Thermostatic control of socket outlets for portable heaters. OK or not?

[Mark42]

I'm repurposing an agricultural building as a research workshop, where sometimes reasonably accurate air temperature control will be needed.

I want to keep it simple, flexible, and cheap.

Rather that fit modern and expensive wall-mounted heaters, which have a plethora of complicated eco-warrior controls usually impossible to override, I’m planning to use three 2+kW oil-filled portable radiators, plugged in.

I’d leave them permanently plugged in and switched on, with the internal thermostats fixed at max.

Then thermostatically control the supplies to the dedicated socket outlets, using a more accurate and reliable wall-mounted thermostat, centrally positioned, which energises a three phase contactor in the DB, controlling the three sockets.

(There will also be central switching with a timer control and the ability to select only one or more sockets, but none of that detail is relevant to my question).

Of course the sockets would be labelled something like ‘Thermostatically controlled outlet: heater only’, and I may use non-standard pin or old-skool 15A round pin sockets.

Another advantage would be that as this is a clean-room environment with white PVC walls, there’s the option to put the heaters away in the summer, or at least to keep the walls behind them clean.

I concede that this is an entirely non-standard arrangement, which usually generates abuse on this forum (?) but I can see no electrical reason why it's unacceptable or unsafe.

Opinions?

ps. These heaters are only to provide maintenance heating within a few degrees. The main space heating is from a 30kW blown-air diesel heater which will be used each morning to get the whole structure quickly up to temp. It's too noisy to be used during work.

 

[Pete999]

I'm repurposing an agricultural building as a research workshop, where sometimes reasonably accurate air temperature control will be needed.

I want to keep it simple, flexible, and cheap.

Rather that fit modern and expensive wall-mounted heaters, which have a plethora of complicated eco-warrior controls usually impossible to override, I’m planning to use three 2+kW oil-filled portable radiators, plugged in.

I’d leave them permanently plugged in and switched on, with the internal thermostats fixed at max.

Then thermostatically control the supplies to the dedicated socket outlets, using a more accurate and reliable wall-mounted thermostat, centrally positioned, which energises a three phase contactor in the DB, controlling the three sockets.

(There will also be central switching with a timer control and the ability to select only one or more sockets, but none of that detail is relevant to my question).

Of course the sockets would be labelled something like ‘Thermostatically controlled outlet: heater only’, and I may use non-standard pin or old-skool 15A round pin sockets.

Another advantage would be that as this is a clean-room environment with white PVC walls, there’s the option to put the heaters away in the summer, or at least to keep the walls behind them clean.

I concede that this is an entirely non-standard arrangement, which usually generates abuse on this forum (?) but I can see no electrical reason why it's unacceptable or unsafe.

Opinions?

ps. These heaters are only to provide maintenance heating within a few degrees. The main space heating is from a 30kW blown-air diesel heater which will be used each morning to get the whole structure quickly up to temp. It's too noisy to be used during work.

View attachment 63385 View attachment 63386

If it's a clean room it would be better to us A/C for climate control say 70 deg at an RH of 50%

 

[Mark42]

If it's a clean room it would be better to us A/C for climate control say 70 deg at an RH of 50%

Thanks, and I don't disagree. Want to come round and fit it next weekend? I have a budget of £1K for the climate control so you'd be well covered ?.

Seriously: It's not that kind of clean room. More a clean, room. ie not a crappy barn which my rental clients have been offered before by farmers. These people need an open, uncluttered office-like space in which to test x-ray machines and the like. Something like an aviation workshop, not the local garage with black oily walls.

 

[westward10]

I don't see a problem using a stat to control the sockets.

 

[Mark42]

I don't see a problem using a stat to control the sockets.

Thanks.

Nor do I, but I always like to ask about non-standard ideas in case there's something I haven't though of!

 

[pc1966]

As above, sounds fine to me.

My main concern would be how even you need the temperature to be, and how well a central thermostat can achieve it. If you have air-circulating fans then it should be fairly even, but that might prove a little annoying to anyone in a significant draft.

Connector-wise you also have the option of 16A "commando" sockets and plugs, a big bigger than 15A old-UK style but environmentally tougher, also easier to source than non-standard 13A variants.

You could also hard-wire them to FCU. True you would not be able to remove them easily, but as floor-standing they could still be moved a bit away from the walls for cleaning, etc.

Will this be off a single phase or a three-phase supply? If single phase you are looking at something like a 30A or more contactor

If you want a quieter solution you could use a Solid-State Relay to do the power control, but remember they need decent heatsinking and can never be considered a means of isolation (as if they fail it is likely to be short-circuit). But they are acoustically quiet, and also normally switch on zero-crossing so negligible electrical noise as well.

 

[R-fur]

I agree about the commando sockets being more suitable.
Even if it is a single phase supply I would use a three pole contactor and feed each heater from its own MCB.

 

[Mark42]

My main concern would be how even you need the temperature to be, and how well a central thermostat can achieve it. If you have air-circulating fans then it should be fairly even, but that might prove a little annoying to anyone in a significant draft.

Yes agreed. I did think I may also have a second plug-in thermostat on a flying lead, with a change-over switch. Then a customer who needs an even temp in a certain area for a particular piece of equipment can place the 'stat next to it.

It doesn't have to be massively accurate, just better than what we have now in the other workshop where a noisy diesel heater is on and off all the time and the temp is all over the place.

Connector-wise you also have the option of 16A "commando" sockets and plugs ...

No. Too big and unwieldy, and as they are unshuttered I always use the interlocked type which are even bigger. There will be some 16A sockets in the room anyway, as we have a lot of kit with 16A plugs, so this is a non-starter. Too much chance of someone plugging a charger or welder into a temp-controlled socket then moaning to me that it doesn't work!

Will this be off a single phase or a three-phase supply? If single phase you are looking at something like a 30A or more contactor

3P supply.
3-pole contactor with one heater on each phase. Easy!

If you want a quieter solution you could use a Solid-State Relay ...

Interesting idea, thanks. And something for me to research for use in the house. Not needed here though, a few clicks won't matter.