Summertime (part 2)

Summer (or the heat is still on – a bit) I’ve got more to say about Air Conditioning (so that will be another blog) but have you set up your heating systems for Summer?  

Ideally, I like to turn the BMS to a setback position where if the temperature drops too low the heating comes back on and the occupants therefore don’t get TOO cold but the heating is off most of the time. However not all systems can do that and you are often contractually obliged to maintain the same minimum temperatures as you do in winter.  

Many energy managers play around with time settings, reducing hours of operation even beyond their normal frugal settings, often turning the heating off during afternoons when the ambient heat levels are already high.  Whatever the case it is likely that most energy managers will need to have some heating enabled across the summer – if only to provide hot water services and tempering of external air in ventilation systems.

Apart from those of us with process demands this means that our boilers are operating at low levels (with consequent low efficiencies perhaps as low as 20%). Additionally all boilers in circuit will have heated water flowing through them which means heat will be being lost from their pipework (yes it is insulated but it still loses heat) and casings (ditto) as well as through Natural convection up their flues.

And most sites have more than one boiler on the same circuit.  We can however take steps to reduce the harm. Larger boilers are often fitted with automatic back end valves which isolate them from water flow when they are not firing (ideally they should allow the heat within the boiler to decay to some degree before operating) and some boilers have dampers which close their flues when not operating (some questions about explosion relief apply there).

However, such devices can be expensive to retrofit (if nothing else they usually require a significant drain down of the system) they do however make substantial claims on the saving potential. A much simpler way to get a similar effect (in the warmer months at least) is to lock the rotation of the boilers (either manually or via BMS) designating one boiler (two if necessary which gives a little security in case of issues with the primary boiler) as the only operational boiler and turning the manual valves on the others off, cutting the water flow through the unused boilers and eliminating their contribution to the heat loss.

And if a cold snap happens, the site staff (properly briefed) can turn the other boiler(s) back on easily. The cost – a little labour (just remember to turn them back on in time for winter –if you really need them all!)  The Upside is that boilers just sitting in circuit but not used can lose 3-5% of their nominal output through their casings and anything up to 30% (too many variables apply to be definitive but that is typical for a lot of conventionally flued boilers) up their flues –that can be a significant number and this simple step could eliminate most if not all of that loss over the Summer.

Add to that short-cycling protection that I mention in “Black Boxes II” and you could be getting somewhere. (Ideally if you can turn your boilers off completely and use direct water heaters ….)

Read Summertime (part 1) here.