The ErP directive and multi zone heating system thermostats

cs-11 (for underfloor heating or manifold based wall hung radiator systems)

Explaining the energy savings and performance advantages of the ErP directive are not the purpose of this article. Instead we wanted to explore some of the practical issues in implementing the directive. At installer level decisions about what controls to buy have become increasing difficult, albeit with ErP there is a clear cost benefit in energy saving for the home owner with higher rated thermos

Most of you are aware from press articles, that newly installed components like wall thermostats are now also energy rated, and that they form part of your energy rating for the heating system, alongside items like boilers and heat pumps.

What is less clear is how the installer makes the right choice of thermostat for multiple zoning of your underfloor heating or manifold based wall hung radiator heating system. The class of the thermostat does not necessarily translate easily into the system. The ErP class of the thermostat gives you points, as part of your heating system. The total value of points allows you to calculate what efficiency band your total system will be. This is required to meet the ErP energy labelling directive, where all heating systems below 70kW are classified on this energy efficiency band.

When you are installing a traditional 1 or 2 zone heating system, with a modulating combi-boiler the ErP classes easily apply, but if you are installing a multi zone system, it is much more unclear. In a multi zone system, a Class 1 time and temperature programmable thermostat can be classed as a Class 8 solution, ‘Multi-sensor room temperature control, for use with modulating heaters’. This is according to the current guidelines of BEAMA Underfloor Heating Trade Association. This is based on the premise that a manifold based multi zone heating system, with the correct type of wiring centre, including boiler interlock meets the Class 8 criteria, providing a 5% contribution. It is patently clear that a system with multiple zones, each independently time and temperature controlled is more efficient than a single or two zone system.

Multi zone heating has not been clearly addressed as a separate system, so the bias on controls classification is towards their relationship with the heat source, like a combi boiler. For example, Class 5 modulating controls, generally with an OpenTherm link to the boiler, provide an increase of 3%, as they have a direct impact on the efficiency of the modulating combi boiler (by modulating a boilers outlet flow temperature in line with the internal temperature). However, these are designated around using it in a traditional wall hung radiator system, and not multiple room thermostats using manifolds and wiring centres, providing the property with decent energy efficient zoning controls by area.

You may not be in total charge of reaching the target energy efficiency band. It is worth checking what your responsibility will be towards reaching the correct band, before purchasing the thermostats. If the new components of the system are purchased by you, then you are accountable. And depending on these, the final efficiency labelling may need increasing by the choice of thermostats and how you use them in the system. The higher the class of the thermostats, the more weighting it gives to the final system energy efficiency rating. Each element of the system that qualifies to have an ErP rating needs to be included, and the total values calculated, to arrive at the efficiency rating.