Two questions

[Geoman]

I have an office that needs cooling in low outside temperatures. This is a Trane residential heat pump.

Need to cycle the fan for low ambient winter conditions.

What product is the best fan cycling unit for a heat pump? I'm getting the wiring sheets tonight and will have to figure a way to only have it cycle the fan when its on AC.

Some time back many listed a better product than the typical relabeled trane fan cycling. Can you share that again please?

Thanks Rich

[B-Hate-Me]

It sounds almost like you need some sort of an economizer.

You know, suck in some of that free cold air that's just hanging around.

Would an air to air heat X be to expensive?

B

[Geoman]

Yes, I thought of this option as well, but humidity etc is a big concern with this unit in a doctors office. Also, I have to do it on the cheap so if one is cheaper than the other that is the way I have to go on this one. Electric bills aren't a concern on this job, just up front costs.

[gofish]

Rich, I do this all the time using a Johnson Controls P70AA-118C ($54.00 from Johnstones) and a $10 2P2T relay. Trane heat pumps energize on O. Energize the relay in cooling mode and run the condenser fan lead thru the NO contacts, and then to the head pressure control. For heating, parallel the condenser fan circuit thru the NC contacts and downstream of the pressure control.

I'll cycle the head between 170-175 to 235-240.

I tried one of those ICM controls once, once was all I needed. Never again.

Now here's a tip from Mike: when you install the pressure tap on the shrader port, loosen the shrader core a little bit. This will allow the pressure control to continue to sense pressure, even if the shrader depressor fails on the swivel-T. (been there, done that) :-)

[Geoman]

Hi Fish

With the fan cycling like that how long do they last? Our winters go below zero and on some days I see fans overheat because of the excessive cycling. That's why I was thinking of a head pressure control that adjusts the speed rather than turn the motor on and off.

But, experience is everything so I must ask, what problems with the ICM did you have? Aren't they temperature verses pressure sensing? Also, you haven't seen problems with just using a pressure switch overheating the motor due to cycling?

Trying to learn here, I've never had to do this to a heat pump before and wish I didn't have too now.

Rich

[gofish]

Rich, my ambients are a lot different than yours, once & awile we'll get to 30°. As for motors, I've only had to replace one, on a 3 ton rheem. I'm not a motor expert (where's Jake when you need him?), but I would think motor overheating would occur quicker in a motor that wasnt turning full rpm vs one that cycles on and off. As part of your install, put in a Baldor ball bearing CF motor and be done with it. :-)

At 0° ambient, would the CF even come on?

To be fair, the biggest issues I had with the ICM was my application was on a 460/3 2 stage HP. The ICM device was single phase, which meant I had to switch to a single phase

3/4 hp CF motor. It seemed to have a slower response time sensing temperature than a control thats designed to sense pressure. I had one situation where a 7.5 ton hp was freezing up (evap coil) in the middle of the summer, out door ambient of 85°. No outside air, and a return air temp of 65°. Pressure kit solved the problem and they can keep their fricking computer room any temp they want now.

I've got the P70AA-118C on pkg HP's from 2.5 ton thru 15 ton. Most all my applications are 3 phase, so i go with the pressure control, it works for me.

[Jake]

How speed control affects motors depends a lot on how it's done and proper application.

Frequency "chopping" is commonly used as a cheap substitute for full variable frequency, because it will slow motors from line frequency but not speed them up. They also usually cannot add torque at lower speeds, but can be used well in free-air fans or

[Geoman]

The starting in-rush is what I was referring too, Jake.

To Fish and others: The ICM is probably a 'chop' type then, correct? Does it read line temp or does one have to tap into the refrigerant?

Thanks

Rich

[ReRe]

"Geoman" wrote in message news: [e-mail]...

"Jake" wrote in message news:JyKYd.62287$Ze3.53325@attbi_s51...

The starting in-rush is what I was referring too, Jake.

To Fish and others: The ICM is probably a 'chop' type then, correct? Does it read line temp or does one have to tap into the refrigerant?

Thanks

Rich

This is ReRe

I have a whole box of the Hoffmans that I'll sell you. The things would work great if not on a water chiller system. It does allow the head to drop a little too low for the chiller, but would work fine for an ac application. Has a jumper for HP or C only as well as a couple ranges for the variable fan speed, desired LL temp and sleeve or ball bearing fan motor bearings. We have been using the P-70AA-118C for years without much ado. We just wanted to be able to vary the fan speed as opposed to on / off. The Hoffman allowed the head to come up to 285 or so before it engaged the fan (note: we normally cycle or head between 275 -225) This allowed the probe on the LL to sense a warmer temp. (we shoot for 90 for R22) once the LL was warmed up (30 seconds or so) the fan speed would vary to maintain this temp regardless of the pressure. Most important part was phasing. You can order the control with or without an integrated transformer. I recommend going with the transformer... no need to phase it then. For those of you getting ready to ask about the phasing of a single phase condenser... what I mean is that the 2 poles for the control input power to the control must be phased in accordance to the output poles to the fan motor. If you get the controller with the transformer installed, you will have the correct phasing as you tap your power from the load side of the contactor as opposed to tapping your input t-stat wire for the 24 vac which may vary in phase.

BTW, Hoffman makes the Bayloam Kits for Trane for anyone who didn't know.

ReRe