The operation is based on the inclusion of appropriate valves at circuit level, and of course on the control software. The system is equipped with a modulating system on the water exchange source. For this purpose it is possible to use an inverter motor for the pump or a mixing system consisting of valve and three-way and accumulation reservoir. The modulation signal is supplied from the control unit.

The system uses the heat sources available simultaneously. The simultaneous use may be continuous or partial.

Continuous simultaneous operation
In the case of continuous operation, the typical situation is that for which the exchange on the source side occurs through the simultaneous use of multiple sources on which the total capacity of the heat pump is divided. There is virtually no limit to the share of each source, even if it is obvious that a source which accounts for just 5% does not make sense. The standard configuration provides for the simultaneous use of two sources, one of which air and a water (hydrothermal or geothermal). The system is adaptive, as it is self-regulating even if the two sources are not equivalent. Also control regulates itself continuously on the basis of the measurements recorded.

The performance curve of the unit, in this case represented by a balanced situation, 50% water and 50% air, shows the gain compared to a situation fully air.

Partial simultaneous operation
We use for clarity one system constituted by a air exchanger and by a geothermal heat exchanger or hydrothermal. The unit is a machine that normally functions to air, following the climatic represented by the green line of the diagram. On lowering of the external temperature the performance decreases, up to a point where the provided capacity is no longer sufficient to meet the requirement (bivalence point). The control system that equips the COMPOUND Heat Pumps at this point making come into play in a manner proportional to the water heat exchanger. It is right to work in proportion that you must use a modulating system on the water side. With the use of water the performance curve goes back and the performance is always guaranteed.

The possibility of having two different ways on the source side, lets you use the most suitable exchange throughout the seasons, keeping in mind that the total capacity is actually used only in the coldest period. For that you can only use the air exchange during the mid seasons and the water exchange in conjunction with that air in the cold seasons. This situation is particularly advantageous in systems that use as sources of heat groundwater, since it costs less to run the fans of the air exchanger that the hydrothermal circuit pumps.

The system is extremely flexible. In fact, within certain limits it is possible that one of the two sources is entirely inoperative but the system remains in operation, increasing the level of service, and lowering operating costs. To this it is sometimes advisable to slightly oversize the less expensive heat exchanger, typically the air, so as to maximize the redundancy of the system as a whole and increase the level of overall service.
It is important understand that this system allows the use of a smaller heat pump with respect to that necessary in the case of a fully air-sizing. In fact, much of the capacity of a is of this type of heat pump used during the period in which the outside air temperature is more cold. This means not only a larger unit (and therefore more expensive) but also one by bigger air exchanger, with all the inconveniences due to the positioning and the greater mass of treated air. To imagine this, consider that a 100 kW heat pump can easily become 180 kW only because so much power for a few days a year is required. Through the COMPOUND DROP system all this is exceeded, the unit is 100 kW and the difficult period is dealt with by taking advantage of a water heat exchanger.
The air exchanger usually has a capacity equal to that of the heat pump.
The water exchanger can be of lesser capacity, provided that the sum capacity is adequate. Normally it is suitable for a value between 40% and 50%.

Mixed situation.
Difficulties in the realization of geothermal fields equal to the capacity of the heat pump.
EHigh cost for the realization of the complete geothermal field.
High operating costs of the hydrothermal source side
The solution is particularly suitable for harsh climates.
Situations in which you prefer to use a properly sized heat pumps on a seasonal average value, limiting the size and costs.