Variable Speed Blowers

[hands]

I asked this question in the Residential Forum but didn't get a very good response, so I hope some of you guys can help me. I'm going to install a 3 ton Heat Pump and AHU system in my own house soon. I'm going to get a Carrier/Bryant/Payne system and was thinking of getting a variable speed AHU. I work on Commercial equipment and don't see a lot of Residential units, so I need your advice. Do the variable speed blowers work good or should I go with a 2 speed blower. My Service Manager told me that a lot of guys are having problems with the variable speed units and parts are much higher. He said that if the duct work is not sized just right, the blower doesn't know what speed to run at. Thanks for any advice you can give me.

[btuhack]

My take, If you don't intend to run the fan continiously or for extended periods, there won't be a financial advantage for the ecm. The eventual motor replacement will be 3-4 times the cost of a psc and may or may not be on the shelf.

[Ed Janowiak]

You either misunderstood whet your service mangers said or he doesnt understand the constant CFM ECM technology. They are a superior product compaired to the older PSC motors.

What kind of external static pressure is your current system running at?

[hvac69]

I haven't worked residential in years and I was tossing the same idea around when I replaced my home unit. I ended up going with a Carrier gas furnace with a variable speed blower and two stage furnace. The energy savings were there, not exactly sure how much, but the comfort level was much greater and well worth the added cost. Had areas of the house that would have a large temperature difference and now they are in line with everywhere else.

[hands]

You either misunderstood whet your service mangers said or he doesnt understand the constant CFM ECM technology. They are a superior product compaired to the older PSC motors.

What kind of external static pressure is your current system running at?

I don't have A/C at this time. My house has electric baseboard heat. It's a Tri-level house and has two attics and the lower and main levels have concrete slab floors. It's going to be a hard install with a lot of duct.
So how does the ECM technology work? Is it true that you can't use just any t-stat for the ECM to work?

[hands]

I haven't worked residential in years and I was tossing the same idea around when I replaced my home unit. I ended up going with a Carrier gas furnace with a variable speed blower and two stage furnace. The energy savings were there, not exactly sure how much, but the comfort level was much greater and well worth the added cost. Had areas of the house that would have a large temperature difference and now they are in line with everywhere else.

Did you have to use the infinity thermostat for the blower to work right?

[hvac69]

Standard two stage thermostat. I dont control humidity.

[pringlel]

If the tax rebate thing is still going on, I am not sure you can get a heat pump or A/c unit with a high enough seer rating in an unit with a Non Ecm motor. Heat pump i believe is 15 and a/c !6. I put in my house a 15 seer heat pump payne I know you didnt ask about the rebate but it may be a consideration it may greatly offset some cost of the unit.

[Ed Janowiak]

I don't have A/C at this time. My house has electric baseboard heat. It's a Tri-level house and has two attics and the lower and main levels have concrete slab floors. It's going to be a hard install with a lot of duct.
So how does the ECM technology work? Is it true that you can't use just any t-stat for the ECM to work?

Variable speed is a misleading term.

Constant CFM would be more appropriate for the premium ECM motor most people call variable speed as it will maintain a constant airflow IE: 1000 or 1200 CFM etc. When set for that airflow as long as its running against a reasonable static pressure.

It is not true that the ECM motors either constant CFM or constant torque models need a special thermostat to operate them.

[cleancondenser]

I think it is over kill and may harm your compressor

For cooling and heating with a heat pump you still need
that minimum C.F.M. of 1,200 400*3tons
Run the fan too slow and you will slug liquid
What will you base the VFD speed on?

Static pressure? Do you have V.A.V.'s in your house?
Is the A coil on top of a forced air gas furnace?
If it IS , I would still say go with a two speed motor.
V.F.D.'s need an analog signal to vary their speed
You would need a special control with a 0 to 10 Volt D.C. Output
On a unit that small I would go conventional
Besides these 1/2 H.P. V.F.D.'s are not cheap

[Ed Janowiak]

I think it is over kill and may harm your compressor

For cooling and heating with a heat pump you still need
that minimum C.F.M. of 1,200 400*3tons
Run the fan too slow and you will slug liquid
What will you base the VFD speed on?

Static pressure? Do you have V.A.V.'s in your house?
Is the A coil on top of a forced air gas furnace?
If it IS , I would still say go with a two speed motor.
V.F.D.'s need an analog signal to vary their speed
You would need a special control with a 0 to 10 Volt D.C. Output
On a unit that small I would go conventional
Besides these 1/2 H.P. V.F.D.'s are not cheap

Are you the service manger?

It's obvious you don't understand the ECM technology, there is no need for a special thermostat or anything else that has to do with a VFD on a system with a ECM constant CFM motor.

The system with the ECM motor just needs to be set up properly and operate at a reasonable static pressure.

There are systems that require a proprietary thermostat, but those thermostats control the boards in the furnace or air handler then the boards control the blowers, no direct specific thermostat to control the blower.

OP

Ball park you are looking at a 300+/- premium for a system with ECM constant airflow technology, you'll get that back a few times over the life of the unit.

I have installed many over the years going back to the original ICM 1.0 motors all the way through the 2.0 and 2.3 models. And have 2 of the 2.3 motors on systems in my own home.

I recommend them and find very few people that understand the technology who are proponents
of their use, but there are a few who aren't fans (pun intended).

[dunkman]

I think it is over kill and may harm your compressor

For cooling and heating with a heat pump you still need
that minimum C.F.M. of 1,200 400*3tons
Run the fan too slow and you will slug liquid
What will you base the VFD speed on?

Static pressure? Do you have V.A.V.'s in your house?
Is the A coil on top of a forced air gas furnace?
If it IS , I would still say go with a two speed motor.
V.F.D.'s need an analog signal to vary their speed
You would need a special control with a 0 to 10 Volt D.C. Output
On a unit that small I would go conventional
Besides these 1/2 H.P. V.F.D.'s are not cheap

Whoa, you don't see much residential do you.

[dunkman]

I asked this question in the Residential Forum but didn't get a very good response, so I hope some of you guys can help me. I'm going to install a 3 ton Heat Pump and AHU system in my own house soon. I'm going to get a Carrier/Bryant/Payne system and was thinking of getting a variable speed AHU. I work on Commercial equipment and don't see a lot of Residential units, so I need your advice. Do the variable speed blowers work good or should I go with a 2 speed blower. My Service Manager told me that a lot of guys are having problems with the variable speed units and parts are much higher. He said that if the duct work is not sized just right, the blower doesn't know what speed to run at. Thanks for any advice you can give me.

Most ECMs can handle close to .9" static (on the absolute high end) But if you are under .5 it'll purr like a kitten. We probably install 50/50 variable speed 2 stage units, verses single stage PSC blown furnaces. The motors themselves hardly ever go bad. Most the time it's the module on the end of the motor that goes, if you have any problems at all. I am going to put an ecm in my house next time, but it depends on what you're comfortable with. Get the extended warranty, because the parts are more money.