New technologies needed
Current mainstream controls are magnificent examples of design and engineering and will continue to do what they were designed for; but we have refined them to the point where their further significant development no longer seems feasible. We must look to new technologies to achieve the additional savings that are now so important.
Many installers seem reluctant to adopt advantageous controls advances and yet only minimal (if any) extra training is required and cost impacts on the user are relatively low. As these changes seem unavoidable, why not act sooner than later.
Effect of condensing boilers
One recent factor in the controls evolution process has been that high-efficiency condensing boilers are now mandatory in new-build and most refurbished private housing.
Regretfully, simply installing a Class A condensing boiler does not automatically achieve the high energy-savings that its SEDBUK rating might suggest. Unless the heating system’s controls are sufficiently responsive to allow the boiler to operate in condensing mode for reasonable periods, any savings are likely to be insignificant. This is especially true when old boilers are being replaced and the existing heating controls are left unchanged.
Room thermostats
Most electro-mechanical, bi-metal room thermostats that were always considered to be low-cost, reliable, functional and easy to use are just not responsive enough to sustain a boiler in condensing mode for any length of time. Obviously, if a condensing boiler is not allowed to condense, it offers little or no advantage over a standard appliance.
The solution is to simply fit a more responsive electronic On/Off thermostat that can make all the difference, and restore the functionality of the boiler.
Programmable room thermostats
We need to go much further than using simple room thermostats controlling at one preset room temperature to achieve the extra savings required.
Central heating systems should provide heat only when it is needed. During most weeks, there are regular periods when houses are unoccupied (shopping, dog walking, visiting, etc.) and others when lower room temperatures are acceptable (e.g. morning housework). A programmable room thermostat enables these low and zero heating periods to be implemented in a way not possible with a single-temperature control.
The electronic sensor and switching action of a programmable room thermostat will ensures a condensing boiler operates to full effect. These flexible controls, having been available for some years, cannot be designated as latest technology but fitting one in a house can make a huge saving on the heating bills.
Chrono-proportional control
What more can we do? Should we also be questioning whether On/Off control is still appropriate? To make the ambitious savings targets now required, should we take a lead from commercial HVAC systems and use modulating control?
The use of chrono-proportional controls domestically can produce a very marked improvement on even the performance of programmable room thermostats.
Chrono-proportional control, instead of reacting to temperature events and going through On/Off cycles, splits each hour into sections (usually 6) and the controller calculates the proportion of these periods for which the boiler fires to maintain desired comfort levels. This modulating control mode provides a closer control band and faster reaction to temperature change, resulting in improved energy savings and better home comfort.
Closely controlled tests carried out by Danfoss Randall showed that using a simple mechanical thermostat meant the energy-saving benefits of a replacement high-efficiency condensing boiler were lost because the boiler rarely operated in condensing mode. Using an on/off electronic room thermostat in the same set-up produced reductions of over 2% in both energy cost and carbon emissions.
However, the use of an electronic thermostat operating in chrono-proportional mode provided closer temperature control plus possible reductions of 10% in both fuel cost and carbon emissions.
Looking ahead
Tomorrow’s central heating controls will need to go beyond the capabilities of traditional mainstream devices. They must be flexible enough to save energy that has previously been wasted. What’s more, they need to be installed now!
Heating installers should not be nervous about looking at all technological advances introduced – chrono-proportional control, optimum start, weather compensation and more – and using these advances to best advantage for their clients.