Predicting performance from Nu-Heat

The new MCS Microgeneration Installation Standard (MIS 3005) has been released. It requires heat pump systems to be at least 100 per cent sized for a property for 99 per cent of the heating season. It also requires systems to be designed to a target external design temperature of between approximately -1°C and -4°C, depending where the property is located in the UK. This means the heat pump should be able to almost entirely heat the house without electric or other back up, under all but the most extreme conditions

“Many heat pump suppliers quote a Coefficient of Performance (CoP) figure based on an outside temperature of 7°C and a flow temperature of 35°C,” said Nu-Heat’s product development manager, Mark Millett. “This temperature range is potentially misleading. Nu-Heat quotes outputs of its heat pump range based on -3°C outside air temperature and water delivery temperatures anywhere in the range of 40°C – 60°C, depending on heating system type. The CoP is really only useful when viewed as a seasonal average. This is why Nu-Heat runs a performance simulation on each and every quote taking into account domestic hot water production and specific local climate data, as well as correctly assessing the heating system itself to determine its optimum operating temperatures.”

Nu-Heat began development of design software in 2009 to address the very issue of correctly sizing heat pumps through performance simulation. Predictor takes published data from various manufacturers into a common platform, so performance levels of any model of any make can be compared easily. Once heat loss has been assessed for a property (through SAP or Nu-Heat’s Optimiser software), Predictor runs a simulation of performance over an average year, based on local, monthly weather data from the Met Office and taking account of the changing seasons.

Predictor uses the daily temperature cycle for the simulations (represented in steps of 1°C and times of day in steps of 4 hours) meaning that it includes cold nights and warm days (acknowledging the fact that a heat pump has to respond to increases and decreases in temperature).

Predictor also takes account of the timing of domestic hot water (DHW) requirements that can have a major effect on the performance levels of the heat pump.  The software helps to work out what time is best to heat the water, indicates what tariff is best to run the heat pump on and produces comparisons with other fuel options such as gas and oil.

When a heat pump is being integrated with underfloor heating, Predictor is used a second time, once the underfloor heating design is completed to double check that the heat pump chosen is still appropriate.

Predictor’s simulations can also be used to generate the commissioning procedure. This helps to set up the parameters of the heat pump and should also aid economy by facilitating more precise settings.

‘With uncertainty about heat pump performance highlighted by last year’s report from the Energy Savings Trust, and DECC’s reticence to include air source heat pumps in the upcoming RHI tariff list, it is imperative that the industry strives to ensure that heat pumps are sized correctly in order to achieve maximum efficiency,’ added Millett.