Halogen Lamp heating system, diversity?

[timhoward]

I'm in the middle of preparing a quote for installing 12 x 3Kw and 4 x 2Kw halogen heaters in a church.
The system design was provided by a specialist company.

This sort of thing:

The system is specified to be split into five zones to be turned on depending on occupancy. Unless the church is packed it's likely only 3 zones will be in use. I'm trying to work out what degree of diversity I can reasonably apply to the total possible load of 44Kw.
I'm currently erring on very little as it seems possible to fire all up 5 zones at once. I'm not yet clear on whether they are thermostatically controlled.

Which leads onto the next topic. I turned everything on (lighting, organ blower, under pew bar-heating which they are retaining, water heaters etc) and measured 45 amps max demand.
The existing supply is a little 'curious'. At present the supplier fuse is unknown but likely 60A and only one phase is connected and metered on the customer side.
There's:
- two phases coming in using newer tails (only one in use)
-a phase coming in using an older cable (not in use)
-the neutral using another older cable.
-One of the fuses in the newer head is linked to another one.
It feels as though something prompted an upgrade but it's curious the Neutral is still an old cable.
I've confirmed all 3 phases are present with 400v between them all.

What I intend to do, unless wisdom from you fine bunch tell me I'm being silly, is ask them to apply for a supply upgrade to the (worst case) 55KVA and seeing what the DNO make of the current setup.

My hunch is that this project will need a 3x100A supply and if phases are carefully balanced that leads to max demand of 80 amps per phase.
Am I over-estimating max demand? The under pew heating is a constant load with just an over-heat safety stat on each unit.

 

[nicebutdim]

Can't see thermostatic control helping much when these are being used to heat a large space. I'd imagine they'll run flat out for quite some time.

 

[Mikegh]

I'm thinking you can't apply any diversity to the zones as church can reasonably be packed

The heaters themselves. I'm assuming they're full-on radiant heaters and no diversity there either?

 

[brianmoooore]

You have to calculate for mid winter funerals, not the congregation of three or four there every week. Weddings as well, but these are normally in the warmer months.
As Mikegh says above, not much scope for diversity.

 

[Mikegh]

The others shouldn't be too hard to calculate ?
Presumably there's next to no diversity allowable on the total lighting load and nothing on the Pew heating?

There'll be diversity on the water heating anyhow presumably

 

[timhoward]

Thanks everyone for clarifying my thinking. It seems clear that the supply needs to be capable of firing up the whole lot and it all staying on for some time.
The new system is 191 amps, so that alone balanced across phases exceeds the total that the head claims to be able to deliver, even if the new head was 3 different phases.
So we'll get off an upgrade form and see what happens.

I'm presuming that the energy provider will also separately need to be asked afterwards to provide a 3 phase connection and metering to the upgraded 3 phase supply. I haven't handled a single to 3 phase upgrade before so this is all a bit new to me.

Slightly academic but I can't help wondering what would have happened had the max demand fallen comfortably within 180 amps.
Would the energy provider have just happily connected a 3 phase meter even though the new head is only 2 phases, without DNO involvement at all?!

 

[Simon47]

I'd agree - no diversity. Even if thermostatically controlled, cold church, switch on, everything comes on together and stsys on for some time. Personally I hate sitting under a grill, but that's what many places install - we also had that recommended some time ago and I was "not in favour" (and that was before noting we only have a 60A supply).

 

[Mikegh]

I'm assuming they don't have thermostatic control ?

Would be of little value and a distraction , the heaters cycling on/off

There's probably half-full heat control on the units ? which is of little value also

Half- full heat control would be some use if you could control it centrally based on ambient temperature. Wouldn't change diversity though.

 

[nicebutdim]

This whole plan is typical of a church committee. Set a load of people down with a sum total of zero experience between them and let the best salesman win.

In 20 years they'll decide the system is unsuitable and eventually replace it with something even less suitable.

 

[Simon47]

Have you been spying on our meetings !