Emulating thermal mass and lag time

[1Khaleel]

Hello all,

We are testing a heater unit in a climate room.
The climate room, however, is pretty bare and has minimum wall insulation. Therefore, whenever the heater is off, room temperature drops like a stone, which creates an unreal condition, since houses lose heat at a slower rate.

What would be your thoughts on emulating a thermal mass, as in an actual home/house?

We did consider adding furniture to the room, but it is a small room and that would make testing difficult.

I'm thinking of stacking in a few dozen water drums, since water has a high heat storage capacity.

Any suggestions are appreciated.

 

[macmet]

Are you not able to add insulation to the walls so it acts more like a typical house?

 

[gadkinsj]

Put the thermostat inside something with insulation to damp the temperature change locally? IE, put it in one of those 55 gallon drums you mentioned, or something much smaller if possible.

 

[1Khaleel]

macmet, the test room is very restricted by surrounding structure and cannot be modified.

gadkinsj, I should have mentioned that this is a storage heater, so we don't want to influence the room temperature directly. However we know that the current drop is not realistic and that affects the performance of the heater.

 

[IRstuff]

Don't you have control over the "climate room's" temperature settings? Can you ramp the room's temperature to match what you expect?

TTFN
faq731-376

 

[1Khaleel]

IRstuff,
We are trying to quantify the performance of the heater, i.e. how much heating it delivers and how fast it can bring the room temperature to the required comfort level.

The room temperature drop (say overnight, when the heater is off) needs to be a realistic one to simulate that of a house. Currently it is not, which puts more demand on the heater to bring the temperature back up again.

Since we cannot change the climate room structure, we need to introduce a thermal mass that will absorb and retain heat when the heater is on, and slowly release this heat back to the room when the heater is off.

I hope this explains the nature of the problem.

 

[ione]

Water is certainly a good example of a substance which can provide thermal inertia to your room. In general you should look for a material capable to exhibit a high density coupled with a low reflectivity and that behaves as a good, but not excellent, conductor.

You could also look for phase change materials

http://www2.basf.us/corporate/080204_micronal.htm

 

[1Khaleel]

Thanks ione.
I think for now water is the cheaper option.
May be a long term solution would be to use PCMs to give the climate room some artifical, but permenant, thermal mass.

 

[IRstuff]

"Since we cannot change the climate room structure, we need to introduce a thermal mass that will absorb and retain heat when the heater is on, and slowly release this heat back to the room when the heater is off."

Again, if you are running the "climate room" uncontrolled, that's a bad testing concept. If it is controlled, then there should be no reason not to ramp the room temperature to what you want. Seems to me that using another of your heaters set to the minimum allowable room temperature would be adequate, unless you have not fully described your test.

TTFN
faq731-376

 

[1Khaleel]

Thanks everybody for your suggestions.
We are revising the climate room build and how it can be modified to create a more realistic thermal mass.

 

[StoneCold]

It would seem to me that you could look at the enthalpy of the entire system. Create your ideal house and try to determine the enthalpy of ideal house at two temperatures. Then create the lab house with an equivalent heat capacity to mimic the ideal house.
I think that 55 gallon drums concentrates the heat too much in one location to be very accurate. I would think that lots smaller containers of water spread out would be a better simulation of a higher thermal mass.
I would also think that the temperature outside your litle room would have a big impact on the heat load. As well as # of windows and "wind" real or simulated.
This seems more like a simulation problem than a problem where you can build a lab inside. Maybe give away a couple of units to people in Wyoming for a test.


Regards
StoneCold

 

[macmet]

What about insulating the inside of the walls? Seems to me that that would take up less room than barrels of water.

I'm not sure about the cycling involved in your testing, but will you have to heat up the large masses of water each time as well?

 

[1Khaleel]

Thanks everybody for the advice.
It seems that our current room does not meet BS 60531, which is specifically created for testing storage heaters. A new room will be built with dimensions and insulation as per the spec.