In floor radiant question on performance.

jfrank

I recently moved into a house with 2 hydronic systems. The main system uses a boiler and baseboard radiant units and all works very well. The addition to the house which is about 10 years old is using a domestic hot water heater driving radiant in floor heat. The workmanship looks great, but I suspect there was no engineering involved when the system was installed. The previous owner warned me that the system didn't perform very well and after living here for a month or so I can attest to his findings. I am planing to update the entire system in 2018 so I don't want to throw a lot of money at this right now and hopefully whatever I do will still be a viable part of the upcoming 2018 upgrade.

I'm not sure if the problem I'm having is due to a failure somewhere in the system or just poor design. I've tried to engage someone locally, but I haven't been able to find someone knowledgeable in system design. Without knowing if the design is functional trying to repair it is shooting in the dark.

Here is the information I've gathered so far.
BTU load: 20K BTU
Heat source: Domestic hot water heater.
Heating loop materials: (~15') 3/4" ridged copper, (3) 90 degree elbows, 3/4" mixing valve, Expansion tank, Back-flow preventer, Wirsbow A2533220 and A2513220 Manifolds feeding 5 loops of 1/2" pex. Each loop is about 300'.
Pump is on the supply side of the manifolds and is a Grundfos UP15-42F

The problem I see is the delta T is 60 degrees. I'm assuming this indicates poor flow in the system. The question is what's causing the problem? Is it caused by a poor design, system blockage, component failure, or possibly a combination of these? Any help or troubleshooting suggestions would be greatly appreciated.

Thanks in advance for your help

Zman

As you have probably already gathered, hot water heaters are not designed to heat houses. In your future upgrades it would be great if both areas could be heated with the same boiler.

You are on the right track in thinking that the high delta t is an indication of low flow. You circulator seems like a reasonable choice for the application. I suspect that the culprit is the mixing valve. Many installers use valves that are designed for domestic water. The have very high resistance and don't work well in heating systems. What is the model and cv rating of the mixing valve?

SWEI

Can you post a picture of the piping and pump(s) near the water heater?

jfrank

I've attached some pictures that may help. You'll notice in the pictures that the hot water heater is in parallel with a wood fired boiler that you can't see. The inlet and outlet to the boiler are both turned off so it's isolated from the system. The only active connection you can't see is from the water supply and back-flow preventer. Also I took a look at the mix valve and found it's a Watts MMV Type T. I suspect it's for domestic hot water as the specs say it's max temp out is 120 deg. I wouldn't think this valve would be needed if the wood burner is not used. I'll evaluate the need for the wood burner further before deciding on a final design for the update.

Thanks

Mark Eatherton

How is the tubing installed? In cementitous materials, or bare naked staple up?

And yes, so long as the wood boiler is not part of the equation, you can probably safely eliminate the mixer completely.

All of my assumptions assume the water heater is doing ONLY space heat, and not DHW and Space heat. If it is doing both, I'd be very careful about exposure to Legionella.

ME

jfrank

The tubing is stapled up to the floor above. I can't see exactly how it's installed, but it does have some sort of reflector / insulation and unfinished drywall under it. You are correct that the the hot water heater is used only for the radiant heat and not DHW. To be safe I think I will replace the mixing valve with a device suitable for the application so that the wood burner could be used if needed. Hopefully the valve footprint will be close enough to install it without a major rework of the plumbing.

JF

Rich_49

You will need a room by room heat loss analysis performed to address what is actually required in each room .

What is your location ? In this upgrade , is your intent to address as many issues as possible , use one source for both Baseboard , radiant , domestic hot water , What is your ultimate goal ?

What is the finished flooring material where the radiant is at present and as Mark asked , is it staple up , embedded , lightweight overpour or something other ?

A proper design regardless of what is there is absolutely necessary to get it right , you already are experiencing the need for that .

hvacplumber7

Start with what rich said. Room by room heat loss calc.
Than figure out the exact type of staple-up you have. Plates, no plates, direct contact, stand off, or ultra fin.
Next figure out exactly how it's insulated and the r-value. Insulated tight against the tubing or is there an air gap.
Next figure out what type of subfloor and floor you have.
All this info will allow us to figure out how much heat is needed, at what temp, and if maybe your heat is going down instead of up.

SWEI

jfrank said:

I've attached some pictures that may help.

That PVC drain line is in the way, so I can't tell how the expansion tank and air separator are piped into the system. The expansion tank should be piped a close as practical to the inlet side of the circulator.

A 3-way valve with a single circulator is not really going to move much through the water heater.

The piping appears like it may be directly connected to the potable water system.

Gordy

What is the btu rating of the water heater? 36k 40gal?

You indicated a load of 20k in initial post. Was this a heat load calc done by you? If so what program?

Can you tell what centers the pex is on? 2 runs per joist bay?

How many square feet is the radiant floor area?

What are the finish floor treatments?


First thing to try, and cheapest is to remove mix valve, and pipe direct. See how deltas fair then, and output. Look for a 10 degree delta for radiant floors is optimal. See if you can achieve this. Piping direct as Mark suggested, and with his caution allows you to get the water temps up also. Say 140 with that particular radiant detail.

I have a feeling that to get a sufficient delta, and output to the space you will need at least 140 SWT.

Zman

The immediate problem of high delta to is absolutely a result of an inappropriate mixing valve. At 4 gpm, the valve has a resistance of about 16 ft of head.
As Mark said, if the outdoor boiler is not going to be used, you could eliminate the valve. Otherwise replace it with one with a cv of about 5 or higher.

jfrank

Thanks to everyone for the great response. By way of a brief recap the system in question is completely separate from the main house and was installed by the previous owner when he built the addition. As an RF engineer I understand the need for a complete analysis of the working environment before any major planning can begin. I do hope to update the entire system in 2018. Over the next couple of years, I plan to gather the data for the rest of the house and create a plan using the Flo Pro software. I will definitely submit the plans for review before starting the actual project as I haven’t been exposed to “fluids” since collage almost 40 years ago. However since the system in the remainder of the house works well I’d like to defer any changes to that area for now and treat this as a standalone problem. I've done the heat loss analysis on the addition and calculated the loss as 19,800 BTU/HR. The calcs. included the doors windows construction type and insulation installed. This is only a one room addition of 960 square feet. The problem I’m having is a very high delta T of almost 60 degrees. I’ve suspected a flow issue but wasn’t sure how to proceed with testing to determine if the problem was due to a faulty device or design. I think Zman probably hit the nail on the head with identifying the mixing valve. I can’t find anything to support the idea that the installed valve was designed to be used for this application. Since according to the manufacturer the max temp out is 120 degrees I suspect it was designed as a type or scald protection for DHW. I won’t be able to test this theory until late next week as duty has called me out for town for a few days.
Here’s a few quick answers to the questions and concerns that have been raised. I do understand the pictures make it look like the system is connected to potable water, but that's not the case. The hot water heater is only the heat source for the radiant heat in the addition. The PVC pipe that looks like a drain is actually the flue for the hot water heater which is a high efficiency unit. The expansion tank is on the hot water side of the heater and has a few feet of pipe, a couple of elbows and the mix valve between it and the pump. I would consider moving the tank before the major upgrade if you think it may be causing this problem, otherwise I will defer it. As to how the tubing is installed I’m going to have to remove some of the drywall to expose it to find out. Again I may not do this until I get the delta T under control and see how the system performs. I will definitely check it out before going forward with the future update. I’m glad you brought this up as it makes perfect sense, but would have slipped under the radar. I’m also planning a little redecorating for this room and hope you can provide some guidance on selecting a suitable floor covering.

Thanks again for all the help. It's much appreciated.

JF

SWEI

jfrank said:

I do understand the pictures make it look like the system is connected to potable water, but that's not the case. The hot water heater is only the heat source for the radiant heat in the addition. The PVC pipe that looks like a drain is actually the flue for the hot water heater which is a high efficiency unit. The expansion tank is on the hot water side of the heater and has a few feet of pipe, a couple of elbows and the mix valve between it and the pump.

So the larger pipe at the rear of the photo that is connected to the hot output of the water heater continues to the right as well as turning towards the camera on the LH side -- OK. If it's not connected to the domestic hot water, where do those two large diameter (looks like at least 1-1/4", quite likely 1-1/2") go after they leave the frame?


thanks~

Bob Gagnon plumbing and heating

Can you tell what the loop lengths are by the markings on the pex piping loops?

Thanks, Bob Gagnon

Firecontrol933

Have you tried isolating the loops down to just one at a time and see if this improves the delta T for each? This would give you a hint if flow through the valve is the main and/or only issue.

nevele

I'm curious about how the heat is controlled. You say its one room so does one temp sensor control all five zones at once ?Does it control by starting and stopping the circ pump because I don't see any valves on the loops. If so when there is a call for heat the thermostatic valve would open to keep the temp of the water up and the cooler water from the zones would be coming back and this could take quite a while to balance out .By that time the temp in the room might be at setpoint. I'm no expert but that seems to be a lot of tubing (1500 ft and elbows) so I'm not really surprised that it loses a lot of its heat in the first part of the loop. thanks

LazyDevil

I think the high delta T is from trapped air. The radiant loop appears to never run past the air removal system.

If this system is not connected to the potable system, where do the other pipes go?