Slowing down blower on heat pump?

[hockeyoligist2]

I know this is a HVAC question, but Google didn't give me any results. Our lab has a heat pump and the ladies are complaining about the cold draft when the heat is on. The boss lady over the lab found a website that said if you slow down the fan speed on the blower and turn the fan on continuously it will be more comfortable and use less power. She said it would also help with dust problems, which they have.

I opened it up and it has a four speed fan motor, 3/4 HP. I told her that I could change the speed. But I also told her I'm not an HVAC man and didn't know if it would damage the heat pump and/or increase heating costs. She said "make it happen". I stepped it down one speed at a time and they decided on the lowest speed. It has been running for 3 hours now, the ladies love it and it does feel more comfortable.

Any HVAC/Electricians here?

 

[mike7330]

I'm not a hvac man too. but one thing to watch out for during A/c time is the the coil doesn't freeze up. I know you need to have enough air flow over coil in the cooling season

 

[qcroanoke]

I know this is a HVAC question, but Google didn't give me any results. Our lab has a heat pump and the ladies are complaining about the cold draft when the heat is on. The boss lady over the lab found a website that said if you slow down the fan speed on the blower and turn the fan on continuously it will be more comfortable and use less power. She said it would also help with dust problems, which they have.

I opened it up and it has a four speed fan motor, 3/4 HP. I told her that I could change the speed. But I also told her I'm not an HVAC man and didn't know if it would damage the heat pump and/or increase heating costs. She said "make it happen". I stepped it down one speed at a time and they decided on the lowest speed. It has been running for 3 hours now, the ladies love it and it does feel more comfortable.

Any HVAC/Electricians here?

I would wonder if you have enough air flow over your emergency heat backup strips.
(Assuming that your backup is resistance heat.)

 

[ronaldrc]

Don't forget on heat pump mode your evaporator becomes your condenser.

It might raise your head pressure on a warm day on heat enough to open the HPLS
limit.

I would get the manufactors OK first.

 

[hockeyoligist2]

I would wonder if you have enough air flow over your emergency heat backup strips.
(Assuming that your backup is resistance heat.)

Yes, it does have backup resistance heat, that is one of my concerns. It has gone in to backup several times this morning.

 

[hockeyoligist2]

I just got off of the phone with our local HVAC Company. They wouldn't answer any questions. They said they would send out a service guy to evaluate the situation, minimum $150 service call. The boss lady said she doesn't have it in her budget....... At least she signed off on it, I don't want to get blamed for it!

 

[SG-1]

You might try calling the manufacturer & see if they will tell you anything.

 

[hockeyoligist2]

Tried calling the manufacturer, they gave me the phone # of the local HVAC rep.

 

[hockeyoligist2]

Finally, I got a call back from another local HVAC guy, Not the one the manufacturer recommended, he was very helpful! His name and company is in my phone book now. Straight talkers get my attention, so he will get my business! He said that the heat strips need to be on medium high fan speed, everything else should be OK. I'll put in a relay in the morning to trigger the fan speed to medium high when the heat strips come on. I'm leaving now to change it to medium high to preserve the heat strips, I'm sure they will be used tonight, lows in the lower 30's. I will get a relay in the morning, it's getting too close to Miller time now! LOL

 

[kwired]

You probably want high speed for cooling, so you want relay for that also. Just make sure relays are arranged so you are not trying to run more than one speed simultaneously - the blower motor will not like that, make it default to high speed if there is a failure of relay(s).

May want to thermostatically control speed depending on how much heat is being moved. When it is cold outside there is not much heat to move, but on a balmy day there is a pretty fair amount of heat that can be moved and if you slow it too much it will decrease efficiency more than it will hurt anything - I think. Not enough air flow means less condensing in the coil - the gas will just recycle through the compressor and start over again with less heat to gain when passing through evaporator. Failure to evaporate is a bigger problem - that results in liquid hitting the compressor and liquid does not compress - which will happen if you don't run it on high speed for cooling.

 

[Jraef]

The problem is, there are way too many variables to do this properly over the phone (or the internet) without running a risk of unintended consequences. That's why they are insisting on sending a guy out. He needs to see and evaluate everything in the system as a whole. All you are doing is messing with one part of it, the fan speed. That could end up costing them a LOT of money when something else gets damaged. You don't want that to come back on you.

The concept she heard about is generally true when you have 3 phase equipment and can use VFDs, and you have a relatively sophisticated Building Management System (BMS) that can measure and determine the correct speed for the motor at any given moment in time. This is NOT for the faint of heart or the inexperienced, you can get into trouble really fast.

I'll give you an example I was involved in years ago. Commercial building owner heard similar stories, decided to "roll his own" by buying cheap VFDs over the internet and having his electricians install them. However when they slowed down the fans for the HVAC system going into the VAV (Variable Air Volume) ducts but not the supply fans that brought air into the building, then there was more air coming in than was going out, so the doors would not close and they lost a LOT of money on heating and cooling costs by pumping the outdoors full of their conditioned air. So they bought VFDs for the supply fans too, but got the speeds wrong so now they were exhausting more air than they brought in and nobody could OPEN the doors because of the negative air pressure! They ended up spending a LOT more money after the fact to have an HVAC contractor come in a balance the system, install sensors and a new BMS that could handle it all (I was then hired by the HVAC contractor to help program the VFDs).

A better approach might be to just get better air diffusers to keep it from actually blowing ON the women. Not an electrical solution though.

 

[kwired]

The problem is, there are way too many variables to do this properly over the phone (or the internet) without running a risk of unintended consequences. That's why they are insisting on sending a guy out. He needs to see and evaluate everything in the system as a whole. All you are doing is messing with one part of it, the fan speed. That could end up costing them a LOT of money when something else gets damaged. You don't want that to come back on you.

The concept she heard about is generally true when you have 3 phase equipment and can use VFDs, and you have a relatively sophisticated Building Management System (BMS) that can measure and determine the correct speed for the motor at any given moment in time. This is NOT for the faint of heart or the inexperienced, you can get into trouble really fast.

Most of the higher SEER residential units do vary speed of blower. They use ECM motors instead of 3 phase VFD. They are usually 2 stage heat pumps with different blower speed programmed for each stage as well as another speed for back up heat.

Like electricians never get calls for advice but caller doesn't want to have anyone come out and look at things,... then it will surely turn into a big expensive job. This is just a chance to do that to someone else - the HVAC guy.

He can still come back in a couple years and ask who did that and why? Now you have destroyed the whole system:happyyes:

 

[ptonsparky]

Older heat pumps were cold. Esp air to air. Typicaly the fan will normaly switch to high speed if cooling or when turned to ON or continuous run.

How cold is it getting down there? I would not think your backup should be coming on if temps are moderate. It may be due for a ck up.

 

[kwired]

Come to think of it, why would they have put in a multispeed motor if speed is not to be changed?

Finding correct speed is another task, but why the multispeed motor otherwise?

 

[suemarkp]

Depends on how restricted the duct work is, on how much strip heat you need, and cooling usually needs to be one step higher than heating. A given fan unit may also work with two different sizes of heat pumps (e.g. 3 and 4 ton), so the CFM would need to vary based on BTU of the system.

My variable speed system also has three settings on the thermostat for air -- max, efficiency, and comfort. Max runs 400 CFM/ton, efficiency is about 375 CFM/ton, and comfort is a bit less than 350 CFM/ton. Comfort is more comfortable because cooling air is less humid (its colder) and heating air is hotter.

 

[kwired]

Depends on how restricted the duct work is, on how much strip heat you need, and cooling usually needs to be one step higher than heating. A given fan unit may also work with two different sizes of heat pumps (e.g. 3 and 4 ton), so the CFM would need to vary based on BTU of the system.

My variable speed system also has three settings on the thermostat for air -- max, efficiency, and comfort. Max runs 400 CFM/ton, efficiency is about 375 CFM/ton, and comfort is a bit less than 350 CFM/ton. Comfort is more comfortable because cooling air is less humid (its colder) and heating air is hotter.

Like I said

..Finding correct speed is another task..

 

[BullsnPyrs]

Running the fan motor continuously is oten used as a fix for poor layout of the HVAC drops and or Tstat Locations. Have you looked at the ducts? Are they insulated? If not what you are doing by circulating air continuously is increasing the number of cycles your system is going through. You are taking warm air out of the space and cooling it by running it through the ductwork until the unit kicks on. Reverse this come summer. By running a very low fan speed you are accelerating the process by allowing more time in the ducts for heat to exchange. You would be better off increasing the insulation on your ducts and cutting down on the amount of air blowing directly on the complaining party. If the vent isn't adjustable, replace it and cut her air flow down to a trickle. Let the heat pump function as designed.

 

[hockeyoligist2]

Thanks for all of the suggestions.

"Like electricians never get calls for advice but caller doesn't want to have anyone come out and look at things,.."

I understand that, but its not my call to make, It is up to the departments boss lady. My hands are tied, if given the choice I would have called the HVAC guy to start with!

Anyone heard of the Fanhandler? She found that online yesterday evening. It sounds like a small VFD with a control thermostat in the duct. $170. Not sure if that includes motor and/or if the motor would need to be changed. I haven't read the literature yet, she printed it out but I've been tied up with other things.

 

[kwired]

Running the fan motor continuously is oten used as a fix for poor layout of the HVAC drops and or Tstat Locations. Have you looked at the ducts? Are they insulated? If not what you are doing by circulating air continuously is increasing the number of cycles your system is going through. You are taking warm air out of the space and cooling it by running it through the ductwork until the unit kicks on. Reverse this come summer. By running a very low fan speed you are accelerating the process by allowing more time in the ducts for heat to exchange. You would be better off increasing the insulation on your ducts and cutting down on the amount of air blowing directly on the complaining party. If the vent isn't adjustable, replace it and cut her air flow down to a trickle. Let the heat pump function as designed.

(Stick to heating for now to simplify terminology) Continuous running of fan can also be seen as a way to keep air circulating so you have more uniform levels of conditioned air. Insulated ducts - yes, good idea. As long as we are not losing heat to the outside it is still in the heated space someplace we are just stirring it around and making more uniform comfort.

 

[hockeyoligist2]

(Stick to heating for now to simplify terminology) Continuous running of fan can also be seen as a way to keep air circulating so you have more uniform levels of conditioned air. Insulated ducts - yes, good idea. As long as we are not losing heat to the outside it is still in the heated space someplace we are just stirring it around and making more uniform comfort.

Yes kwired I agree, it feels warmer and more comfortable, no cold spots, with the fan running on low continuously. The ducts are insulated and inside the heated space, overhead. So I'm thinking that it is helping pull the heat back in to the proper area. The return is floor level.

I put in a relay about an hour ago that will kick it up to medium high when the heat comes on, it should work when the AC comes on also, didn't test it because I didn't want to hear women screaming. I'll deal with that when they need it in a few months.

The ladies are happy, so far. It will also help with another headache.... Breakers tripping all of the time from their little space heaters under their desks! They have actually turned most of them off! "Ms. cold nature" left hers on, she runs hers year round! They don't understand why you can't plug in a bunch of 1500 watt heaters on the same 20 amp circuit!