Supply requirement for heaters

Surely they mean it's a 72kW gas heater, with the electric supply for the controls and blower?

At full whack a 72kW electric heater would be using ~£20+ a hour, 5 days at 8 hours a day equals around £20k of electric for 6 months of winter use, reduce it a bit for the warmer days, even so, it's going to be £12-15k / yr for one shift of heating.

Hang on. £20/hr x 8 x 5 x 26 = £20,800. Granted the heating could be off for say 4 summer months, and tapering in spring and autumn, but it has to be at least £20k on that basis. Gas would be circa £7k.

If it is a gas-powered heater, that is comparable to mine at home, but the calorifier does not fire continuously: surely there is a thermostat somewhere!

I think that Alan is correct and it should all become clear on the site visit.

It is one of these - All electric and no gas. It's for heating up a large main hall prior to an event or performance. It would only be on for a couple of hours prior to the show etc starting. Idea is to try to get more use of the area during the colder months.

El-Björn UK Ltd - Commercial Heaters - TF72 EBC

El-Bjorn TF 72EL EBC Electric Fan Heater - 3 Phase

This model can be run at 36KW or 72KW. They also do a 36KW only model.

Don't know about existing arrangements but the site head has been onto National Grid about a new 100A TPN metered supply.

Spoke to National Grid, they don’t seem to hold a lot of information on our setup, but he did say that there is no agreed KVA and that each phase of the existing 3 phase supply would be 100A. That was it.

There is already a 3 phase supply to the building whereby the cable comes in from under the road to an old Fox Barley distribution board (property of DNO?) and from there, various meter tails go off to different meters in the remote meter area and then out to various other DBs.

Am not sure but I think the incoming supply is rated at 300A.

am not confident that these valuses are correct for the KW ratings.

My calculations give 104.3A and 52.2A - so in agreement with yours I think. I also notice that web site suggests a 125A extension lead to be used with the 72kW version - so that stacks up as well.

   - Andy.

I agree with Andy. The instruction manual suggests that a further 4.5 kW are required for the fan. It also states a "rated current" of 110 A. I agree that 35 mm² cable would be required.

The 36 kW model has a rated current of 57 A.

I find it a little odd that the heating capacity is given for a certain floor area when surely, the volume of the space would seem to be more appropriate.

I find it a little odd that the heating capacity is given for a certain floor area when surely, the volume of the space would seem to be more appropriate.

The heating world seems to be full of approximations and rules of thumb (e.g. x sized boiler for a n bedroom house). If you're talking about heating an ideal empty space, then yes, the volume of the air might be about the main factor to consider. But if you were talking about keeping a volume warm, the area of the envelope that contains it (and the thermal resistance of that envelope) would be much more significant. Real world would be some complicated mix of the two approaches (and probably an acceptable warm up time, and weather conditions as well).

I guess most of the time people just want a bit of advise from someone who's done this sort of thing before - e.g. the "big one" is usually OK a for medium size marquee, the "very big one" for anything much larger ... maybe the floor area is just an approximation of that kind of approximation?

   - Andy.

I urge not calculating with too much precision. If the heater is designed 220 volts, and is connected to 250 volt supply, it will draw significantly more current then calculation suggests.

I urge the use of OCPD and cable rated for 125 amps. Also consider that the heater may be replaced with another of a similar NOMINAL rating, but slightly higher actual  loading, within the lifetime of the electrical installation.

In this instance, the heaters seem to be required only for initial heating. Once you get plenty of people in a space, they will generate their own heat.

It occurs to me that the height of a space might be proportional (or thereabouts) to the floor area, so the approximation may be reasonable.