Carrier 58MVP Series 140--Blower Specs--Custom Config. - DIY Chatroom

mogmen · 10-30-2009, 10:16 PM

Hello,

I am hopeful that someone can help me out of the problem i worked myself into. I have searched the site to find answers but could not find what i am need. However, i do see that there are many knowledgeable people so i will give it a try.

The specific information i am looking is the max allowable air temperature that the blower motor in my Carrier 58MVP series 140 can operate under. This is why.

I am at the final stages of integrating my wood gasification boiler to my Carrier 58MVP. I am using my wood boiler to heat a 1000 gallon storage tank which is not pressurized. I will be taking the water from the tank and running through a coil (heat exchanger) which is located in my cold air return. I realize that the optimal location for the coil would be on the supply side, but i opted for the return side because it would keep the elevation of the coil below the water level in the storage tank keeping the pipes full of water allowing the circulator to work effectively. With the coil on the supply side would have it above the storage tank level allowing the water from the coil to drain back into the storage tank. I thought about using a check valve but i don't think i have enough head pressure to keep the valve sealed completely. So I am

!

So i called the carrier dealer in my area and he told it was not a good idea. He is probably correct, I will be introducing 180 degree F water into the coil which is only four feet from the blower. I would guess the air temp will be at least 120 F when it hits the blower. I am sure they are not designed to see those temps. But will it handle it?

I have no choice. I need to try to come up with a work around.

Is it possible to shroud the motor and feed it cooler air either from outside the system or from upstream of the coil? Can i replace the motor with one which is suitable for these temperatures?

Any thoughts or idea are welcome.

Thanks for taking the time.

Take care,
Ed

yuri · 10-30-2009, 11:04 PM

The furnace itself is rated for a maximum temp rise and that is on the specs with the model#. It is usually under 70-80 deg F. You will overheat the motor, blow the limit control, stress the heat exchanger and void the furnace warranty and can do lots of other nasty things to the furnace. Sorry, it is not designed for that purpose. Putting it downstream may work. May not work as the fan is rated for .5 to.8 "WC static pressure and you may exceed that. If you have no A/C coil it may work. I and some of the other techs can tell you how to check the static pressure drop. Not easy as it gets complex and you need a differential pressure manometer/magnehelic gauge. You have a ECM variable speed fan motor and they are finicky and require a proper set of ductwork and operating conditions/static pressure or they won't maintain a proper speed and will hunt and get damaged. I would get a seperate airhandler for the job and see if you can twin the ductwork and have them in parallel may be one possibility. Hang in there, some of the other guys may have some better ideas.

beenthere · 10-30-2009, 11:58 PM

You will burn out a very expensive motor.

The water, would not drain back into the tank if the coil was in the supply plenum. Unless you had a leak in either the coil, or the piping.
Or your piping in the tank, didn't have both pipes below the water level in the tank.

Need full model number of furnace to know what blower it has.
However. It will only be about 50% of high cool speed.

mogmen · 10-31-2009, 09:04 AM

Yuri,

Thank you for the reply.

So it looks like need to figure out a way to put it in the supply side. I do have AC coils in the supply plenum. Does it matter if the hot water coil is installed before or after the AC coil? Currently the AC coil sits on top of the furnace. Can i place the hot water coil on top of the furnace and move the AC coil above it? If needed can i place the AC coil in the return?

Thanks agian for the help.

Ed

mogmen · 10-31-2009, 09:15 AM

Beenthere,

Thank you for the reply.

My tank is at atomspheric pressure. it is not completely closed. There are openings on the top of the tank so i place my domestic hot water coil inside the tank. If the hot water coil is above the water level even though both the supply and return are exiting from the bottom of the tank wont gravity let the water in the coil drain back into the tank? I had thought it would.

Thanks again.
Ed

yuri · 10-31-2009, 09:51 AM

You cannot place the A/C coil in the return duct. Moisture off the coil can damage the motor and heat exchanger and the cooling effect on the heat exchanger will cause it to sweat and get damaged. Depending on how tight/restrictive the hot water coil is it may add too much back pressure to the fan motor. This is measured as static pressure. Fortunately the ECM motor may compensate for that as it is designed for that. No way to know for sure until the coil is installed. How about my extra air handler idea? Do you have room for it? Beenthere is correct in that your fan will only run at 1/2 speed on continuous and there is no way to alter that. Won't be able to move much air if the 2 coils are adding too much load. The ECM motor is programmed for a certain maximum load and after that will hunt/not run at a continuous speed. Just want you to be aware of all this before you go ahead and have to rip it out later.

beenthere · 10-31-2009, 12:58 PM

Take a straw, Put one end of it in a glass of water. Then cover the other end with your finger, and lift the straw out of the glass. Doesn't the water stay in the straw.

Coil works the same way, as long as air can't get in, water won't run out.

I have several hydro coils installed like this. No problem.

As Yuri said. A/C coil in the return is problems also. It will also cause moisture to condense in the heat exchanger in the winter. And rot the heat exchanger out from the inside out.

How ever. It won't harm the ECM motor(sorry Yuri).
Air handlers with VS blowers have the coil before the blower motor. So no real problem. Unless it sucks the water off the coil.

beenthere · 10-31-2009, 01:01 PM

You may need to add more return to your system. Usually thats not too hard to do. It will enable the blower to move air easier through the A/C and hydro coil.

Make sure you leave some space between the coils, and between the furnace and the hydro coil. That help to move air better.

mogmen · 10-31-2009, 06:04 PM

OK. It sounds like it is not a total catastophy. I understand exactly what you are saying about the water in the coil. You are right. The guy at the plumbing store encouraged me to put it as low as possible. I wish i had consulted this forum before i modified my return air duct. Education does cost money.

I looked inside the supply plenum and the AC coil currently sits directly on the furnace. I have eight inches until the first penetration. I cannot raise the incoming duct because it is coming under an I beam and is already tight to the bottom flange. I cannot run it above because i will be into the floor joist.

My hydro coil is 20 x 20 x 3.75" double pass. If i place it just under the first penetration it will leave me only 4.25" of clearance. Its this enough clearance?

beenthere · 10-31-2009, 06:51 PM

More would be better. But, it should be enough. providing that you add enough return air to the system.

If it interferes with air going to the first penetration. You may have to add a vane. But, you will probably be ok.

yuri · 10-31-2009, 08:22 PM

Let us/me know when you have installed that coil. I would test the temp rise with the coil installed but NOT the plumbing attached in case you need to remove it. We can tell you how to check the temp rise thru the furnace to see if it is okay. I have also found the specs and info how to tweak the low speed continuos fan (custom config) so it is better than the 50% setting from the factory. The higher it goes the more power it uses.

Good Luck

mogmen · 11-01-2009, 09:07 AM

Beenthere and Yuri,

Thank you both for all your help. I really appreiciate it.

I will let you know once i have the coil installed.

Assuming that this will work, I will need to tap into the furnace control to control the furnace blower without it firing the gas burner.
Originally i had planned to control my project with a direct automation PLC. However, trying to keep this a simple as possible i think i can do it with aquastats and relays. I am assuming i can gain access to just the blower control while isolating the burner as they do in the AC mode. There i go assuming again. Is this possible?

Thanks again for all the help

.

Take care,
Ed

yuri · 11-01-2009, 10:29 AM

The ONLY thing you can do is energize the G terminal on the circuit board thru the thermostat to run the fan continuosly. We can work on the speed of that later. That is a VERY expensive circuit board and anything you add can cause a backfeed and damage it/start the A/C in the winter and other bad events. I would just put your thermostat to ON and use it that way. A ECM motor only uses 80 watts on low speed and it is good to circulate the air in your house anyway. You cannot tap into the logic/operation of the circuit board. I would run the boiler and circulating pump off its own thermostat. KISS Keep it simple stu**d is my motto. I custom made a electric furnace wood furnace setup once. Took 4 hours, 2 thermostats and 11 wires and some relays. Not something that can be described over the internet.