With heat pumps predicted to play a central role in decarbonising heat in new homes as set out in the Government’s Future Home Standard, how can these systems be designed now and, in the years to come, to make the most of their environmental and energy-saving credentials?
Heat pumps are now in the limelight thanks to their recognition in government-backed schemes such as the Green Homes Grant and the Renewable Heat Incentive. With zero emissions at point of use, there is no doubt that they are perfectly placed to help drive down carbon emissions from domestic heating. However, it is essential to design a heating system with ground and air-source heat pumps correctly to enable them to deliver the carbon and energy savings promised. What’s more, it is important to understand how these systems can be taken one step further so that their carbon-reduction potential can be maximised for future residential developments.
Many crucial aspects of heat pump design are related to the low and medium flow temperatures of these systems, such as sizing and controls. Unlike traditional solutions which operate at anywhere between 60 to 85 degrees, any flaws in the design of a heat pump system will result in more noticeable consequences, such as higher electricity bills and lower levels of comfort.
This is why extra attention is needed when calculating pipe sizing and flow rates. Lower flow temperatures and lower temperature differentials for heat pump heating systems mean that more water going through the pipes is needed to ensure sufficient heat transfer. Correctly calculating the system will ensure that the pipework and heat emitters such as radiators will be appropriately sized so that a space is warmed to the desired temperature.
A balancing act
Because water takes the route of least resistance, it wants to flow to the first radiator and not the last in the hydraulic circuit. This is why it is crucial to correctly carry out hydraulic balancing at the commissioning stage so that all heat emitters in a property get the required amount of heat, including the last. Unbalanced systems can lead to higher system return water temperatures, reducing the operational efficiency of the heating system and can also impact on the customer’s comfort.
In essence, hydraulic balancing ensures the flow of water is balanced across all radiators in the system, so that each one receives the right amount of water and therefore heat. It is the final piece of the puzzle in delivering a well-designed, installed and commissioned heating system.
Stay in control
With a traditional high temperature system, the boiler fires up to heat a building to the required temperature quickly. Heating solutions designed to run with lower flow temperatures need to be on for longer, which is why setting up the controls in the correct way is paramount to enable the system to perform efficiently. We recommend using ‘comfort’ and ‘set back’ temperatures. The former is usually around 20-21oC, the latter for night time or when occupants are out of their home or building, at around 16-17oC. Using controls with load or weather compensation will also ensure that a heating system is only on for long enough to maintain the right temperature. So, if only a small increase in energy is required to meet the set temperature, the heating system will work at a reduced output to use the minimum amount of energy needed.