SPACE HEATER THERMOSTAT SETTINGS 3

[nightfox1925]

Hi gentlemen. Our purchased switchgear is about to be on site and I would like to inquire what is the appropriate setting for the space heater thermostat since this is something I and my group never set.

respectfully...

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[davidbeach]

Thermostat, we don't need no stinking thermostat. One common choice is just to let the heaters run, that is if you specified 240V heaters and have them connected to a 120V source. Otherwise you need to have the thermostat set high enough that you never, never, ever, have condensation; so, it depends on where you are and what your humidity is like. Perhaps a local HVAC engineer can answer your question, then add 10 or 15 degrees to whatever answer you get.

 

[nightfox1925]

Thanks davidbeach. The switchgear space heater is rated for 250VAC, 50Hz and supplied from a 250VAC 50Hz supply. We are located here in Kuwait wherein the system the plant is utilizing a 250VAC, 50Hz line to neutral supply.

Is the setting of these thermostats supposed to be the responsibility of the switchgear manufacturer? Your comments is highly appreciated.

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[ScottyUK]

It is the responsibility of the switchgear manufacturer only if such a clause was inserted into the contract and you furnished sufficient information about the site atmospheric conditions to allow him to make a reasonable estimate of the dewpoint and thus estimate the required setpoint. Otherwise it's your call. The switchgear manufacturer will only build one of two things: his standard line of products, or a design that you specify.

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[nightfox1925]

Thanks scottyuk, we will coordinate with our HVAC engineer to verify what is his room ambient design temperature and add 10 degrees for the setting.

By the way, davidbeach...I was just wondering (for my knowledge)why in some places, it is not always advisable to provide thermostats in switchgear space heater circuits?

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[davidbeach]

The thermostat is just something else to go wrong. Using low density heating elements, like 240V heaters at 120V, the life of the heating elements is not impacted by having them on, so just leave them on. Using heating elements at their design voltage, you are taking life out of the element all the time it is on, so you wouldn't want it on all the time if not needed.

 

[nightfox1925]

Thanks davidbeach, I think that's the scenario why thermostats are in place in this part of the world. Thank you for all your inputs.

respectfully...

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[waross]

The purpose of the heaters is to avoid condensation. To avoid condensation, the equipment must be kept above the dew point of the ambient atmosphere. All that is required is a few degrees above the ambient temperature. In a cool dry environment, 50F or 60F may be suitable. In a hot, humid location, condensation may form at 80F or 90F or higher.
My experience with anti-condensation heaters in generators in the tropics is to run without thermostats. Often two similar heaters are wired in series to achieve the result suggested by davidbeach. That is to apply 50% voltage to achieve long life and dependability.
The optimum control of anti-condensation heaters would be with a dew-point sensor to keep the temperature above the dew point. I have never seen this type of control used. I would consider the risk of failure too great.
I would arrange the heaters for 50% voltage and leave them on all the time. For greater security, you may consider a current monitor and alarm panel on a seperate power source to warn of heater failure.
respectfully

 

[waross]

A further note on condensation.
The problem is the temperature of the equipment, not the air.
The air must be kept warm enough to keep the temperature of the solid parts above the dew point.
Consider an offline generator in an unheated building with lots of open doorways and ventilation openings. On a cool evening, the iron and copper in the generator may drop to 75F or 70F. The next morning the ambient temperature may be in the mid 90's. If a breeze brings in warm moist air from a nearby wet or damp area, (ocean, lake, swamp, cooling tower, etc.)the internal parts of the machine may well be below the dew point and the result will be condensation on the iron.
A thermostat will respond to the internal air temperature, not the temperature of the iron, copper and insulators. In the morning, after a cool night, there may be enough of a temperature difference between the air and the solid parts to allow condensation to form.
Davidbeach and I would both use heaters at 50% voltage and leave them on at all times.
respectfully

 

[nightfox1925]

Thanks waross, I will take that into consideration once I get hold of these switchgear vendors. I have to consider though either maintaining 250VAC Line to neutral supply with a heater with higher utilization voltage or go for a step-down 120VAC and maintain 250VAC heaters.

Thanks...

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[davidbeach]

As waross mentioned, you can run two 240V heaters at 120V by connecting them in series on a 240V circuit, provided the heaters are of the same wattage. The downside to that approach is that should one heater fail for any reason you lose both.

 

[nightfox1925]

Thanks david, that is a practical approach. Considering I am using a 250VAC Line to Neutral supply...that will be a good approach and I will discuss that with my switchgear manufacturer.

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