A reversible monovalent heat pump can provide a highly efficient alternative to a boiler chiller combination when it comes to cooling and heating, says GEA’s Tim Krambrökers
Reversible monovalent heat pumps provide hot or cold water by reversing the cooling cycle inside the heat pump, as required, and by supplying the heating or cooling duty to the building according to demand.
Reversible heat pumps employ a four-way valve to switch as needed between heating and cooling operation.
For example, GEA Heat Exchangers models in its GEA GAH (N/P) 016-064 FD1 series are designed for indoor or outdoor installation under ambient temperatures between -15 deg C and +43 deg C. They provide heating and cooling duty from 16 to 75 kW, depending on the size of the heat pump.
To cover peak demand for heating or cooling duty, it is possible to operate several reversible heat pumps in parallel, in conjunction with a control system that serves all pumps.
The heat pumps serve the heating or cooling requirements by regulating the speed of the compressor, which enables exactly matching the required water supply temperature.
One or two inverter-controlled scroll compressors regulate the actual duty at 25 to 125 per cent of the duty rating.
One benefit is that a smaller buffer tank can suffice, and that it is not necessary to switch the compressor regularly on and off, saving wear.
With a maximum water supply temperature of 40 deg C, a COP from 3.0, and 5 deg C outdoor temperature, cost-effective operation of a reversible heat pump is possible without disadvantages in comparison to conventional systems.
If heating costs are compared between a condensing boiler and a reversible monovalent heat pump, neither of the two systems – at first glance – reveals a cost benefit over the respective alternative.
Gas heating requires approximately. 2.7 times the energy that a heat pump needs.
However, a heat pump operates in heating mode more cost-effectively than a gas boiler once the annual coefficient of performance (COP) exceeds the electricity/gas price ratio.
Cooling duty virtually for free
Calculation of the heating costs for such heat pumps reveals only half the truth when comparing cost effectiveness of the two systems. If the additional benefits of a reversible, monovalent heat pump are also considered – ie the option of providing air conditioning cooling – these heat pumps offer a clear economic advantage over gas-fuelled condensing boilers.
With heat pump systems the cooling investment is free, whereas the operator of a gas-fuelled condensing boiler must pay the additional investment costs for a chiller to meet cooling duty requirements. A reversible monovalent heat pump only costs 15 per cent more than a standard chiller. Here are the advantages of reversible monovalent air-heat pumps over conventional systems:
- Very low investment costs for the cooling duty;
- Requirement of only one unit for heating and cooling;
- Use of only one water network in a building for both heating and cooling needs;
- The same room units for both heating and cooling;
- Elimination of maintenance costs and investments for condensing boilers;
- Elimination, in many cases, of building connections gas meters;
- No need for basement heating rooms or machine rooms for additional gas heating;
- Better floor-to-space ratio in the building as there is no heating room;
- In comparison to oil heating – no oil tank required;
- Choice of installation of heat pumps outside or on the roof, which allows more floorspace for use;`
- Less expense for control systems;
- Highly exact and energy-efficient temperature control.
An air heat pump takes approximately two-thirds of its heat energy from the environment, which represents a regenerative energy source.
If, in future, the share of green electricity increases in the power mains, operation of a heat pump will reduce its CO2 footprint accordingly.
For heating with air heat pumps, consider whether the lowest expected temperatures in winter will lie below the operating limits specified by the manufacturer.
Exact analysis is necessary for considering each potential case of employment of a reversible heat pump.
The type, location, and duration of system operation play just as important a role here as room conditions.
In most cases, a profitability analysis for reversible heat pumps will pay off for applications with alternating heating and cooling duty requirements.
Tim Krambrökers is head of refrigeration / chiller product manager at GEA Air Treatment