It is only the heat pumps which are able to heat while at the same time to cool. For these appliances the low-range-temperature heating and high-range-temperature cooling are considered convenient. The efficiency, the performance index of these heat pumps, grow exponentially, with the approaching evaporation and condensation temperature. Heat pumps operate at their full capacity (especially within the range of cooling, refrigerating) exclusively at a fraction of its entire operating time. Most of the time they operate at a half capacity, load. That is why the attention of an investor is to be focused not only on the overall efficiency at the maximum thermal load, but at the same time on the seasonal efficiency which incorporates the ability of the refrigeration circuit to adapt to the partial load.
Division of heat pumps
A heat pump is to be understood as an appliance which uses low-temperature energy gained from the outer environment, the access to which around us is almost unlimited. The heat is drawn from the air, soil (ground-coupled heat exchanger, ground to water heat pump, geothermal heat pump, geothermal bore) and water, while at the same time the heat is dissipated from the lower temperature level to the higher temperature level. The heat pump does not generate energy, it only re-pumps it onto the higher heat level, while consuming a certain amount of electrical energy. Heat exchangers use cca 1/4 of electrical energy, the rest is transferred heat.
Figure Description: PRINCIPLE OF HEAT PUMP OPERATION (Outside environment energy 3/4), compression, driving force (electrical energy 1/4, Heat radiated into the heating system 4/4, Expansion, Evaporation, Condensatio
The principle of operation in the heat pump
The COP index (coefficient of performance) speaks on the efficiency rate of any heat pump – heating factor. This is considered to be the performance output of a given appliance respecting precisely specified temperatures of both the primary and secondary circuit, so for instance, evaporation temperature and condensation temperature, eventually the outside temperature and the temperature of the heating medium. The overall performance of the heat pump shall not be understood as a constant value, however the overall performance rate changes observing the operating conditions. The most important for the overall heating rate of the appliance is a nominal cooling capacity of a given compressor which depends on the overall output, power rating of an electric motor, structural design of the compressor in question and the temperatures of heat carrying media of the primary and secondary circuits.
The overall coefficient of performance – COP ranks among dimensionless index values, hence it is represented using a number. The most common scenario is to represent the COP – heating factor (heating seasonal performance factor HSPF) or the coefficient of performance within the interval of 2 and 5. At any rate, the given figure representing the heating seasonal performance factor – HSPF it is a theoretical value, the real one, so called annual heating factor, quite commonly remains within the range of COP 2 – 3,5. For instance the heating season in Slovakia is, considering the date of long-term temperature average of outside temperatures, say 230 days with a mean temperature during days when heating is indispensable at 4,6 degrees Celsius. Why are theoretical and real heating factors so diversified? The real heating factor, has to incorporate into its value all the other energies, like electrical energy needed for the correct operation of the heat pump and not solely the consumption of electricity needed for operating the compressor. The temperature of heated water is therefore the most important factor for the overall performance and efficiency of a given appliance.
Heat pumps air – to – water
Recently, one of the most widespread type of a heat pump. Gaining thermal energy from the air is considering the installation and the resultant operation the easiest and not rarely financially speaking the least demanding solution. The air is everywhere at all times – omnipresent. A hidden disadvantage though is an extensive range of temperatures when relating to ever changing seasons and very low temperatures in the winter season. Current heat pumps operate with a very high efficiency rate up to the range of temperatures between -25 degrees Celsius and + 35 degrees Celsius. We know two types of these heat pumps, namely SPLIT and KOMPAKT. The most common heat pump supplied is the one of the SPLIT type. Out company has been supplying the Slovak market with a unique system of the heat pump, being equipped with a fully-equipped control room/operation panel/ancillaries. This system requires approximately 1 square metre of the floor-plan area within the facility/unit concerned.
This very heat pump may be paired to for instance hot-water stove, fireplace, solid fuels boiler, gas boiler and all that to be assembled as an all-in-one unit. This system of assembly enables the heat pump to heat the water both for the central heating as well as for hot utility water preparation. On the other hand it is unable to cool and air condition premises. Should you wish to use the heat pump for cooling the interiors of buildings – for instance cooling ceiling, it is necessary to use a heat pump equipped with a hydro module. This appliance may consequently either heat or cool.
Heat pumps earth – to – water
These types of heat pumps collect low potential energy from earth.
Horizontal collectors are placed horizontally under the top-soil surface in the depth of between 1,2 – 1,5 metres. They collect heat from the ground and consequently they distribute the heat by means of heat-carrying medium (water – ethylene glycol) to the heat pump. This system is very demanding considering the overall area needed for the collector, the area needs to be twice to three times larger than the intended area of the building to be heated.
Geothermal wells, vertical bores
Geothermal probes / sondes (a pair of pipes, eventually more) are placed in the bore in the depth of 50 – 100 metres, of which by means of the heat carrying medium (water – ethylene glycol) the heat is collected and distributed from the earth into the heat pump. Geothermal wells, vertical bores or the resulting installations do require little space, and are less space-demanding, while at the same time they are more stable in comparison with the horizontal collectors. Absorption capacity of the geothermal probes / sondes differ depending on the terrain and ranks between 30 to 100 Watts per one metre of geothermal area.
The most efficient of all the heat sources is the ground water whose temperature remains stable and respecting the seasonality in the weather it remains almost constant, which ranges between 8 – 14 degrees Celsius. With these temperatures the heat pump achieves even higher performance rating, with the lower consumption and that in effect means saving on the operating costs, overheads, in comparison with the earth collector – ground loop, vertical probe / sonde, or geothermal well. The principle rests with pumping the ground water from the collection point (well) into the heat pump, where the heat energy is trapped and as a matter of fact it is later recirculated back into the entrapment bore (well). The distance of the bores depends on a given crust layers and the amount of pumped water, so as both the bores remain intact and mutually uninfluenced. With common family houses the recommended distance represents at least 10 metres.