HVAC Querie

[Robert Reed]

I have electric baseboard convection heat thru out my house with individual room thermostats. These thermostats are of the bi-mettallic 'snap action' design, in other words they are inserted directly in the power feed and operate the heaters by a mechanical relay action. Initially, they worked OK in some rooms, while operation of others have deteriorated over the years (these would be the ones that never worked satisfactorily). So I have just completed a design of a new thermostat based on an LM34 sensor. The range of control is 55F to 85F with a built in 2 degree hysterisis. The problem with the originals is that hysterisis is too wide and somewhat unpredictable - hopefully the new design will overcome these problems. Well just as I am about to install it, I got to wondering if maybe the location of the thermostat might be causing some of the problem. At any rate, I will replace existing one in same location and in the meantime post this for any ideas you may have on locations. Thanx

[Bigglez]

I have electric baseboard convection heat thru out my house with individual room thermostats.

That would be an expensive option here, California electric
rates are currently just north of fourteen cents a KW-hr.

I got to wondering if maybe the location of the thermostat might be causing some of the problem. At any rate, I will replace existing one in same location and in the meantime post this for any ideas you may have on locations.

I was told by two different HVAC companies that the
secret to good design is the location of the return
registers (for forced air or AC) and location of the
thermostat. In one case it was for radiant hot water
baseboard heater in my vacation home, so somewhat
similar to your case.

From your diagram it is good that the heater is under
the window, and originally the thermostat was placed
adjacent to the door as accepted practice. It also helps
with the cable run, which has an impact on costs if you're
doing this work for a living.

If your goal is to get uniform heating through the room
I'd suggest placing the thermostat as far as possible from
the heater, in your diagram this would be the lower left.

Radiant heating has a different "personality" to forced
air, the radiant heat is felt by exposed flesh as IR, while
forced air requires transfer by conduction. Forced air
has a much faster response, and as the air is moving it
has to be much hotter at the register to prevent a chill
to humans (which is why the furnace fires before the
blower, to prevent a blast of cold air at start up). I
suspect the anticipator in the thermostat for forced air
has a higher hysteresis.

If you are still in the experimental stages try running
the system open loop and measure the air temp at
the old location and at another one for comparision.

As hot air rises a ceiling fan is a great way to stir the
air and make the room cosy for humans.

[bodgy]

Aah the terminolgy difference between English speaking languages, what is a baseboard heater?

Is it an outlet that is piped under the floor and vents out in the skirting board, or more like a free standing radiator style?

As I typed that I just realised that certainly in Queensland, Australian homes do not have skirting boards as in the UK sense - taken me 14 years to notice that.



Colin

[Bigglez]

what is a baseboard heater?

language translation help

Is it an outlet that is piped under the floor and vents out in the skirting board, or more like a free standing radiator style?

A low profile heat source (either electric or hot water) with
enclosed fins and a louver top. Runs can be added to cover
the entire room perimeter or as discrete units (usually under
windows). Either replaces or is attached to the skirting board
(aka baseboard).