Temp loss

[adcman]

Greetings all, I have a OWB connected to a presurized system with cast iron radiators. I have the boiler running to the heat exchanger, then to the presurized system. My water temp coming into the exchanger is 170, but I am not gettting the water over 130 at the radiators. Everything is new, put in this fall. I use to get 170 at the radiators, no problem. Could it be my pump is not putting out enough flow or is it more likely I have a clogged heat exchanger? The pressure stays at 20 lbs, and I have no air in the radiators. I have noticed that I seem to be overheating (lots of steam out of the overflow) at the boiler more often. I guess I could change out the pump first, but thought I would ask the experts if there was an easier way to determine which is causing the problem. The water going in top the exchanger is hot, but the return is just warm. Thanks

 

[jebatty]

Could be several possibilities. I've used a plate hx in the past, and am aware that efficiency can decline if not cleaned regularly. Did you notice a gradual decline in heat getting to your house radiators, or was the decline sudden? What are the specs on your heat exchanger? I assume a flat plate: mfr, # plates, size, inlet/outlet size. Do you have a filter on either or both sides of the heat exchanger? How long has the hx been in place? have you ever pulled and cleaned it? If more than one season and if you haven't cleaned it, I would recommend pulling it and cleaning it before focusing on a circulator problem.

 

[adcman]

The exchanger is 3 months old. It is a brazed plate 350,00 btu an hour. I really did not notice a slow decline, seems like it was a bit sudden, but I am not sure. I do not have filters on either side, I do have a y strainer on the return side. The temp difference was only 2 or 3 degrees a few weeks ago. Water in at 170, water at the radiators 168 or sometimes even 170. The steam at the boiler has me pointing at the pump, but I may be wrong.

 

[jebatty]

A wye strainer or better yet, an actual filter, really needs to be on the boiler to hx supply side to prevent debris from getting into the hx. Similarly on the house supply side to the hx. I hope the hx was installed with isolation valves so that it can be pulled and pressure/acid cleaned, if not now, then annually in the future.

Not necessarily related to your problem, but a 350,000 btuh rating on a heat exchanger is meaningless without knowing for that rating the approach temp, gpm flow rating on each side, and pressure drop at specified flow rates. For example, I doubt your house has a heat demand of 350,000 btuh. What you need is the selection table for your hx. With the additional info from the selection table, plus pump head/pressure drop for the balance of the system on both sides, it becomes easy to determine both whether the hx was properly sized and what circulator you need to meet heat demand.

 

[adcman]

I went with the larger exchanger due to the 140 year old no insulation farm house, bug heat loss so I went larger than normal. I do not have isolation valves, but hindsight being 20/20 I will install asap. I guess I will start by removing and cleaning the hx. I have 1 inch copper in and out connected to the hx and 1 in pex coming in from the boiler. I also will add a filter to the supply side from the boiler, again hindsight. I thought that maybe the boiler water level got lower than the pump during the night, and caused damage to the pump. I guess I better start learning about cleaning the hx. This project has been way more work than I ever bargained for. And I keep learning the hard way. Thanks for the help.

 

[adcman]

After giving this some thought, If the boiler is steaming outside, then the water temp inside the boiler has to be 212, the thermomometer is on the supply side before the ater reaches the hx. The water shows 160 and the boiler is still steaming. If the pump was working correctly shouldn't the temp show 200 or better? Or would a clogged hx give me the same reading? The return on the hx shows 130 so it would stand to reason that some water is flowing through, which should make the temp coming in before the hx, much higher than 160. I'm confused.

 

[adcman]

Well I switched out the pump, now we will see what happens.

 

[Gooserider]

Sounds like it could be a chunk of crud broke loose from someplace and has partly clogged the boiler side of the HX - if some flow is getting through, but not enough, you would get a high temp drop across it, as the loads pulled as much heat as they could out of what did get through... It might also cause more of a drop in your lines, again a lower flow volume = fewer BTU's in the line to begin with, and the loads pulling just as many BTU's out leaves less in the end....

Could also be a partially damaged pump. Have you seen / heard any signs of cavitation at the pump motor??? This is a common problem w/ OWB's, as they often have trouble maintaining the required NPSH to keep from getting flash vaporization in the pump intake, especially when using high head / high volume pumps....

Lastly, you might want to verify that you don't have any air caught in the system, as this can also cause flow restrictions...

Gooserider

 

[adcman]

Thanks for the reply, I switched out pumps, no diffference. Today I willl start flushing the hx. I did seem to get about 5 degrees more by tapping lightly on the hx, so I guess thats the issue. Funny though, the water at the boiler was crystal clear. I filter the water before it goes into the boiler with a whole house filter, but I am seeing that it might not be enough. I do have y strainers on the lines, but I might have to add filter there also. Does anyone know the concentration of muratic acid to use when flushing, or should I just use vinager?

 

[Gooserider]

This thread from the "tidbits" sticky has a lot of good info on the care and feeding of heat exchangers. If you do a search on "Heat Exchanger Cleaning" you will probably also find some other good info - As I recall a couple of our pro members had a commercial product they liked which was specifically intended for cleaning them, when used in accordance with directions....

I would note that you might just need to backwash the HX - it sounds like you might have just picked up some kind of debris, like a solder glob or a chunk of teflon pipe tape, and it might flush out fairly easily. Chemical scale buildup seems to be more of a problem with HX's used for DHW and so forth where the water is getting constantly renewed. In boilers you keep recirculating the same water over and over, so it will usually just do a light initial reaction and then be pretty stable after that, as long as the water chemistry is right.

Have you had any water testing done on the boiler water? You might have some kind of out of whack chemistry, such as bad pH that might be causing your water to be unduly corrosive, in which case you could have corrosion in one part of the system leaving deposits in another....

Gooserider

 

[adcman]

Thanks again, here is where I am at. I installed two boiler valves, and isolation valves, hooked up a simmer pump in a 5 gallon bucket, with 2 washing machine hoses. I ran a 50/50 solution of water and vinegar through the HX. Worked like a charm. The color of the water thast came out, was similar to a dark beer. I ran the soution for about 40 minutes. I ran the liquid backwards,(flow going through the return lines back out the supply line). I did this on the boiler side of the HX only. The radiator side has barrier pex installed and I am hoping no problems will occur there. It seemed I was buring way too much wood and the house was still cold, now I know why. I did have my water tested and it came back fine This forum is priceless when it comes to the knowledge you guys have and share.(gives me a reason to believe the internet can be used for good) I hope I learn enough to help someone else, like you guys helped me, along the way Thank you again.

 

[jebatty]

Let us know if your problem is solved. Good luck.

 

[adcman]

Problem solved! Thanks Again.