Modifying distribution to radiant floor zones

[Frank Lartone]

Hello,
If anyone would like to offer some ideas that I can implement, I would be grateful.

I have a 3350sq house with an approx 2000sqft walk out basement. House has full radiant floor on the upper two levels and the basement has no dedicated heat supply. The basement stays in the upper 50's typically as the 3/4" copper hydronic pipes feeding the zones are exposed and although the joists are insulated with fiberglass, enough heat escapes the floor above to moderate the cellar temp.. The radiant is divided into 5 zones. This was a DIY from 20 years ago. A Monitor MZ25, wall hung, condensing boiler has been in place since built. It has been struggling with various issues and last night the igniter stopped functioning. It will not be repaired as there are combustion chamber fractures and today it was removed.

I have a Westinghouse WBRCLP140 that was purchased 2 years ago, but has never been commissioned. I would like to put this boiler in the system. I thought , when I purchased it that the 10:1 turn down ratio would make a good fit. I don't know now. The more I read the less I know.

Calculated heat loss from walls windows and ceiling, including basement is approximately 51Kbtu. This does not include any loss from air exchange. The 5 zones are approx, without account for air infiltration, 7.4Kbtu, 5.4Kbtu, 4.3Kbtu, 10.5Kbtu, 13.5Kbtu. The basement adds 9.4Kbtu.

Each zone is 4, 5 or 6 loops of 1/2" pex on top of plywood sub-floor in 2" gypcrete. Typical loop is 100'-140', IIRC run off of Wirsbo mainfolds with each loop having an adjusting valve. The main manifold off the boiler is regulated by Taco zone valves and zone control.

So my question comes in regarding water distribution. I don't have much of a grasp on this part of the system, but I would like to add to it if that is appropriate (both my grasp and the hardware). There has been no mixing valve or primary/radiant loop or close proximity Ts or buffer tank or any kind of water diversion in the system so the heated water has been fed directly into the distribution manifold that sits next to the boiler. The old boiler had a circulating pump and there was another circulating pump prior to the zone valves. I guess the house has typically been comfortable, but from what I am reading lately, it seems the water distribution isn't designed as it should be.

The previous boiler was not modulating and there were times when short cycling was an issue. Output temp has been run between 117F and 125F over the years. Last year I had been opening a couple zone valves manually because the wax motors failed. This was kind of a good thing as the short cycling was somewhat mitigated, I suppose because it made a larger zone by combining them.

I would like to get this straightened out as best I can, even if the distribution isn't perfect. I can do the installation with some good advice. Once I have it set up as best I can, I'll have someone come in and inspect the gas fittings and get the initial fire up.

Here is the existing distribution with a Taco 007-F5. There is a Grundfos Type UPS 15-42 F I took out of the old boiler available as well.

Thanks again for any interest and help.

 

[Houptee]

I think you need to add closely spaced T at the connections to the new boiler. Not sure why you had 2 circulators I think one is all you should need maybe that is why the original did not work properly there was too much head and flow rate?

 

[Sponsor]

 

[Houptee]

Also check or just replace your cold water inlet backflow preventer and feed pressure valve. The system should be max 12 psi and the expansion tank is good or just replace it since its old they are inexpensive.

 

[Frank Lartone]

Also check or just replace your cold water inlet backflow preventer and feed pressure valve. The system should be max 12 psi and the expansion tank is good or just replace it since its old they are inexpensive.

Thanks for the comments.

One of the two circulators was built into the boiler. The new boiler has a built in pump as well. These are to drive the primary loop, I assume. I did a primary loop with closely spaced Ts. I put an air scoop and expansion tank in the secondary loop in front of the circulator which is in front of the zone valves. The back flow preventer and the 12 psi pressure valve were fine and were re-installed.

I should have this fired up tomorrow. I will see how it goes with a set output temp around 122F while I get my head around the outdoor reset. I think I will leave the smallest 2 zones manually open and not use their tstats for the short term. Later I may see how I can better integrate some of the zoning and tstats to balance the zone loads a little bit. I think I could purposefully and efficiently manage to manipulate the system into 4 zones with fairly equal loads for each zone.

 

[Houptee]

I don't see in your picture a primary/secondary loop, all I see is the one loop to the zones and the cut off pipes where the old unit was.
Usually a primary loop is going thru a brazed plate heat exchanger and back to the boiler with a circulator.
A secondary loop would come off the heat exchanger with a separate circulator.
So If you can post a picture of how you piped the new unit that would help clarify what you did.

 

[Frank Lartone]

That was the original state of the plumbing in the picture. I will post one with the reworked pipes later. I was a little squeezed for space so the piping was a little challenging. Getting 6" on either side of the Ts and getting the expansion tank in and getting the circulator enough length of straight before the zone valves....all tight. Also, while I put in shut offs and drains, there may not be all that are needed to easily service the unit for flushing.

I am not against reworking some thing after the heating season, but it will be what it is for now.

 

[Dana]

The very low pumping head of the fire-tube heat exchanger in the WBRCLP140W the means it probably doesn't need (or even want) to be plumbed primary/secondary, no closely space tees necessary. It's the same heat exchanger used in the UFT series heating-only boilers, where "No Primary / Secondary Piping Needed" is one of the main selling points.

If plumbed with a closely spaced tee hydraulic separator the primary loop is almost guaranteed to be over-pumped, unless going with a very small pump like the Taco-003 or an Aqua Motion AM55 in "PERMANENT NIGHT SETBACK" mode. When over-pumped the delta-T at the boiler is going to be very small.

It might be useful to use a smart pump a constant-pressure operating mode, such as the Taco VR1816, which works pretty well for systems with zone valves. If a Taco-007 was providing enough flow, the VR1816 will too but it'll be "nicer" to the zone valves & plumbing by not over-pumping when only one or two zones is calling for heat.

Is the outdoor temperature sensor option implemented?

 

[Frank Lartone]

Still working on getting the system functional for the time being. Hopefully in the morning.

The only pump in the primary loop is the pump inside the boiler. The Taco-007 is ahead of the zone manifold, pretty much serving as it did originally, but moved to accommodate the other piping, so I assume this won't over pump the primary?

I am sure my overall pipe work is a little oddly laid out. When the old boiler came out it left me with a relatively tight space to work with. The water heater and gas lines were very much in the way and I wasn't willing to lose the gas and hot water at the start of the project, not knowing how long the new installation would take. If I were able to remove them at the beginning I would have head a lot more room to pipe in the new boiler, especially considering I was now adding the DHW piping from the boiler.

The outdoor reset is not set up as of yet.

I installed the system 20 years ago and I think the layout of the radiant side of the system is not too bad. I did not realize at the time how much went into the supply and distribution side. I guess I just sort of thought it was about constantly moving warm water through the tubing. I certainly didn't spend much time thinking about return water temp, although I did understand carpeted areas can be problematic. I am trying to get a better handle on it.

 

[Dana]

The internal pump & three way valve is fine- it is appropriately sized (indeed purpose-designed) for the application.

I hadn't realized that major difference between their combi-boilers and (closely related ) space heating only boilers. I apologize for disseminating that disinformation! A caution on page 37 of the manual reads:

Use at least the MINIMUM pipe size for all appliance loop piping (connecting appliance to and from the primary/secondary connection). DO NOT pipe the appliance in any configuration other than primary/secondary. All piping methods shown in this manual use primary/secondary connection. This is to avoid the possibility of inadequate flow through the appliance. Using less than the required minimum pipe size and piping in anything other than a primary/secondary installation could result in system problems, property damage, and premature appliance failure. Such problems ARE NOT covered by product warranty.


The Taco-007 is probably overkill, but should still work. It chews through 8-10 times the electricity of an appropriately set up ECM drive "smart" pump like the VR1816, but there isn't a burning need to swap it out from a system functionality point of view.

 

[Frank Lartone]

It is up and running with primary secondary. It is 9°F outside so heat is a good thing.

The closely spaced Ts are doing what they are supposed to. The heated output water moves to the zone manifold and the return water has a pretty good ▲T using the hand test. Output is set at 125 and the return is significantly cooler. Not all zones are keeping up, but the boiler heat has been off for ten days. It seems as though all of the floor loops are moving water, but I will need to check all of the manifolds and see how even the return lines feel. One 7 loop supply manifold I checked was feeding some loops a little warmer than the others. They are Wirsbo zone manifolds and each loop has an adjustable valve, but I have never actually put in the work to dial them in.

If anyone can offer suggestions on dialing in the loops in the zones I would like to know how to go about it.

 

[Dana]

It is up and running with primary secondary. It is 9°F outside so heat is a good thing.

The closely spaced Ts are doing what they are supposed to. The heated output water moves to the zone manifold and the return water has a pretty good ▲T using the hand test. Output is set at 125 and the return is significantly cooler.

To hit mid-90s efficiency most boilers need an entering water temp (EWT) of 115F or so. If the return water temp from radiation is a lot cooler than the EWT at the boiler it might be worth dropping the speed on the internal primary pump. If I read the manual correctly the default speed is "3", the highest speed, which is what would deliver the lowest delta-T.

Not all zones are keeping up, but the boiler heat has been off for ten days. It seems as though all of the floor loops are moving water, but I will need to check all of the manifolds and see how even the return lines feel. One 7 loop supply manifold I checked was feeding some loops a little warmer than the others. They are Wirsbo zone manifolds and each loop has an adjustable valve, but I have never actually put in the work to dial them in.

If anyone can offer suggestions on dialing in the loops in the zones I would like to know how to go about it.

Don't guess, MEASURE the return water temperatures from each zone separately. A $50 infra-red thermometer is accurate enough if pointing it directly at PEX at very close range (or even touching the pipe), but won't correctly measure the temperature of copper or other shiny metals. If a zone isn't keeping up and has a much larger delta-T (lower return temp) than the others it needs more flow. For any of the zones you'd be looking for at least a 5F delta, 10F better when the supply temp is 125F. Really tiny delta-Ts is an indication of being over pumped- too much flow.

You may have to just raise the temperature of the boiler for all zones to keep up. Play around with it a bit and keep notes as to the outdoor temperature and water temperature when it's just barely keeping up. If it won't keep up at single-digit outdoor temps with the EWT of the boiler under 125F it will definitely be worth installing the outdoor sensor and tweak the programmable "outdoor reset" curve to where it just barely keeps up at all outdoor temperatures, using the lowest possible output temp. That way it will be in condensing mode whenever possible, yielding the most stable indoor temps and highest combustion efficiency. Having notes of what the water temps needs to be to keep up at some corresponding outdoor temps is enough information to set the reset curve pretty close right away and just fine tune it from there.

 

[Frank Lartone]

Thanks for the comments. It seems have one very stubborn zone. I'll have to investigate a bit. Input manifold temp is about boiler EWT, but the return manifold is much cooler and the floor is uneven in temp. I opened the bleeder, but it appears to be clear of trapped air.

What's the best way to verify water is pushing through all of the loops? The return manifold at the zone has a 1/4 turn valve with a hose thread output. If I connect a drain hose to this and open the valve and allow water to escape while make-up water is added to the system, that should clear any vapor lock that might exist in the loops I would think. Is this a reasonable exercise?

 

[Houptee]

When you first fill the loops you have to go to the pressure reducing fill valve and depending on the brand there is a lever or something that lets you fast fill the loops with higher water pressure and flow. You open that return drain valve with a garden hose hooked to it and fast fill the system as you purge air out the garden hose. Then when it stops farting and you have steady water coming out close the return drain valve and put fill valve back to normal fill mode (they come factory pre-set at 12 psi system pressure). Then run it with boiler on. You should have some automatic air bleeders that get rid of residual air if placed in proper locations.

 

[Houptee]

To adjust each loop some radiant manifolds have built in flow meters on them and you adjust so all loops have same flow rate.

 

[Frank Lartone]

When you first fill the loops you have to go to the pressure reducing fill valve and depending on the brand there is a lever or something that lets you fast fill the loops with higher water pressure and flow. You open that return drain valve with a garden hose hooked to it and fast fill the system as you purge air out the garden hose. Then when it stops farting and you have steady water coming out close the return drain valve and put fill valve back to normal fill mode (they come factory pre-set at 12 psi system pressure). Then run it with boiler on. You should have some automatic air bleeders that get rid of residual air if placed in proper locations.

Thanks. The lines are filled, but I was wondering about pushing water through only one zone. Your description pretty much answers the question. I was wondering if the make-up water @ 12psi would be enough to clear any air lock that might exist in one or more of the loops in a single zone. Other than an air lock, I don't know why the stubborn zone (6 loops may total 900 linear feet or so) isn't heating well.

 

[Houptee]

Just close all those manifold ball valves and only run the one stubborn loop see if it clears it and starts coming back hot on return. You can leave the zone valves alone doesn't matter if they are open because you shut off the ball valves. Then one by one open each loop slowly.

 

[Dana]

If it's possible to isolate all other zones with ball valve it should be possible to push water through just the mis-behaving zone, which is the classic way to purge air. If 12 psi is sufficient pressure to fill the system, it's sufficient pressure to purge the zone.

When adjusting zone flows you do NOT want to make the flows all equal unless all zones have the same heat load. A 1-loop zone doesn't need anywhere near what a 6 loop zone needs, and giving them the same flow becomes an over/under pumping problem. A better starting point is to set the delta-Ts to be equal, and only bump up flow on a zone if it's not keeping up.