Constant circulating radiant heat retrofit. Help?

BrandonS · January 2021

Warning: Potentially unreasonable homeowner requesting unicorn system

I'm remodeling a home for my family in SE Wyoming. The house currently uses two furnaces. For aesthetic reasons alone I wish to retrofit with radiant heat. Two layers of subfloor I'm not interested in grinding nails for plates underneath or adding an additional layer of subfloor with plates on top. One exception is a N facing 'sunroom' with 420sq ft of glass and a load close to 12,000 BTU/H. That floor is being raised to match first floor height, and I can do in-floor with plates for that portion. I'm open to radiant walls or ceilings. The walls and ceilings are already open because the home is undergoing an energy retrofit as well. My greatest challenge thus far is finding a designer who can help me spec a true constant circulating system. I've come to this understanding because I prefer TRV control, but without radiators. I wish to proceed with the retrofit using TRVs, Danfoss FHV, Oventrop Unibox, or whatever is available in the form of non-electric control. I also prefer the mod-con boiler provide DWH, likely in the form of indirect tank. Or reverse indirect?

Heat loss calc? Yes I KNOW I need one! I haven't had one done because ideally I would get the manual J and design done by the same person. I've tried a couple of places and they are competent, but disagreeable with the premise of constant circulation, or perhaps my insistence of true mechanical control. I crunched numbers myself since I know my glass, wall, ceiling and floor u values. Just on u values I'm near 30,000 BTU/H at -1 design temp. I get hung up on infiltration loss. But I ran 70 (Delta T) x .015 (instead of .018, I used a Denver figure since I'm close to Denver in elevation) x 30,000 (cubic feet of home) x .15 (Anticipated blower door of 3 ACH50 divided by 20 as suggested) for a figure of 4725 BTU/H. So total load at design temp of around 36,000 BTU/H. I'm not going to design a system off of my napkin math, but it gives me confidence that heating is attainable at lower supply temps. Initially I don't think I'll need water hotter than the DHW needs.

In a nutshell, I'd like a true constant circulating system with modcon boiler and DHW integrated somehow. As the homeowner I will see the energy retrofit to completion and I believe we are doing a good job with that portion. I have a plumber who can install the system if it is specified. But on my own I'm not getting very far. Am I whizzing in the wind with my wish for constant circulation?

Thanks
Brandon

Paul Pollets · January 2021

Why don't you find Mark Eatherton or a local wholesaler who reps the Uponor brand. They'd be able to provide a radiant specific heatloss. Having a plumber install with little or no hydronic background, may have issues when it comes to programming the unit, not to mention the wiring. Viessmann makes the better mod-cons with constant circulation built into the control. They also make DHW indirect tanks.

epmiller · January 2021

Look into the Ultra-Fin system if you want something to avoid grinding nails. You may have to overdo the fin count to do what you want but they work if done correctly. I just did one to avoid lots of nails, a bit pricey for what they are but it sure beats plates in a tight old basement.

If you want constant circulation you are going to be fiddling with the system after installation. My circulator is running 90+% of the time but I have thermostats on the zones. Balancing them would be interesting, and then the wind direction changes. Just DON’T set it back and expect it to recover temp in any timely manner.

As to domestic hot water, an indirect fired WH is what I recommend. I’m not a big fan of instantaneous water heaters unless your water is naturally soft.

BrandonS · January 2021

Good afternoon,

I appreciate the responses. I actually have reached out to Mark E and he was very helpful. He suggested two companies to assist with the design, with one being Warmboard. I haven't reached out to Warmboard because I don't think I can afford their system albeit superior. The second company I reached out and sent plans, I have not yet heard back which is understandable. I got the impression that what I was asking for was unlikely with the desired method of control. I need to be careful because everyone I have spoken with has been helpful and competent. I've worked with Uponor before on DHW supply designs I could reach out to them. I've read their CDAM to get details on wall and ceiling scenarios with Quik-Trak as well. I could get everything from them but I don't think they could spec the preferred method of control.

Ultra-fin could be a good option. The main floor is 2350 sq ft that's why the hesitation with nail grinding or going over top. The sunroom is an additional main 350 sq ft, then there's a 1000 sq/ft basement. Their output charts reflect hardwood flooring over subfloor which matches my double subfloor currently, I intend on vinyl plank flooring on top. The outputs are low but I don't need much. Insulation and spacing with Ultra-fin is critical but I feel I could do it properly as I'm dialed in with the rest of the energy upgrades.

Thank you,

hot_rod · January 2021

If your design involves multiple temperatures a true constant circulation gets more complicated. A few ways to pipe constant circulation, a proper load and design with a well adjusted outdoor reset logic. In theory this would start up in the fall and modulate all heating season, I’d call it near constant circ. Or loop everything together as one zone, run that circ constantly, inject heat energy into the loop. A 4 way mix valve, injection mixing, pulsing a two way valve, a few options. Goggle some older Siegenthaler articles with constant circulation in the search ,for piping drawings. Some early tekmar application drawings, or Viessmann training materials Steve Minnich may be interested in this design challenge

hot_rod · January 2021

https://www.pmmag.com/articles/88410-zoning-with-constant-circulation-br-john-siegenthaler

BrandonS · January 2021

I can do underfloor with staple up plates underneath. Looked at it again this weekend the nails aren't as bad as I thought. We've been sistering the roof rafters and the roof nails have been a nightmare guess I thought the subfloor would be the same.

If it's designed*edit* as one zone with emitters sized appropriately, could it work like the picture? I like the HTP Phoenix LD. My understanding is not the greatest but I thought if it can work with radiators/trvs why not site-fabbed emitters with TRV/FHV. The picture was copied and edited from this document:
http://www.duluthenergydesign.com/Content/Documents/GeneralInfo/PresentationMaterials/2013/Day1/hydronics-siegenthaler.pdf

Does a Taco RMB or X-pump block connected to the auxiliary taps of the HTP Phoenix LD make sense or help at all with the constant circ premise? Can they be set to pressure regulate?

hot_rod · January 2021

Not sure what you mean by looped together? You can put maybe 3 panel rads on one loop, you have a bit of temperature drop across each so the last on the loop would be much lower output.
Use an H valve with adjustable by pass when you have multiple rads.

The manifold system you show is one of the best way to pipe rads if you want individual control.

You only need a mixing block if you are need two temperatures, more than 10- 15° apart. Do you?

The begining should be the load calc, after then load calc you look at the type of emitters and the SWT they require. I think you could maybe run the floor radiant and panel rads at one temperature if you play with the design.
So then the Phoenix runs on ODR and you pretty much have a constant circulation without a complicated piping.

I don't know that the Taco or Viega mix blocks are available with ECM, delta p circulators? It would be a nice option.

Constant circulating radiant heat retrofit. Help?

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