point at the low (due to gravity) and need a pump to transfer the water unlike the natural flow (to move higher), so the thermal energy "flows" itself from high body temperature (warm) to lower body temperature (cold) and we need a "heat pump" to reverse the movement of energy and the transfer of the low temperature (cold) in high (hot).
Principle of operation of heat pumps
Heat pumps work in the same way they work all coolers and their operation is based on the same principles that apply to refrigerators, freezers, air conditioners, etc. Their operation is based on refrigeration cycle, which is a continuing cycle of expansion and compression of a fluid (working fluid) according to the following schedule:
The fluid (refrigerant) flowing through the tubes, in position 1, is liquid at high pressure and temperature, after the compressor. In position 1, the heat discharged during the compression afforded by the compressor. Then, the refrigerant is expanded (reduced pressure) in the expansion valve (2), and evaporated (because of the pressure drop) to the evaporator in position 3, where it is cooled and employs heat. Then the cold coolant, even in gaseous form, is compressed in the compressor is condensed, heated, eliminates heat and so forth.
The important thing is that in each cycle, heat is rejected (energy) at position 1 and recruited (energy) in position 3, so if the cycle is continuous, there is a continuous transfer of heat from point 3 to point 1, and therefore the refrigeration cycle can to transfer heat (energy) between two points.
This function (the transfer of heat from one point to another) is given the name "heat pump" devices operating on the cooling cycle.
Types of heat pump
Depending on the fluid which eliminate (or which engages) the pump energy in (1) and (3) of the refrigeration cycle, heat pumps are classified into:
1. Heat pumps air / air
Pumps are available in point 1 and point 3 heat exchanger air / coolant. It is known to all of us split type air conditioners (split type). Especially in divided form one element (heat in position 3) is in our house and hires energy (removes heat / cool the room), and elsewhere (1) also exchanger coolant / air and expels heat out of the our house.
2. Heat pumps air / water.
These pumps on one side (point 3) instead of element having heat coolant / water and remove heat (cool) water instead of air. With these pumps that we can draw heat (and thus cooled) water and excreted into the environment (as is done in air conditioners as above).
3. Heat pumps water / water.
Such pumps and two heat exchangers is water, and the refrigerant transfers heat from one body of water to another. Such pumps are water cooled heat pumps and cooling tower water pumps / water used in installations with ground heat exchanger (geothermal).
Depending on the position of the various components, heat pumps are classified into:
Uniform or autonomous (Compact) where all mechanisms are in public housing.
Split type or bilateral (Split units). The evaporator (or condenser) is independent of the rest of the system.
Depending on the type of prime mover, heat pumps are classified into
Pumps with electrically driven compressors
Pumps and compressors driven by internal combustion engines (diesel, steam, gas, etc.)
Pumps and compressors sorption (thermal energy of low and medium temperature).
Efficiency of heat pumps
The energy flow in a heat pump operating in heating mode, is as shown below:
The pump draws from a cold environment amount of heat (energy) Q1, adds mechanical work (W) compressor and delivers energy amount Q2 the cold.
When the pump is operating in heating mode, the "hot" is a space, a "cold" environment, and the goal is Q2, while when it operates in cooling mode, the "cold" is a space, a "hot" the environment and the goal is Q1.
The energy balance in shape requires
Q2 = Q1 + W.
Efficiency in heating mode
The ratio of heat transferred to the work consumed (Q2/W heating), called special efficiency pump (COP, coefficient of performance).
Efficiency in cooling mode
The ratio of heat transferred to the work consumed (Q1/W in cooling), called Energy efficiency pump (EER, energy efficiency ratio).
Both the specific efficiency COP and the energy efficiency ratio EER dependent:
- The temperature of the "source" (TQ1)
- The temperature of the "recipient" (TQ2)
- The mechanical characteristics of the heat pump
- The properties of the working medium.
and constantly changing, since both the temperature of the cold (ambient heating - space cooling) and the temperature was warm (space heating - cooling environment) are not fixed, but can change constantly.
To evaluate the energy efficiency of heat pumps has been established to measure the COP and EER at standard conditions (conditions Eurovent) which are:
Temperature = 20 ° C and hot
Outside air inlet temperature 7oC / 6oC WB (Cold)
and the cooling
Temperature = 27oC and hot
Outside air inlet temperature 35oC / 6oC WB
The efficiencies at Eurovent conditions characterize the quality of construction of a heat pump, since their calculation refers to the same conditions for all pumps.
However in actual operating conditions of a heat pump temperatures are not equal to the temperatures specified in the standard Eurovent, and define the average or annual special efficiency SCOP (for heating) and the average annual level or energy efficiency SEER (for cooling operation ) which is essentially the average efficiencies of a heat pump in annual operation and these points are the best criterion for assessing the energy efficiency of a heat pump.
Modern heat pumps meet EER and COP values ??greater than 3.0, which classifies devices using renewable sources. Price COP (or EER) equal to 3.0 means that for every unit of energy consumed by a heat pump transfers (attributes) to three (3) units of energy.
Heat pumps for domestic use
In recent years, the rapid development of technology has allowed the construction of inverter heat pumps high efficiency and small size at a reasonable cost of production.
The continued increase in fuel prices traditionally used for heating homes (oil, natural gas, etc.) in conjunction with the ever decreasing cost of heat pump makes the "household" heat pumps now an attractive option for heating of the modern house.
Domestic heat pumps start at sizes close to 6kW, reaching up to 20kW, and can meet the needs for heating and hot water production for applications in small apartments, townhouses and small buildings.