Need help improving heat to slabs

stumblinhorse

The slab zones in my system struggle to warm up. I have an OWB and a propane boiler. The propane boiler is dialed back during the winter months and only turns on if the OWB water temp drops below 120. OWB is set 165* on 185* off(all temps in post are F). Water from the OWB is a closed system thru a heat exchanger and not tied directly to the heating system. In the main boiler room I have 3 zones and an extension to the basement utility room. On that extension the water goes thru another heat exchanger and a mixing value to lower the temp for slab. There are 2 zones on that extension, 1 for the basement of the house and 1 for the garage. Pictures provided.

When the temps are cold the water returning is very cold, this pulls the temps down going into the slabs, especially the return from the garage. I set the thermostat for the garage at 50. I set the thermostat for the finished basement at 66. On cold days the basement cannot get up to temp when the garage heat is on, as the water to the basement zone never gets above 105 or so.

Not sure whether there are other issues as I am the second owner and was not around for the install, so the tubing might be too deep in the floor as I notice the floor in the basement doesn't get much above 70 except close to the utility room.

So my questions is what is best to do. The Taco 007 is kind of loud so maybe the flow is not good. Not sure of age of the pump. Temp coming into heat exchanger is 165 and leaving at 155. Zone water entering the heat exchanger is 80 and leaving at 105(right now it is cold outside, -19*F). Return temp on Garage zone is 75* and basement is 85*.

Not sure where to start. I can replace the pump to see if that helps the delta T. Mixing valve is turned to max so it is not doing much in this right now. Larger exchanger? Garage zone is always going to be colder return. Do i need to separate the zones? Both zones struggle to get to thermostat setting. Looking for advice on what to design and plan. Thanks in advance for any help.

Jamie Hall

I think you are going to have to split the garage zone from the basement zone, and run them separately. The garage has very different temperature requirements from the basement, and kind of hard to get both of them right at the same time on the same zone.

Ironman

Agreed, you should have them on separate zones. That HX also looks like it might be on the puny side.

How many btus are you needing on the basement? On the house? If you don't know, give the number of tubing loops on each.

Zman

The most common issue I see with OWB installs is undersized piping for the boiler to the house. In your picture, the HX looks pretty small and the mixing valve is likely a high resistance model.

Would you be able to sketch out your piping including pipe sizes and lengths? Also include the models of the pumps and HX.
If you are able to measure the temp difference between supply and return on your pipes, that is a great troubleshooting aid. Shooting the pipe with a little IR gun works pretty well, a piece of tape on the pipe eliminates reflectivity and gives you a more accurate read.

stumblinhorse

The picture represents the extension line off the main system. My OWB pipes in with the big pipe to a massive HX in the main boiler room upstairs. There are 3 total pumps on my system, they are all Taco 007, one in the OWB runs 24/7, another one for the main level of the house which is 3 zones (including DHW and 2 zone baseboards), and the extension to the basement is about 10'' of 1" copper and back (it is directly below the main boiler room).

For tubing loops I assume that is one of my problems. The system is older and I would suspect should have been done with more loops. Both are 5 loops. My guess is that current install would be higher in the concrete and more loops. Both areas are about 1200 sqft rectangles.

Solid_Fuel_Man

Can you draw a basic picture of what you mean. I'm not sure why you have 2 heat exchangers if you already have a massive one. 

My first thought is the 007s are too small for the required head of a typical radiant floor. Generally.......a 0015 is used (high head low flow) vs a 007 which is a medium head medium flow circulator. 

stumblinhorse

Solid_Fuel_Man said:

Can you draw a basic picture of what you mean. I'm not sure why you have 2 heat exchangers if you already have a massive one. 

My first thought is the 007s are too small for the required head of a typical radiant floor. Generally.......a 0015 is used (high head low flow) vs a 007 which is a medium head medium flow circulator. 

I have 2 heat exchangers because the massive one allows the OWB to be closed from the rest of the heating system. It delivers between 160-180* water to a large heat exchanger. That transfers to main in-house boiler lines. When any zone is calling for heat the Taco pump is running and the water in the main boiler lines are between 160-180. The second heat exchanger is dropping that temp to feed the zones that are in a slab, basement and garage. Why they did a mixing valve and a heat exchanger I am not sure?

There is not a lot of distance being fed by any individual 007. The main level has 2 zones of baseboard and 1 zone DHW and then the small 8-10' drop to the basement to the other HX. The second pump has 2 zones of 5 loops each in the slabs. And the third pump runs the heated water from the OWB to the house and back, 50 ft each way.

stumblinhorse

So upgrading to a 0015? Good place to start? Or maybe a 007e as a half step?

Solid_Fuel_Man

You really should draw a diagram for us to understand how best to help. Just changing circulators etc isnt what we do here. 

Yes, a 007 is generally not enough head for a typical 1/2" x 250-300' radiant loop slab. 

stumblinhorse

The slab system is pretty simple. It is a completely closed system. Water comes down from the main boiler, 8-10’ of 3/4” copper into the HX. The water on that line pretty much stays above 155 from October to May.

The closed system for the slab, you can see 98% of it in the picture. Only thing not visible is the manifolds and valve for the garage slab at ceiling height. But it is identical to the one in the picture for the basement. The T left of the 007 goes down to lower manifold and up 5’ to the garage manifold. Return from the basement slab you can see the top of the manifold then the valve and up to the mixing valve. T’ed in before the mixing valve is the return from the garage manifold (valve same as basement manifold not visible). Top line coming into mixing valve comes from expansion tank from HX. That is everything.

So I hope that is easier than a drawing. I am on an iPad so drawing is not easy without installing a new app 😀.

Robert_25

Is there glycol in the radiant slab system? That is the only reason I can think of to have that small heat exchanger in there. If not using glycol, I would remove that small plate exchanger and see what kind of temperature difference you get from the supply and return connections to your radiant manifolds.

stumblinhorse

If I remove a HX completely I am not sure that I could keep the temps going into the concrete <120 all the time. Those supplies get to 180 sometimes.

Robert_25

stumblinhorse said:

If I remove a HX completely I am not sure that I could keep the temps going into the concrete <120 all the time. Those supplies get to 180 sometimes. </p>

Don't you have a mixing valve for the radiant system?

stumblinhorse

Yes, but if return water is above 120, the mixing valve can’t go any lower than the return temp. So 180 in and the delta t is 30 or even 40, I am still 150.

hot_rod

stumblinhorse said:

Yes, but if return water is above 120, the mixing valve can’t go any lower than the return temp. So 180 in and the delta t is 30 or even 40, I am still 150.

120 return from a radiant slab? That would be unusually high. Ideal surface temperature is 80- 82°F which would get you mid 20's BTU/ sq ft. 105- maybe 110 should be plenty for a residential slab. Unless it is 6" thick with tube at the bottom?

stumblinhorse

Yes I agree that would be too hot. If I remove the HX I would would be putting 150-180 water into the slab. Maybe I need a happy medium, a little bigger HX? Right this minute, I am putting 105 into the slab and getting return of 80. Slab doesn't get warmer than 70-72, only 80 in the first few feet of the manifold. So not sure what to try or what the problem is... The tube might be at the bottom. But I hope not, seems like people would know better. Could be no insulation under the slab... Or my circ pump might be failing or not strong enough. Basement never warm enough on cold days. And we get cold days, a lot of them.

stumblinhorse

Robert_25 said:

stumblinhorse said:

If I remove a HX completely I am not sure that I could keep the temps going into the concrete <120 all the time. Those supplies get to 180 sometimes. </p>

Don't you have a mixing valve for the radiant system?

Yes, but if return water is above 120, the mixing valve can’t go any lower than the return temp. So 180 in and the delta t is 30 or even 40, I am still 150.

Solid_Fuel_Man

I honestly have no idea what you mean. 

Only thing I can figure is someone undersized the small heat exchanger ge to act like a mixing valve.....

Draw a picture in paper, then take a picture of your drawing. No app needed 

stumblinhorse

I replaced the pump with a 0015e and that lowers the water temp in the lines. So I think the heat exchanger is either plugged or not big enough. Love the new pump,tho, so quiet. Going to just remove it and tie into the rest of the house. Then use the new pump in the main system.