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Do Your Thermostats Allow ‘Part L’ Boiler Performance?
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| When householders need to replace existing central heating boilers with new ‘Part L’ mandatory condensing types they should rightfully expect improvements of 10-14% in system efficiency. However, depending on what temperature controls are fitted, they could be in for a shock disappointment. |
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The truth is that a condensing boiler can only deliver peak performance while running in the condensing mode. Without this, it performs the same as any conventional boiler. Boiler performance can be affected by associated controls. Many domestic room thermostats with comparatively slow response rates (i.e. some electro-mechanical types) inhibit condensing from occurring for much of the boiler’s operating time. In fact, in-house controlled tests carried out by Danfoss showed that this type of control permitted the condensing mode to cut in only rarely.
Electronic room thermostats seem to offer the solution, particularly those equipped with chrono-proportional control capability.
As opposed to the temperature-event based On/Off cycling of a traditional room thermostat, chrono-proportional control regulates the amount of time for which the boiler fires. In operation, each hour is split into sections (usually 3) and the controller calculates the proportion of these periods for which the boiler needs to fire 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.
Danfoss’ tests indicated that using On/Off electronic room thermostats, in place of electro-mechanical types, can produce reductions of over 2% in both energy cost and carbon emissions. However, the use of chrono-proportional thermostats can push these savings up to 10%.
Consequently, when fitting a replacement boiler, checks should be made to confirm that the installed room temperature controls allow condensing to be achieved for most of the boiler’s operating time. If they do not, then ideal solutions would be to replace them with either a new Danfoss FlatStat or, for even greater savings, a versatile Danfoss Randall TP5000 Si programmable room thermostat. |
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