Water to Air Heat Exchanger in Furnace problems

[dirtyedge]

Although the OWB is 150' feet away and the pipes do run uphill a little to the house, we installed the pumps about 2' off the ground in the basement to insure that we were below the boiler tank. Central boiler recommends that if the pumps are installed inside the basement that they are 4' below the top of the boiler.

Could someone help me with slowing down the fan speed. I currently have 2 thermostats wired for each furnace, the second tstat is wired by taking Red (existing) to REd(owb tstat) and Green (existing) to White(owb tstat). With this setup I had to disconnect the yellow wire on the furnaces to prevent the AC from kicking on.

 

[mtfallsmikey]

The fan speed tap(s) go to the HV side of the fan relay, usually:
red=hi
black=low
yellow=med.

Find where the fan motor goes to on the relay, change speed taps.
Yes, cold/cooler air will reduce the heat output of the HX, return air should be in the 65-70 deg. range to work properly.

Also, don't have to disconnect the Y wire to condenser, just turn off the breaker/disconnect switch.

 

[i'mstihlaguy]

I replumbed the HX's to run in series again, last night. I think a main part of my heat problem is air trapped in the lines.

Which leads to my next question, I have 150' of 1 1/4" thermopex feeding a taco 014 pump to 1" pex to both HX's in the furnaces in my basement, is there any chance that this pump is not getting the amount water that it needs from the boiler?

I also have a 150' of 1" thermopex feeding a second taco 014 that goes into 1in pex that feeds a 30plate water to water HX for a indoor pool. When trying purge the air out of this line I put a hose on the boiler drain which is at the high point in the system and closed the return valve off and the water comes out of the hose very slowly, maybe a gallon every 1 min. These pumps are supposed to flow 32gpm.

The furnace side flows faster than this but still is not as fast as what I would think it should.

When purging the air can I just leave the boiler drain open? I did that last night and sometimes the system would run for a couple of minutes before water trickles out. Before I switched the HX's back to running in series I shut one valve so all the water was running through one HX and I was seeing 125deg air out of the plenum but now I with both in series I only have 95-105deg air out of both of them.

I guess for now I will try the techniques mentioned in previous posts and see what I can do.

Maybe I am missing something but shouldn't you be getting flow rates close to the pump's rated output regardless of whether there is air in the system? Doesn't the air just create voids that inhibit heat trasfer? The water still has to circulate through the loop as long as the pump has proper inlet pressure. I would check each pump's output as close to the pump as possible (before the water gets to any HX). May not be the solution but it wouldn't hurt to verify.

 

[Slick]

Yes you would get flow but I think most are worried there is air trapped in the exchanger....then you get no hot water in part of it, then less heat output.

 

[Marklambert61]

BTU's

You need to consider basic thermodynamics...The pump aint the problem

Flow through a 1 1/4 pipe is about 12 GPM flow

Max temp drop a cross your coil should never exceed 30 degrees

That will yield you about 100,000 BTU's


You need a lots more volume of water....

Also so your best bet for pluming this monster is is in series with 3 way zone valves controlled independently by your thermostats. Keep you incoming water temp as high as posible 170 -180 degrees



Mark

 

[i'mstihlaguy]

You need to consider basic thermodynamics...The pump aint the problem

Flow through a 1 1/4 pipe is about 12 GPM flow

Max temp drop a cross your coil should never exceed 30 degrees

That will yield you about 100,000 BTU's


You need a lots more volume of water....

Also so your best bet for pluming this monster is is in series with 3 way zone valves controlled independently by your thermostats. Keep you incoming water temp as high as posible 170 -180 degrees



Mark

I am no expert by any means. Just asking. How do you get 12 gpm as an absolute number for 1-1/4" pipe? Isn't it a factor of the pump/motor/torque that is pushing the fluid as well?
Dirtyedge said,"When trying to purge the air out of this line I put a hose on the boiler drain which is at the high point in the system and closed the return valve off and the water comes out of the hose very slowly, maybe a gallon every 1 min."
Both HX are in series now so if he closed the return valve, shouldn't the entire pump's output be coming out of the drain?
I agree he needs more flow (gpm) thru the HX. If he's only getting around 1 gpm out of the boiler drain then I thought maybe the pump output was too low or there's a restriction somewhere. Again, not an expert.

 

[Marklambert61]

Pump in a boiler

I am no expert by any means. Just asking. How do you get 12 gpm as an absolute number for 1-1/4" pipe? Isn't it a factor of the pump/motor/torque that is pushing the fluid as well?
Dirtyedge said,"When trying to purge the air out of this line I put a hose on the boiler drain which is at the high point in the system and closed the return valve off and the water comes out of the hose very slowly, maybe a gallon every 1 min."
Both HX are in series now so if he closed the return valve, shouldn't the entire pump's output be coming out of the drain?
I agree he needs more flow (gpm) thru the HX. If he's only getting around 1 gpm out of the boiler drain then I thought maybe the pump output was too low or there's a restriction somewhere. Again, not an expert.

12 GMP is just an estimate I based on diameter and distance and pump stated....

You need to keep in mind that you not really pumping in the true since of the word we are simply circulating in a closed loop. If we were truly pumping we would be developing a head pressure and forcing water in large volume. In the case of boiler there is almost no pressure developed. Pipe diameter and distance have a huge effect on flow rates there are other factors also ie: Restrictions like fittings and yes pump size, however if you doubled the pump size in this case you would only gain 3-5 GPM as an estimate only.

Mark

 

[mtfallsmikey]

There is a max flow rate thru all sizes of pipe, assumption is correct. HX coil is piped in a parallel fashion, lots of ways air can get stuck. I would think you have enough pump capacity to do this....I like lots of isolation valves, drains, etc, for venting, etc. A good power purge from a water hose is probably needed.

 

[oneoldbanjo]

Well this may be a little hard to believe....I know it was for me until the day I actually saw it occur. But air trapped in a high spot in a water line can cause a huge reduction in flow. When air is trapped in a high spot in the line the fluid must flow beneath the trapped air in order to get past the trapped bubble. Depending on the size of the bubble it can almost completely block flow by reducing the amount of area that the fluid can flow through. If the pump is a low pressure and/or low volume pump it may not provide enough pressure or flow to push the air out of the high spot and purge the line of trapped air.

I am a Civil Engineer here in Kentucky we have lots of hills and valleys and we install a hydrant or air realease valve at every high spot in the line - the only exception being a very small rise with a very low slope where we are sure the air can be pushed out of the line by the water flow. Although I always believed that trapped air was a problem I had actually never seen it occur until one day in Butler, Kentucky. We designed a water booster station and a new water line that would pump water up to a new water storage tank on top of a big hill. The water plant would take water out of the Licking River and process it into drinking water and then the booster station would pump it to the storage tank on top of the hill. When they were done making water the booster pump would shut off and then the water would flow by gravity back into town to supply the residents with water. Just after the water main left the booster station there was a small rise of about 30 feet and then the water line went back down a hill about 50 feet prior to going up a 200 foot tall hill where the water tank was located. Everything worked great for about 8 years and then the Mayor called me and said they were having trouble - the booster pump was having trouble getting water up to the tank and they were making water at their normal speed - but the booster pump was getting it up the hill really slowly. Then after the tank had water in it and the storage tank was supplying water to town the pressure was way down and resident were complaining about the low water pressure. I went out and everything in the booster station and storage tank appeared to be fine. The Mayor told me the problem started after they had a waterline break in town and had to shut the system down temporarily. Luckily I suspected trapped air at that point and I opened the fire hydrant we had installed at the 30 foot rise in the field and I did let out some trapped air......and the water system again operated normally. What happens is trapped air can turn an 8" water line into a 2" water line by only allowing water to flow beneath the trapped air bubble (I only guessed at those numbers as an example).

Trapped air in a heat exchanger or PEX tubing can do the same thing. If the OWB pump does not provide enough pressure to push an air bubble down from a large vertical rise - you will have to install an air release valve at the high point to provide a way to bleed the air out of the system.

 

[i'mstihlaguy]

Okay, I understand now. The key is this is a non-pressurized system so the rules are different.

 

[dirtyedge]

Well the fire went out during the day yesterday, which ended up to be a good thing. When I got home from work the water temp was 80 so I started it up again, and once it got up to temp the house stayed at 72, which is the first time it would reach the tstat high level.

I read on another post that they were told to run the pumps for 24 hours before starting a fire to purge the lines. I don't know if this was the trick by having colder water run through the HX's or if it just took the extra time to get the air out but it worked for me.

Thanks for all the help, I still need to slow down my fans but for now the house is warm, and hopefully it will stay that way.

 

[oneoldbanjo]

It doesn't matter if the system is pressurized or not for trapped air - trapped air can still obstruct flow if it requires water to flow around it. The bubble acts kind of like an orifice and forces the water to flow around it and that causes a reduction in the volume of water that will flow. If the bubble is big enough it can be a huge obstruction.

 

[mtfallsmikey]

Facinating story Banj...you need some rep!

 

[Slick]

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

As for as gpm, head, max flow through pipes etc...this link from Taco helped me put it all into perspective about how fittings and different pipes can really add up and how more flow can equal more btu's at the exchanger. I had called Taco for help selecting a pump and he reference met to this....take a minute to do the actual calculation laid out on there and alot more makes sense.

 

[fpc310]

I am having similar issues as some of the others on this thread.

I have a Hardy H4 hooked into a 5 ton coil on my main house furnace and a smaller 16x18 coil for an old furnace in my garage. The system does not circulate unless one of the furnaces is calling for heat.

I now know I made a mistake when I connected these in parallel and not in series. I don't notice it as much since I have a zone valve on the garage circuit though. When both units are running, it seems like the garage is the BIG loser and fights to keep up. I am also installing some purge valves on the high points in the system to get the air out. I do notice a huge temperature drop on the garage unit. The supply is plenty hot though and usually can't be touched without getting burned. The air coming out is luke warm at best.

At this point, I am going through what seems like 2 nearly full loads each day for a 2700 sqft house, 2 car garage, and hot water heater in Ohio temps (20-40 F mostly). This just seems like a LOT of wood compared to what most of you are saying.

Any additional suggestions on "best practices" to get the best efficiency? If I run these in series, would it be OK to not use a 3-way zone? I had that garage unit freeze on me during a vacation once.

Thanks!

 

[Marklambert61]

Need a little more info

I am having similar issues as some of the others on this thread.

I have a Hardy H4 hooked into a 5 ton coil on my main house furnace and a smaller 16x18 coil for an old furnace in my garage. The system does not circulate unless one of the furnaces is calling for heat.

I now know I made a mistake when I connected these in parallel and not in series. I don't notice it as much since I have a zone valve on the garage circuit though. When both units are running, it seems like the garage is the BIG loser and fights to keep up. I am also installing some purge valves on the high points in the system to get the air out. I do notice a huge temperature drop on the garage unit. The supply is plenty hot though and usually can't be touched without getting burned. The air coming out is luke warm at best.

At this point, I am going through what seems like 2 nearly full loads each day for a 2700 sqft house, 2 car garage, and hot water heater in Ohio temps (20-40 F mostly). This just seems like a LOT of wood compared to what most of you are saying.

Any additional suggestions on "best practices" to get the best efficiency? If I run these in series, would it be OK to not use a 3-way zone? I had that garage unit freeze on me during a vacation once.

Thanks!

FPC,

I need more info about your system to really make an accurate comment.

Supply and return pipe size?
Pump type and size?
Length of run of plumbing?
Water temps at boiler in and out, at coils input and outlet?

In your post you said you have a 5 Ton coil that a little puzzling as AC coils are rated by tonnage. Heating Coils are rated by BTU's problem is AC coils are very restrictive to flow of water if use for this application.

Mark

 

[mtfallsmikey]

Mr. Lambert beat me to the post I was about to make! I have my HX's in "parallel", but I use primary/secondary piping methods, which entail using a circ. instead of zone valves. If your primary/secondary loops ( and circ.) are not sized properly, you can have low,or too much flow thru the HX's. pump/pipe sizing is not rocket science, but all work together. We used to accomplish this years ago by using the B&G "Monoflo" piping system, which used tees with diverters built into them. My HX's work beautifully, only mistake was when I used my 007's on the secondary loops, I did not use the IFC model (with built-in check valve) so I have some ghost flow. Not a big deal in my shop, but the fan in the house furnace cycles intermittently because it is a counterflow furnace, HX mounted underneath, and the heat rising from the coil trips the fan control "on". As I've said many times before, pleas get a copy of "Pumping Away" from Dan Holohan at heatinghelp.com. This explains the proper pipe/pump sizing methods.

pleese....

 

[fpc310]

Supply and return pipe size: 3/4 Pex (as recommended by mfr)
Pump type and size: Taco 009
Length of run of plumbing: OWB To House Furnace: 75ft
Length of run of plumbing: House Furnace To Garage: 40ft
Water temps at boiler in and out, at coils input and outlet: I don't have these metrics at this point. I am in need of some inline temp sensors to help me measure this. Any recommendations?

Hardy seams to classify their exchangers by tonnage, but it is in fact a 130K BTU exchanger at 2000cfm w/ 3/4in NPT connections. This one works very well too. The exchanger in the garage is a 120K btu exchanger w/ 1in connections (american royal brand). I have it also hooked up to 3/4 pex using reducers. I know I am not going to get 120K BTU with such small lines, but I was hoping for at least 80K.

Todd

 

[mtfallsmikey]

IMHO, 3/4" mains are too small, the 009 can really ram some serious water thru, that is why it is the go-to pump for OWB use. It may be sending water too fast... even tho I disagree with the practice, you may have to convert to feeding your HX in series, but may move the water too fast. If there is not too much vertical lift, or restrictions (fittings, valves), the 007 would do the job. Your 130K coil is around 11 tons...1 ton cooling/heating = 12,000 BTU. Also, airflow across the coil makes a huge difference in output air temp.

 

[Butch(OH)]

I am having similar issues as some of the others on this thread.

I have a Hardy H4 hooked into a 5 ton coil on my main house furnace and a smaller 16x18 coil for an old furnace in my garage. The system does not circulate unless one of the furnaces is calling for heat.

I now know I made a mistake when I connected these in parallel and not in series. I don't notice it as much since I have a zone valve on the garage circuit though. When both units are running, it seems like the garage is the BIG loser and fights to keep up. I am also installing some purge valves on the high points in the system to get the air out. I do notice a huge temperature drop on the garage unit. The supply is plenty hot though and usually can't be touched without getting burned. The air coming out is luke warm at best.

At this point, I am going through what seems like 2 nearly full loads each day for a 2700 sqft house, 2 car garage, and hot water heater in Ohio temps (20-40 F mostly). This just seems like a LOT of wood compared to what most of you are saying.

Any additional suggestions on "best practices" to get the best efficiency? If I run these in series, would it be OK to not use a 3-way zone? I had that garage unit freeze on me during a vacation once.

Thanks!

Welcome to the site neighbor. I am not an expert but I think you are describing two problems, heat delivery and efficiency and I would treat them as such. Personally I would not fool with parallel zones and the associated valves. I too heat my garage and house but run two dedicated loops. There are three devices on the house loop, heat exchanger in the duct, a side arm for water and a plate for water but they are in series. Not sure if the H-4 has that capability (2 loops) or if you want to dig things back up to change them this time of year but the type of system I have is simple, and works.

I may be over simplistic in my thoughts but to me, basic trouble shooting a hydronic system only requires the most basic of tools, your fingers. If you touch the lines when the fans are blowing though the heat exchangers the temp drop between the feed and return should be hard to disern with your fingers. If you have a huge drop then the flow is low. Low flow could also be OK if you are still getting the required heat from the unit anyway. If there is no discernible drop and you still are not getting enough heat from the unit then you need a larger exchanger or the fan needs to move more air through the one you all ready have. Correcting flow could mean removing air from the lines, a larger pump or larger line. The stove companies are good about getting these things right, most of the time. You can also compare with what people are running and works right. My stove is 60 foot from the house and I have 1" line and a 014 pump. The shop is 10' from the stove and has 1" lines and a 007 pump. On to your your wood consumption question. In these systems the heat from buring goes to four places, delivered to your house, out the stack of the OWB, and into the ground or air from exposed loop lines. If your are thawing the ground above your pipes in any decidable manner that is likely your problem. If you have above ground pipes that radiate heat into the air in non heated areas that is part of your problem. Heat going out the stack is largely unfix-able. You could also be using a lot of BTUs to heat with? When I turned my shop heat down to 55-60 from 70 it makes a couple arm loads a day differance in my wood usage. To heat what you are discribing twice a day loading is not WAY out of line but could be some out of line, hard to tell for sure. To heat your house, garage and water for 6-7 months you need to plan on 10 cords to start out and adjust your cutting, or purchases from there. The Hardy does not have a reputation for being tops in efficiancy but neither should one be LOTs worse than any other OWB.