EuP ready pump – managing the transition

Nu-Heat now offers a range of energy-efficient pump options that meet the requirements of the Energy Using Products Directive (EuP).

Agreed in 2005, the objective of the EuP is to reduce carbon emissions by reducing the amount of energy used, including in domestic heating and hot water.

Nu-Heat now supplies one of the most advanced energy efficient domestic circulators of its kind on the market today; essentially, a direct replacement for previous models. The reduction in power consumption has been achieved by using the latest permanent magnet motor technology.

It hasn’t been the easiest task for Nu-Heat to adapt our existing products to accommodate the EuP-ready pumps and manage the stock transition, but we managed to do this in good time, although it was further complicated by the additional product innovation that is still going on subsequent to the legislation change.

The change has, however, been positive in terms of system design. Nu-Heat now uses a smaller range of pumps but, without exception, the variable-speed equivalent has a greater capacity (both in terms of head and flow capability) than the old fixed-speed counterpart. Being able to do more whilst using less power has to be advantageous.

There are pumps in just about everything that we sell, and different products require the pumps to be set up differently – for example an underfloor heating pump will be set in constant-pressure mode, whereas the shunt pump on our thermal store still needs to run in fixed-speed mode. Heat pumps, on the other hand, tend to use the pump at maximum capacity (the highest fixed-speed mode) in order to get the closest temperature differential. The range of pumps that we use has the capability to fulfill those needs, and our literature offers installers guidance on what mode is suitable.

Within the business variable speed (EuP-ready pumps) seem to have been with us forever, although Nu-Heat’s Technical Support department now has to explain that service replacement pumps will not be the same as the original item. Overall the new pumps represent a better product for the end user.

Chris Weightman, Nu-Heat’s Senior Development Engineer

Renewable heating with supplementary boiler

In the past there used to be a degree of flexibility regarding heat pump sizing; if the heat pump could not cover all the heat load at low outdoor temperatures then direct electric heating picked up the shortfall. However, with tighter control now in place, we discuss what is meant by a ‘supplementary boiler’ (rather than a back-up boiler) in relation to heat pump systems.

The microgeneration standard, MIS3005, requires heat pumps to be sized to at least 100% for 99% of the heating season for any property, meaning that the heat pump should be able to entirely heat the house without electric or other back up under all but the most extreme conditions. In practice, this translates to systems being designed to a target external design temperature of between -0.2°C and -3.9°C, depending where the property is located in the UK.

Nu-Heat always supplies a heat pump that will achieve the 99% target, unless the size of the heat pump is restricted, in which case a supplementary boiler will be needed. This is a possibility where a larger heat pump using a 3-phase electricity supply is required but the local DNO either does not offer 3-phase or it is prohibitively expensive, for example.

A system that incorporates a heat pump and boiler is termed ‘bivalent’, and there are two possible modes of operation.

Bivalent parallel

Down to a certain outdoor temperature the heat pump will be able to cover the whole load on its own. This temperature is known as the bivalent point. If the temperature drops below this in bivalent parallel mode, the heat pump keeps working but the boiler will work alongside it. This is the mode used by Nu-Heat.

Bivalent alternative

When operating in bivalent alternative mode, below the bivalent point the heat pump switches off and the boiler does everything. This is really only likely for systems that require a higher flow temperature (70°C, for example), in a poorly insulated house.

The heat loss parameter of a property needing a supplementary boiler should be as good as (or better than) where a heat pump is used on its own, usually around 60W/m²; this is because the heat loss parameter is directly related to the flow temperature required. The boiler exists to extend the power coverage of the heat pump, but NOT the temperature range.

Nu-Heat believes that a heat pump should be able to supply at least 50% of the power needed at -3°C (so in a property sized for 24kW, the heat pump will cover 12kW or more at -3°C). This is because the bivalent parallel system works by the blending valve taking water from the heat pump and boiler and mixing them proportionally to get the right temperature output. Just below the bivalent point, the heat pump will do most of the work and the boiler will contribute a little (to make up the difference). Therefore, it is important that the boiler isn’t any bigger than it needs to be, or it will cycle on and off under these conditions, adversely affecting energy efficiency. In theory the boiler will never be required to ‘take over’ the heating system.

With the bivalent parallel theory, and in order to maintain the integrity of the system efficiency, boiler sizing is as important as the sizing of the heat pump. However, the choice of boilers on the market dictates that it may well be 12kW or more, so the model must be a modulating version, which means that it can trickle heat as required rather than give 100% heat supply.

As with other systems, heat pumps give priority to domestic hot water over hot water for heating. Therefore, if the DHW calls, the heat pump will answer, and if the heating suffers, the boiler will pick up the difference.

Whichever fuel source is used for the boiler, energy figures should be provided by the fuel supplier or boiler installer before it is fitted, so the homeowner can base their decision on actual costs.

“If you’re fond of sand dunes and salty air”

Unlike ground source heat pumps that require a plant room and either land for ground loops or the right conditions for boreholes, air source heat pumps require little in the way of space for installation. However, in certain locations there may be particular considerations to ensure that air source heat pumps continue to perform to their optimum levels – for example, air source heat pumps situated on the coast.

A ‘coastal’ installation refers to a property that is located within 4 kilometres of the sea ‒ and as Britain is an island, there are a large number of houses that fall into this category. When Nu-Heat specifies any heat pump, a coastal location will be flagged up by the estimators who always consider the property’s location in order to size the unit – in accordance with MCS. Properties on particularly exposed coastal locations such as a cliff top facing out to sea have a greater heat loss, so an increased ‘exposure’ figure is included in the heat loss calculations. The bonus for heat pumps situated on the coast is that the air temperature is generally warmer and there is less chance of frost.

The main issue for a seaside air source heat pump is that the salt in sea air may corrode the heat exchanger within the heat pump, although the solution to this is fairly straightforward. Every air source heat pump that Nu-Heat specifies for a coastal location is treated with Blygold anti-corrosive coating.

Blygold has traditionally been used to protect HVAC coils, and is ideal for air source heat pumps. The coating provides a long lasting corrosion protection without affecting heat transfer and pressure drop, protecting the surface from premature deterioration. The heat conductive pigmentation in the coating creates a very high chemical resistance at a low layer thickness.

One coating should last for five years and can last longer, depending on actual location. The customer is asked to wash the coating annually with soapy water and inform Blygold that they have done this. If the coating shows sign of wear, Blygold can supply a touch-up kit or there is an option of a refurbishment programme that will ensure performance and longevity, although this is unlikely to be required in most situations.

In coastal locations, as with any other location, an air source heat pump should not be contained it in a tight space, next to a high fence or against the wall of the house, as air may leave the unit and return straight back in the other side, reducing efficiency.

With many remote locations having no access to natural gas, the installation of an air source heat pump is an ideal solution, as long as insulation levels are sufficient. Although all new builds will achieve these levels, older properties are likely to require improvements through the installation of various combinations of loft, door and wall insulation and double glazing.

ASHP heat exchanger, Blygold treated
ASHP heat exchanger, untreated with Blygold