I have a 3 zone office building that uses gas furnaces for the main source of heat and downstream they installed tutco duct heaters in every room as supplemental heat. I keep burning up elements because the airflow is not sufficient by the time it gets to the heater. They just keep cycling on and off with the limit. The blower motor is wired to run all the time on high speed. Any suggestions?
Tutco duct heater
Festis8
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I have a 3 zone office building that uses gas furnaces for the main source of heat and downstream they installed tutco duct heaters in every room as supplemental heat. I keep burning up elements because the airflow is not sufficient by the time it gets to the heater. They just keep cycling on and off with the limit. The blower motor is wired to run all the time on high speed. Any suggestions?
Sorry I guess I should have stated that I have 15yrs of commercial service experience I am new to this forum though. I have been thru the furnace no issues there and its is just the duct heater that cycles on the limit. This is set up that the furnace is set on 70 and each office has it own stat that controls their heater indepently as long as the airflow switch in the heater is closed so I have enough flow to close the airflow switch but not enough to cool the elements temp rise across is 60 degrees before the limit trips. Every heater is doing the same thing I also think it is a design issue but I need come up with a solution I was thinking about putting in lower wattage elements. The current element is 6670 watts 480 volt.
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Is this a correct application for duct heaters? With heated air, from the furnace, being supplied to them? What is the temperature of the air entering the duct heaters? In the commercial world, I never see an entering air temp of more than room temperature, usually less, and sometimes as low as 55F. And even then, with a hiccup, like power failure, I will sometimes have a limit trip. I can only imagine how it would be with an entering air temp from a furnace. Where "normal" operation would have it operating even closer to the limits.
No I do not believe this was designed right, but as the guy now in charge of the maintenance for this school district I am looking for ideas of how I can make this work. My guess is somebody added these duct heaters after the install was done. It is a block building with no insulation in the walls and all of the offices are on the exterior walls. A few of the heaters someone installed inline stats to not allow the duct heater to run when the supply air is above 75 but that didn't seem to help either found bad elements in them to.
ELECTRIC HEAT
For an electric furnace the airflow measurement procedure is the same. Allow the appliance to operate until the temperature rise stabilizes. Measure the temperature rise again out of the line of sight of the electric heater, along with the incoming volts and current draw in amps to the electric strip heaters. Enter the information into the following formula.
CFM = (Volts x Amps x 3.41) / (1.08 x DT)
http://www.trutechtools.com/Measuring-Airflow-using-the-Temperature-Rise-Method_c_255.html
Highly doubt that heater is sized for entering air temp like that.
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Has this setup ever worked well?
When you said "the blower motor", were you talking about a central blower, like an air handler? Or does this system have VAV boxes, each with its own fan?
When you said "the blower motor", were you talking about a central blower, like an air handler? Or does this system have VAV boxes, each with its own fan?
No I don't think it ever worked very well, I don't know how it could of. It is set up like a standard split system only they added these duct heaters in the branch runs of the ducts going to each office. The only thing that moves air is blower in the furnace.
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and what controls the heaters?
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Tutco technical service can tell you what the maximum air entering temperature for those duct heaters would be.
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It sounds like it's nearing time for the School Board to free up some money for a new system.
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You could think about either adding a small supply duct blower for each Tutco Heater Assembly (thereby helping to overcome the static loss of the main ductwork), or, replace the Tutco Heater with a fan powered electric heat Terminal Box taking return air from the space . Each controlled by its own respective thermostat.
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What the heat rise thru furnace? Is it within specs.
What is tempature of electric heat limit.
Is there something preventing furnace from operating with electric heat at same time? Your furnace maybe tripping your electric limits by itself.
If you have 60 to 80 heat rise thru furnace you supply air is 130 to 150 degree with 70 degree return.
Typically you have 55 degree air entering Electic reheat with temp rise around 50 degrees. So around 105 supply. If your heating 130(with furnace) air to 180(reheat) your way above limit for electric heat.
Worked on fan powered box today with electric reheat limit at 130 degrees.
What is tempature of electric heat limit.
Is there something preventing furnace from operating with electric heat at same time? Your furnace maybe tripping your electric limits by itself.
If you have 60 to 80 heat rise thru furnace you supply air is 130 to 150 degree with 70 degree return.
Typically you have 55 degree air entering Electic reheat with temp rise around 50 degrees. So around 105 supply. If your heating 130(with furnace) air to 180(reheat) your way above limit for electric heat.
Worked on fan powered box today with electric reheat limit at 130 degrees.
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They have them.
It becomes a design question, involving whether or not the pressure switch is intended to decide if there is enough airflow for good operation, or to detect if there is simply, "airflow."
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Are those electric heaters for heating ? What controls the three zones for AC? Are those heaters for reheat for the three zone cooling? I have a customer w/ that setup.
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