- Suitable equipment class
- Scope of application
- Heat pump problems
- Variety of configurations: split systems, monoblocks, rooftops
- Engineering Communication
- Duct air conditioners
Limitations in the choice of energy resources are not uncommon today, especially in areas of “young” development. If there are no other sources of energy in addition to electricity at the facility, air conditioners will not only be an excellent way to cool housing in the summer, but also provide high-quality and economical heating in cold weather..
Suitable equipment class
Not all air conditioners are suitable for use as heating appliances. There is a separate group of climate technology called heat pumps. In short, the key difference between such equipment is the ability to invert the direction of the refrigerant in the evaporator and compressor circuits. Thus, in summer mode, the installation takes away excess heat from the room atmosphere and dumps it outside, while in winter everything happens according to the reverse scheme.
The principle of operation of the air-to-air heat pump in winter and summer modes
The air is heated by a heat pump not by converting electrical energy into heat (as in the simplest air conditioners with a heating function), but by pumping heat from one medium to another. This is where the name of the equipment comes from: even in frosty weather, the air contains a certain amount of heat, which can be removed and directed inside the building to maintain a comfortable climate. But this principle works only under certain conditions, the main limitation is the temperature difference between the street and the room, as well as the temperature limits at which the working coolant, the coolant, can evaporate and condense..
Air heat pump device
By design, heat pumps are quite complex devices. On the one hand, the package includes a number of devices that provide reverse circulation of the heating circuit under the control of automation. This is a four-way valve, a specially designed expansion valve and a more complex system of channels through which the refrigerant circulates. On the other hand, a real heat pump is necessarily equipped with devices that help the main pump units to work in extreme conditions. All auxiliary equipment in the language of marketing is called a “winter kit”, it includes:
- compressor oil heater;
- radiators of special design, resistant to condensation and freezing;
- recuperation devices supplying the exhaust ventilation flow to the external heat exchanger;
- heated refrigerant injection system;
- special brand of refrigerant.
Scope of application
The main evaluation criterion for heat pumps is the thermal efficiency factor, otherwise called COP. This value is actually quite difficult to determine, it depends both on the degree of thermodynamic perfection – the real efficiency of the machine, taking into account all the transformation chains, and on the power of the low-potential energy source. These two factors tend to change, mainly depending on the current temperature difference, that is, the dynamics of COP change under various operating conditions is of real interest. In other words, the performance of an individual heat pump model is considered in accordance with the dominant thermal regime, and not according to the coldest five-day period. The savings gained from the installation during the period of moderate temperature differences should cover the costs of operating the convection and radiant sources in severe frost when the heat pump cannot operate..
Heat pumps are not only designed for domestic use. They do an excellent job of strong cooling in confined spaces: freezers or computer compartments. In Western countries, the practice of diverting a separate basement room under a refrigerator room with the subsequent transfer of heat to the outside in summer or to the flow of ventilation in winter is actively developing. These are the so-called bivalent heat supply systems, another particular case is the supply of air to an external heat exchanger, passed through a ground heat exchanger or a dry solar collector..
Heat pump problems
Heating systems based on air heat pumps are characterized by a high design complexity: it is required to determine not only the sufficient volume of energy inflow to replenish heat losses, but also the effective mode of operation, the number and location of the heating system nodes. At the same time, the number of units and the cost of the equipment involved should, of course, be minimal..
Usually, the result of errors in the calculation and installation of air heating systems is the appearance of cold zones in the room, as well as condensation of moisture on the glazing that does not have a thermal curtain. The locations of the indoor units must be determined according to the temperature and flow rate distribution diagrams provided by the manufacturer for standard heating modes. This task is especially difficult to accomplish, given that the introduction of each new heating source requires in different variations:
- installation of an additional external unit;
- laying the freon line to the external block;
- air channel gaskets.
Because of this, the final configuration of the heating system must be chosen once, often long before the start of the home furnishing work. This is all due to the extremely low suitability of heat pumps for modernization and the lack of a significant power reserve. It is extremely important to be able to determine in what cases it is more convenient and more profitable to use traditional heating devices than an inverter air conditioner. Last but not least, you should think about the operating resource of the heat pump: its most efficient operation will be at COP values above 2–2.3.
Variety of configurations: split systems, monoblocks, rooftops
For all its awkwardness, heat pumps have enough configurations to choose the most convenient equipment placement. Multisplit systems owe their appearance to the desire to preserve the appearance of buildings, as well as to provide a higher level of technological organization. The fundamental difference between such systems is the presence of a splitter and an automatic power control device in a sufficiently high range.
The next step in this direction was taken with the entry into the market of multi-zone VRF systems and, as a particular case, VRV systems. In civilian use, such systems are aimed at collective use, they allow the simultaneous connection of several dozen indoor units to one street installation, while the length of the freon line can reach hundreds of meters, and the height difference between the system elements can be up to 12 floors.
Heat pump VRV
The only strict limitation for heat pumps is the need to find an external evaporator outdoors, all other configuration changes are at the discretion of the technologist. This made it possible to act in the opposite direction, avoiding the use of freon lines or minimizing their length. Compact heat pumps for local heating are quite inexpensive and do not require connecting pipes or air ducts. Monoblock inverters built into a wall or window, as well as rooftops, the blocks of which are located on opposite sides of the roof overlap at a minimum distance, allow you to effectively distribute heat over the entire usable area as evenly as possible.
Obviously, the most suitable places to install heat sources in the case of heat pumps are outside walls and upper floors under a flat roof or cold attic. However, with a significant size of the building, its central premises remain without active heating, which is not always convenient. This problem can be solved by the correct routing of freon lines or the organization of air heating, the source of heat in which is an atmospheric heat pump.
In the latter case, it is better to place the outdoor unit in a small technical annex, usually located at ground level, which makes it easier to connect to a ground heat exchanger, or on the roof to connect to the solar system field. The indoor unit is located inside the building, connected to the outside through a passage in the enclosing wall. The heated air is transported to consumers through a closed system of air channels:
- a constant air pressure is maintained in the supply circuit, the volume of flow of which for each branch is regulated by channel dampers;
- the inlets of the exhaust ducts are located at points diametrically opposite to the places where the warm supply is installed, through which partially cooled room air is collected and supplied to the outdoor unit, thereby providing a recuperation cycle.
The very possibility of complete control over ventilation implies significant savings. At the same time, the high complexity and cost of air ducts are offset by the relatively low cost of the installation: one unit is always cheaper than several smaller ones with equal total power.
When a heat pump system also includes indoor units with a copper piping system, the cost of communications increases, but the comfort of using the system also increases. On the one hand, it is possible to lay complex wiring of freon lines even with a small thickness of partitions and floors. On the other hand, sometimes a more effective solution is the organization of closed circuits in which the refrigerant circulates, for further parallel connection of indoor units to them – this is what multi-zone systems are designed for..
Duct air conditioners
A separate category of heat pumps, which includes the advantages of air recuperative heating and the efficiency of the inverter circuit, is ducted air conditioners. The concept of hidden placement of indoor units is not new in itself, but heat pumps of this type have become available to a wide range of buyers relatively recently..
The main difference between this configuration is almost complete noiselessness in the presence of indoor units that allow you to set the heating operation mode with high flexibility and accuracy. The only limitation for the installation of channel heat pumps is represented by building structures, which must contain both sufficiently wide cavities for laying channels, and an impressive niche for installing the main unit body. But at the same time, freon lines can be laid in parallel with the air ducts.
The internal block of a duct heat pump performs the function not only of heating the air flow, but also of its distribution to individual consumers, filtration and preparation. A recuperation circuit can also be present, but usually this device is made in the form of an attachment. In addition to ample opportunities for control and configuration, the hidden location of the indoor unit can be simply convenient and will not affect the interior of the room.
Air heat pumps do not yet have to be considered as the main and only source of heating, especially if prolonged temperature drops below -5 …- 10 ° C are possible during the heating period. Installations capable of operating in more extreme temperature conditions exist, but fall into a much higher price category with a longer payback period.
And yet, in the middle temperature range, such devices demonstrate really high efficiency: to replenish heat loss, they need only a quarter of their energy equivalent. With a service life of such equipment over 20-30 years, it manages to pay for itself several times over, so that a timely transition to modern energy-efficient heating systems will help to save in the future, when the price of energy will be much higher than today.