The heating, ventilation and air-conditioning (HVAC) system of a cottage is shown in figure 4.2. The HVAC system main elements are central sectional air conditioner, air ductwork system, ventilating equipment and fittings as well. The central sectional air conditioner of HVAC system, being a part of the ground-to-air heat pump system, is designed for operation both in a cooling mode in summer and a reversing mode (heat pump mode) in a cold period.
Distribution of the treated and heated air, intended for rooms heating in a cold period of the year, is sketched in the figure. The treated air flow is distributed along the channels of the air ductwork system. The distribution in rooms is performed with the help of the adjusted supply-and-exhaust ventilating equipment.
The central sectional air conditioner of HVAC system is non-autonomous, i.e. the external source of cold and heat is needed for its operation. In this case it is a refrigerant from external aggregate. In addition to cooling and heating, the central air conditioner can ventilate, purify and moisten the air.
To shorten the heat energy consumption, connected with air heating in a cold season, the air recirculation and the heat recuperation (heat recovery) are used in central air conditioners.
The central air conditioner, working with recirculation, is completed with a mixing chamber that enables to supply a variable volume of the outside (fresh) and recirculating air.
The percentage ratio of the given mixture is adjusted with automation settings, and is defined in accordance with sanitary norms and rules of SNiP 31-05-2003 and SNiP 41-01-2003.
A heat recovery unit (recuperative heat exchanger) is to be installed in conditioners with heat recuperation. There is no mixture of outside and recirculating air flows in it, and the heat from the discharged air is transferred to the outside air in a heat exchanger. There are the following types of recuperators:
- cross-flow recuperators (plate-type heat exchangers)
- rotary recuperators (rotary heat exchangers)
- recuperators with intermediate heat-transfer fluids
- chamber recuperators
- heat pipes
In the example given, basic elements of the refrigeration unit (in winter – heat pump mode) are Bitzer 4NE-20.F4Y-40S semi-hermetic reciprocating compressor and shell-and-tube heat exchanger, working in a condenser mode in summer and in a reversing one (evaporator mode) in winter. The pump for heat-transfer fluid/cooling medium, connected to the ground manifold, is also included as a compound of the unit. The unit is to be installed in a separate room or outside. The elements are schematically shown on a diagram in the article “Ground-to-air heat pump”.
The unit of the given type (regarding to rooms air heating) can also be a supplement to main heating system and provide a comfort quality of air mixture in house rooms or in office building spaces. The advantage over the battery heating is that, with the aid of automation system, such parameters as temperature, relative humidity, number of air changes, percentage ratio of the supplied outside air and the recirculating air can be regulated.