TRVs on a Monoflo system?

Steamhead

Anyone done this? I'm wondering how TRVs shutting down radiators will affect the flow in the loop. Customer is looking at doing hot-water heat with panel rads to replace a substandard forced-air system, and a Monoflo loop would be a perfect fit- less piping than PEX home-runs and a neater result. House will have 11 radiators, with maybe 6 having TRVs. Thanks in advance!

EdTheHeaterMan

DON’T DO IT

EdTheHeaterMan

The pressure drop thru the radiator is part of the mechanics of the design. Adding TRVs will add pressure drop and those rads won’t get any heat

TRVs will work on reverse return, direct return and home run. Not on diverted tee systems. On page 20 of this text you will find a discussion on your query

http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf

mattmia2

Isn't there a radiator valve for European style radiators with a built in adjustable bypass that lets you put the radiators in a loop and put a TRV on each radiator?

Steamhead

That's what I thought, but wanted to confirm it. Thanks!

hot_rod

Never done one myself, I think it is doable. You could TRV a group of panel radiators in one room for example, and use a diverting H valve as @mattmia2 mentioned.

Chapter 11 in Modern Hydronics Heating shows examples, similar to this PM Engineering article. Find the textbook on Amazon if you don't have one

Pretty math intensive designing a proper one-pipe system. i'd like to see one done from scratch, you're the man to do it

https://www.pmengineer.com/articles/85479-a-simulation-model-for-diverter-tee-systems

HVACNUT

If you were dealing with an existing mono flo system, I would say go for it. I'm not a layout or design guy by any means, but aren't there better alternatives if you're starting from scratch?
This will be a condensing boiler, or no?

hot_rod

With ECM circulator technology, the circulator being able to constantly adjust, I think it would be fun to design a single pipe, constant circulation system. I'd bet it would be extremely quiet, comfortable and efficient.

Steamhead

Interesting- but this may not be the job to try it. This customer wants a system that is comfortable, simple, reliable and reasonably efficient.

That rules out mod-con boilers and fancy diverter valves as far as I'm concerned. From experience, I agree with @The Steam Whisperer and others that today's mod-cons are of questionable value, since they break down more frequently, don't last as long and require more regular maintenance than cast-iron boilers do.

Then there's the parts situation. The mod-con industry has not made any attempt at standardization. During the 1930s, the oil burner industry went through the same thing. I've read several articles from that time that advised customers to make sure their burners were built from standardized parts (motors, fuel units etc.). This way, it would be far easier to get them running on the proverbial 5-degree night. And today, with the exception of Riello, one can repair any common oil-burner problem using standard parts carried on the truck (I have the Riello kit as well), and there's no waiting 1-2 weeks for a part to come in. Same with most standard gas boilers. This is to the customer's advantage.

So yeah- keep it simple on this job.

hot_rod

Panel rads need some sort of valve to connect into them. usually a H valve.
The single pipe, or diverter style H valve has another valve in the middle. It allows you to balance how much flow goes into each radiator.

In a room requiring multiple radiators, a single TRV, then adjust flow to each rad to balance. It saves cost by not needing a TRV on each panel.

EBEBRATT-Ed

@EdTheHeaterMan

is right . I have designed some small one pipe systems. Some flow goes through the radiation and some through the loop. Increasing the pressure drop by shutting the rads off with TRVs will increase the system pressure drop

hot_rod

EBEBRATT-Ed said:

@EdTheHeaterMan

is right . I have designed some small one pipe systems. Some flow goes through the radiation and some through the loop. Increasing the pressure drop by shutting the rads off with TRVs will increase the system pressure drop

Did any of the systems get installed @ EBEBRATT-Ed? Do they work well? Noisy? What type of circulator did they require?

I'm curious now with more "smart" component in hydronics how feasible this would be. In the past, pumping power, related to pressure drop, seemed to be the biggest concern. With todays circulators a 50- 80% reduction in power consumption might be a reason to reconsider a simple one pipe system.

TRVs are an under utilized hydronic component in North America. I think they are one of the best and simplest temperature control mechanism.
This FW Webb piece has some additional sizing info.

PerryHolzman

Steamhead. As you know the monoflow T system is amazingly simple and works extremely well when its designed and built right. I have a cast iron baseboard monoflow T system built in the mid 1950's. The only (minor) defect is that the previous owner removed several of the baseboard sections from the kitchen to install modern kitchen cabinets (the removed sections are in the detached garage attic).

The heat in my house is constant and steady. My wife is impressed with it.

I'd say go for it - and just skip the TRV's. Do the math, ensure piping is sloped properly to prevent air binding (my entire monoflow T loop runs uphill around the basement; 1/2" per side).

Either that or run a 2 pipe system with TRV's, with several of the radiators without TRVs to ensure minimum flow.

Design radiators for 120 F or 130 F water. That way if it gets really cold (or there is a mistake in the calculations) the water can be raised to 140F and appropriately heat the house.

I second your concept of a simple heavy cast iron boiler (the heavier the better as that means the cast iron is thicker).

While I like my Vitodens 200. It has not overall paid off, and things would be far worse if I had to pay a contractor for repairs and service, instead of doing it myself.

I do like the indirect hot water heater tank a lot.

Perry

Steamhead

She definitely wants TRVs- has traveled in Europe and has used them there. I think I'll just do 2-pipe- a bit more piping but with ProPress it should go quickly.

If this were my house I'd try a Monoflo system with a few TRVs, but it's not.

EdTheHeaterMan

Good choice @Steamhead. And I agree with the TRVs. The best way to zone each radiator. You won't get any complaints about setting the temperature at 68° but the room is 71°. A big advantage when some rooms are unoccupied from time to time

JUGHNE

I too have traveled in Europe and was impressed by some things there. I understand the impression it left on her.
If she wants it, she wants it.

But, do not want to bring all of those back here.
For instance, your used TP would go in a trash can next to the WC.....that left an impression on me.
Grateful for the sanitary system we have here and biodegradable TP.

HomerJSmith

I did it and it was successful. This is how I did it.

It was a 3 story house with the modcon boiler on the bottom flr.
It was on the longest baseboard run in the house and consisted of 2 Runtal flat panels with TRVs and an added small injection in-floor loop.

The primary on the P/S boiler sys had 7 zone valves and was powered with a Grundfos 15-58. Some circuits were a lot shorter than others, something had to be done.

I changed the primary pump for a Alpha-2 and I added balancing valves on all the circuits which I set at 2 gpm. However, the longest loop was shy of my design gpm, so, I added the old 15-58 in that circuit and on speed MED could set the flow to 2 gpm.

A Mono-flo tee has an equivalency of 75' of straight pipe, I think.

The flat panel Runtals had Oventrope TRVs, as I ran them in series with the baseboard. I used one Mono-flo tee on the input of each Runtal. I used real Mono-flo tees and not diverter tees.

No matter how cold it was outside, it kept the rooms at a constant 55 degrees. (just kidding) It was a roaring sucess, in fact, I amazed myself.

I am a big believer in balancing valves and ECM pumps.

Running them in series or parallel makes a difference.

Steamhead

JUGHNE said:

I too have traveled in Europe and was impressed by some things there. I understand the impression it left on her.
If she wants it, she wants it.

But, do not want to bring all of those back here.
For instance, your used TP would go in a trash can next to the WC.....that left an impression on me.
Grateful for the sanitary system we have here and biodegradable TP.

The Lovely Naoko encountered the same thing in Shanghai, China. One would have thought Europe was more advanced than that................

Big Ed_4

Using Panel radiator with diverter valves could be an option But tricky to adjust , Go with the home run with TRV's with a EMC circulator , reverse return on the manifold , . 3/8 Pex tubing is all you need and a pleasure to run ... Add a outdoor reset , the system sings ..

dopey27177

Adding TRVs to a monoflo system is a no no.
creating a large pressure drop across the circuit will stop the flow of water to the radiator or convector where the TRV was installed.

Jake

Henry

Some 30 years ago, I transformed the only one pipe gravity 8 floor industrial building to TRV at each rad. It was the 8 floor Northern Electric. Large mains would go up to the ceiling of the top floor. Distribution was a single pipe going down. Each rad had two special TY. One diverts into the rad and the other works like a monflow back into the "downriser". I moved each rad 8 inches to install the TRV. It worked for 20 years until they made the building into condos.

jumper

Gravity can work quite well with overhead distribution as described below. Even better with separate supply & return "downrisers". Some old Toronto mansions had them. I presume that before Henry installed TRVs somebody balanced the system manually?

Henry said:

Some 30 years ago, I transformed the only one pipe gravity 8 floor industrial building to TRV at each rad. It was the 8 floor Northern Electric. Large mains would go up to the ceiling of the top floor. Distribution was a single pipe going down. Each rad had two special TY. One diverts into the rad and the other works like a monflow back into the "downriser". I moved each rad 8 inches to install the TRV. It worked for 20 years until they made the building into condos.