Looking for Differential Thermostat


I will be setting up a small fan to equalize temperature in 2 different places. This is actually in a church to keep the temperature of the organ chamber, close to the temperature of the church itself. The reason is to keep organ pipes in the 2 locations, in tune with each other. I have googled this, however, I only come up with a few fancy electronic units. They would probably work ok. But, I was wondering if anyone knows of a simple unit that is capable of switching 110 to the fan. The fan will be a small, 300 CFM or so unit, using just a few amps. Thanks.
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Art Todesco wrote:

More info, please...how far apart the locations you want/need to use as controls and what is the existing input(s) you have, if any?
Are you proposing to simply moving church air as makeup or some other tempered air source?
Do you have any specification from the organ maker/installer/tuner on the differential required to be maintained? Has the installation been modified -- if so, would seem it would have been their job to make sure of ambient conditions (just a question so maybe you can throw the onus onto somebody else :) ).
Have good friend who does organ tunings and retrofits -- give more detail and if like I'll pass on the question to him and ask for input...where is this located, just in case it might be close? Alternative solution would seem to me to be to simply ensure continuous air circulation through the chamber from the other area, but that makes assumptions about what you're actually moving w/ the fan in your suggested solution.
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Art Todesco wrote:

With a common air supply from the wind chest, all the pipes would tend to have the same temperature after the organ is played for a while. If you can make air flow a lot of pipes at the same time, the backpressure and fan pressure could be low, but maybe that's hard to do, if springs in the chest hold valves closed until solenoids open them.

Running the blower before the organ is used, or whenever the church is occupied (with an occupancy sensor) might use less energy. Heliotrope General makes a 120 V differential thermostat, but the min differential is fairly large, about 5 F.
With a dT (F) temp diff, 300 cfm would move about 300dT Btu/h of heat into the pipes, which might lose heat from their surface at 1.5 Btu/h-F-ft^2 to church air at different temperatures. If one part of the church is 50 F and another is 70 and each contains pipes with 300 ft^2 of surface and each receives 150 cfm of air at say, 70 F, the warmer pipes will be 70 F and the cooler pipes will warm to 55, for a 15 F temp diff. With 60 F supply air, the warmer pipes would become 67.5 and the cooler ones would become 52.5, with a 15 F temp diff that would decrease with more airflow but doesn't depend on the supply air temp. Like this, viewed in a fixed font:
Tc = 50+1125/450 = 52.5 | 1/150 | 1/(1.5x300) 60 ---------www-----------------www--------50 F | | I = (60-50)/(1/150+1/450) = 1125 Btu/h --> | | Th = 70-1125/450 = 67.5 | | | 1/150 | 1/(1.5x300) ----www-----------------www--------70 F
<--- 1125 Btu/h
A clever controller might measure the pipe temps and route 300 cfm of 70 F air to the cooler pipes, raising their temp to 58 while leaving the 70 F pipes unchanged. The chest might also contain a 1500 W space heater.
A small house furnace blower might work. Large organs have blower motors rated in horsepower. You can't open the door to escape from the chest in the First Parish UU Church in Concord MA until you turn off the blower or open a small door slider to lower the air pressure from about 5" of water, which pushes the 2'x5' door closed with about 300 pounds of force.
Nick
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dpb wrote:

the grill where the chamber pipes speak into the church. The church has it's own HVAC system with setbacks, etc. The chamber has no heat, however, when the organ is off, the shades open. My plan it to draw church air through the open shutters into the pipe chamber and deliver it to the room where the blower is installed. This way the church air would be in the chamber and in the blower room. The proposed blower/fan will be installed above the organ blower room, where it would deliver its air. A duct will go to the organ chamber where it will suck causing church air to enter the open shutters, thus bringing the chamber temperature closer to that of the church. This will also keep the intake air temperature in the blower room, closer to that of the church.

have monitored this for the 20 years since installing the instrument. It is worse now because of new setback thermostats in the church. This was something I have always wanted to do, but never had the ambition. Now, it is more important because of the greater temperature differences.

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Art Todesco wrote:

...
I guess the onus _did_ get shifted to the organ contractor... :)
Don't suppose there's any convenient way to get a side duct run from off the sanctuary HVAC system?
Still would seem likely that imply an on/off control and a timer for the routine service schedule would be adequate.
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dpb wrote:

One of the HVAC systems is right next to the organ chamber. I could put a return duct in the chamber. This would tend to suck church air through the open shutters, thus equalizing temps. I am currently waiting for the HVAC guy to come back from vacation, to discuss this with him.
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Art Todesco wrote:

Why do you think you need to control the fan? If you are blowing 'church temperature' air into the chamber, then you will equalize the temperature. Why would you need to turn the fan off?
More detail please.
-tg
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snipped-for-privacy@earthlink.net wrote:

the same temperature, one in each pipe box.
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wrote:

While you're working on this, why not install the fan and whatever means you plan to use to direct the air and keep everything quiet. So your project will be proceeding. Any switch that can control anything electrical can control 110 volts by means of a relay.
Maybe when you are done, you'll be able to just use a simple thermostat in the organ room, and won't mind if the fan runs a bit more than you would have it otherwise. After all, if it runs more now, and when it turns off 5 minutes later than planned, it will start again later than it would have. So you'll break even.
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