Hi,

Anyone feelings on massiveness in radiator heating systems. Following on from the discussions on high or low mass in construction and the debate between UFH and radiators (assuming you need these of course).

I was thinking what are the differences between low water content Steel or Alu radiators and the more volumous cast iron or steel column radiators. The bigger the water content the longer to run upto temp, but when the room stat/TRV/timers switch off the water contained within the unit has more heat to dissipate to the room. Greater thermal inertia.

I was trying to see if one or the other was more or less suited to a relatively well insulated situation as compared to not well insulated Victorian pile, but couldn’t decide whether fast heat up was more or less desirable in either situation, or if the faster cool down was more of a problem in either.

In the colder situation fast warm up is good, but as heat losses are higher the cool down will be quick too. So I thought higher mass, but you’d be colder waiting for the warm up. It’s basically the UFH argument again I suppose.

Any thoughts – just interested.

Cheers Mike up North

Hi,
I agree the problem with short cycling, particularly in an oil boiler which are of fixed output. The flue fan will also energize a number of seconds before firing so as to evacuate the fire box of previous exhaust gas, so it will cool a bit there as well. Most boilers have a pump overrun where any residual temperature is dissipated by the pump coming on for a number of minutes after the burner has switched off. They sometimes spring into life quite a long time later. On this basis a higher water volume with a smallish boiler working at near capacity for longer would appear better at avoiding the sudden temp rises a small volume would have created and hence the cycling.

I’m looking into all sorts of ways of maximizing the efficiency. One way is to use a thermal store exactly as per with the wood/biomass boilers and run the CH circuits from that. This gives you control over the firing cycle time by juggling volume and temps. Also I’m attempting to deplete the store to just below dew point and then boost it in a single all condensing pass – that’s hopefully going to be your supa dupa system. Ideally little or no heating would be required but as usual working in the real world with what we have in front of us.

I’ve noticed the higher volume steel column radiators are surprisingly warm for quite a long time as compared to the regular pressed steel panel radiators.

Cheers, M

I agree your comment on oversize this is usually to get large quantities of domestic hot water faster to supply even more showers. It is difficult to get any sort of boiler in the small sizes. I notice that some of the pellet boilers are now advertised as being for low energy homes and are rated in the 5-10kw range.

I’d struggle to name someone I knew that had gas, none of that round where I live, so it’s always oil or solid fuel.

My design for a CH thermal store would have a mixer on the CH supply, with a very simple weather compensator – tweak it up and down a bit if it colder, also borrowing from the wood systems a similar mixer to control the boiler return temp to just below the dew point. The problem with oil is that the flue dew point is quite low 47deg after that it just a question of getting the maximum store temp up high enough with minimum effort.

Cheers again