Air to water heat pumps
Heat Pumps are an economical way to heat your home, with low carbon emissions. They can offer easy Part L compliance and are viewed favourably in the latest NZEB regulations.
- Lower running costs than a gas or oil boiler
- Lower carbon emissions
- Good solution for Part L Compliance in new buildings
- More expensive to install than a gas or oil boiler
- May not be suitable for use in some older homes
RVR Energy Technology supply both monobloc and split heat pumps from Immergas and Mitsubishi.
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Is a heat pump suited to my house?
In a new build, Heat Pumps are viewed very favourably during a BER assessment. The methodology for the new “NZEB” (Near Zero Energy Buildings) building regulations has seen their positive contribution to a building’s rating increase. As a result, they are a good choice for meeting Part L requirements during the construction of self-build and multi-unit houses.
Heat pumps can work well in older houses providing the insulation levels of the building have already been improved. In some cases, the size of the radiators may need to be increased.
How does a heat pump work?
A heat pump operates using a refrigeration circuit. Heat is taken from the outside air and delivered into the heating water or hot water cylinder. Heat pumps operate using electricity. As a heat pump delivers more energy than it consumes, it is considered a renewable heating technology. An air source or Air to Water Heat Pump is the most commonly found type of heat pump in the market. Other types, such as geothermal heat pumps, take heat from groundwater or other sources, but are less common.
While a quick estimate may be possible, the sizing of a heat pump is generally done based on the results of the DEAP BER assessment software, especially in a new build.
How much energy your building consumes and whether there is a secondary heat source will affect the sizing. In a house, while an existing gas or oil boiler may have a capacity of 24 or 32kW, it is rare to find heat pumps much larger than about 14-16kW of actual capacity on the market, as this is at the upper limit of what a typical single phase electricity supply will allow. This means that even the largest heat pump will have approximately half the capacity of a gas or oil boiler.
More limiting is that the capacity of a heat pump to extract heat from the air falls as the outside temperature drops. This means that heat pumps need to be sized to meet the heat loss in the coldest expected weather. It may be the case that the design heat loss in your house is greater than the possible capacity of a heat pump, in which case you will either need to keep a secondary heat source for the coldest weather, or embark on upgrading the building’s insulation further before installing a heat pump.
What is the difference between Monobloc and Split?
A monobloc heat pump is installed outside. It is largely self-contained and simply requires power and flow and return heating pipes. Heating water flows between the monobloc outdoor unit and inside the house. The heat delivered into the heating water can be used to heat hot water in a cylinder or to heat underfloor or radiators. This type of heat pump is easy to install and does not generally require a refrigeration specialist to be present during commissioning.
A split heat pump contains two parts – an outdoor unit and an indoor unit. These have refrigerant pipes connected between them during installation. The outdoor unit collects heat from the outside air, and heats the refrigerant gas. The indoor unit transfers this heat to the heating water in the building. During commissioning, an “F-gas” registered refrigeration technician needs to come and fill the refrigerant loop before the unit can be put to use.
As a generalisation, there is little to choose between both types of system. Monobloc units are easier to install while split units are marginally more efficient. Split units are more expensive to commission than monobloc units. Split units may be powered down during winter as the refrigerant gas cannot freeze and cause damage in the outdoor unit, while monobloc units either need to be powered up so that they can provide frost protection or have glycol antifreeze added to the heating system water. Monobloc systems are generally more popular in retro-fit applications as they are easier to install.
Does the hot water cylinder need to be replaced?
If retro fitting a heat pump, an existing cylinder may be used, providing the size of the coil in the cylinder is large enough to allow sufficient heat exchange to take place. In many cases the cylinder needs to be replaced as the coil does not have enough capacity for a heat pump based system. Your installer can check this.
A pre-plumbed or pre-packaged cylinder will often be used. These will contain many of the components needed to easily connect and control the heat pump. These may include a pre-connected manifold for the flow and return pipes and distribution to the heating zones, zone valves and three way valve, and controls.
A pre-plumbed cylinder will look like a standard cylinder with some pipes and boxes on the side. A pre-packaged cylinder will have an enclosure and will look like a fridge. Pre-packaged cylinders are more appealing to look at, but pre-plumbed cylinders cost less. Both will be just as effective.
Will radiators work? What about underfloor?
The lower the temperature of the heating water in the system, the higher the efficiency of the heat pump. Running a heat pump at 35C (Underfloor) will be more efficient than running it at 45C (Oversized or fan assisted radiators) which will in turn be more efficient tan trying to run it at 55C (standard radiators). Low temperature operation on underfloor will offer the most efficient operation and the lowest running costs. However operation on rads will still cost less than using a gas or oil boiler. It may not be possible to run the heat pump on standard radiators as they will have been designed to run at 80C and may be too small to emit enough heat when run at 55C.
What about controls?
Heat pumps may be controlled like any other heat source. Thermostats / Programmers or even web enabled controls are possible. Control systems using optimum start and optimum stop may be useful as these predict when to start and stop the heating to hit your target temperatures at the time you specify.
Are there other types of heat pump?
Heat pump water heaters are available which generate hot water using energy from the outside air. These generally consist of a cylinder with a built in heat pump. Fresh air and exhaust air are typically ducted from/to outside. These heat pumps have a much smaller capacity and are dedicated entirely to water heating. They do not provide any contribution to central heating.