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CORRECTLY SIZING A HEAT PUMP by Neil Hope, head of installer development at NIBE Energy Systems

re you a heating installer looking to delve into the world of heat pumps? Perhaps you’ve already read a thing or two about the low carbon technology being

complicated to design. Heat pumps do need to be designed correctly to perform as they should, but this doesn’t make them complicated. It simply means that they require attention to detail. This is considered best practice across all heating systems. But if you’re new to the world of heat pumps, you have probably need to know what aspects of heat pump design are most critical and why. The key is accurately sizing the heat pump to ensure the systems work as they are designed to. It’s especially important to maximise the energy performance potential of heat pumps, given that an efficient system can deliver higher carbon emissions savings and lower energy demand.

Traditional materials and the risk of theft


ith the value of raw materials regularly increasing, REHAU is urging M&E specifiers and contractors to consider traditional pipework alternatives in order to reduce risk of theft.

This warning comes from polymer specialist, REHAU, as it prepares to

unveil a major new piece of research highlighting copper theft as a significant problem among M&E professionals. Out of 500 architects, M&E specifiers and contractors, 83% of respondents stated they have experienced copper theft at some point. Steve Richmond, head of marketing & technical for building solutions at

REHAU explained: “We have recently seen a 10-year high on some raw material prices, which of course increases its appeal to thieves. This not only has cost implications for construction sites full of new materials, but also causes potential project delays though insurance claims and police reports.” The report also found that fluctuating commodity prices for metal pipes

impact willingness to specify certain products – 29% big influence, 56% fair influence, 10% not much, 3% no influence. The detailed insights will form a series of reports focusing on different building types over 2021. Despite these facts, metal remains a commonly used material for heating and

plumbing pipework. Steve Richmond says this is predominantly down to being the more familiar option to contractors for many years. However, he states that innovations in polymer and jointing technology are creating a major shift regarding the materials used for heating and plumbing pipes. Mr Richmond continued: “While it is easy to list out the benefits of polymer

over metal, this is a debate that has long been dividing the building services industry. Granted both materials have their uses, but in the context of wider building issues the advantages for polymer are clear-cut. Polymers, such as PE-Xa, fluctuate less on price and are not targeted for theft so are a lower risk for contractors.”

Select as closely as possible to the design demands This is a crucial part of the process and there is only a small margin for error. If the heat pump is too big for the house, it will frequently short cycle and put unnecessary strain on the system; if it is too small, the heat pump will not heat the property sufficiently on its own and may need to rely on a backup heater to meet demand. Accurately sizing the heat pump will ensure that the system performs as cost effectively and as efficiently as possible. Factors to consider when accurately sizing a heat pump Heat pump sizes range from around 4kW to 16kW on a typical domestic, single phase electricity supply, with the larger systems typically required in larger homes, although other factors such as the level of insulation, size of heating emitters, seasonal outdoor temperatures and hot water requirements also come into play. Air source heat pump outputs are usually quoted at industry standard temperatures of 7˚C/35˚C, which means that if the air temperature is 7˚C, and the indoor flow temperature is 35˚C, a 10kW heat pump will deliver 10kW of heat. It is important to check, using the manufacturer’s data, that the heat pump will deliver the required output at design conditions, which in the UK range between an outdoor temperature of 0˚C and -5˚C. Heating emitters must be selected to suit the building’s needs Heat emitters, such as radiators may need to be upgraded so that they are appropriately sized and positioned within the property to work with lower flow temperatures. Heat emitters with larger surface areas are great partners for heat pumps. Underfloor heating, for example, also complements the system brilliantly, and radiators can also be upgraded so that they are large enough to deliver the same heat output. A simple way to see how a heating system that is currently connected to a gas or oil boiler would perform with a heat pump is to reduce the flow temperature to 55˚C. This lower temperature means the system is more efficient and affordable to run.

Full heat loss calculations are necessary with all heat pump installations Heat loss calculations for the final design and selection purposes of heat pumps should be conducted on an elemental basis, meaning that the heat loss of walls, roof, windows and floor, for example, should each be calculated and aggregated together. Full room-by-room calculations are essential to ensure that the amount of space that needs heating is accurately measured, while considering the building’s materials and their abilities to reduce heat loss. It’s also important that all the building fabric ‘U’ values are assessed to provide an accurate understanding of the rate at which they conduct heat. Our training course, NIBE Pro offers a streamlined training route for anyone looking to add new skills to their belt and become an MCS Certified Installer.

April 2021


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