New radiant system questions. 1 zone + domestic hot water... same temp or 2 temp system

sallydog

1100 sf . 1/2" pexO2 in a concrete slab with 1" insulation below. 9 loops 160' , all on the same zone. i am in NC. 55000 btu boiler. can i run the floor and DHW tank the same temp or do i have to do a 2 temp system? also does anyone know where i can get a pipe diagram on the net for the system i need so i know how to set it up with the proper valves, pumps, switches etc similar to
http://www.radiantcompany.com/wp-content/uploads/opensolartie.jpg
any help/advice is appreciated. i cannot afford a prefab panel and have to do this myself

Gordy

Two temps are needed to get the most performance out of your indirect. Radiant floors will need much lower temps.

Boiler type?

Ironman

If you don't have the Polaris yet, I'd recommend that you consider a mod/con instead.

But to answer your particular question: no you can't use the temp of the indirect, it will be too hot for the slab most, if not all of the time.

A slab is high mass which means it takes a long time to heat up and a long time to cool down. It's called the flywheel effect. You need a smart control that varies the slab water temp based on outdoor reset.

sallydog

im not going with polaris, probably going slantfin and i am doing electric because i am in the boonies and its that or propane

sallydog

Ironman said:

If you don't have the Polaris yet, I'd recommend that you consider a mod/con instead.
You need a smart control that varies the slab water temp based on outdoor reset.

bob, where can i look up "smart controll for radiant"? im just finding thermostats. im assuming you mean a controll box of some sort

Ironman

Tekmar's 356 or Taco iSeries valve.

sallydog

Ironman said:

Tekmar's 356 or Taco iSeries valve.

Thank you. what temps are best for concrete floor and DHW?

Ironman

TYPICALLY, we don't wanna see concrete water temp go above 110*. That's NOT saying that's the water temp that you should use.

As I stated before, you need a smart control that will VARY the water temp based upon outdoor temp. It's called outdoor reset. You don't want the surface of the floor to get above 84* in a living area (except bathrooms).

In order to know what supply water temp is needed at design temperature, proper calculations are necessary. There's no pat answer. These calculations involve a heat loss for the structure; the amount of insulation; the size, length and spacing of the tubing; the square footage and thickness of the slab; the flow rate; and the R value of the floor covering.

From these the SWT is determined and the outdoor reset curve is plotted in the control.

There's a WHOLE lot more to doing radiant than just laying pipe in the floor. If PROPER design is not done and followed, then your gonna be another one that joins the chorus railing on radiant when the problem wasn't the radiant floor but the lack of proper design and installation.

Jean-David Beyer

"TYPICALLY, we don't wanna see concrete water temp go above 110*. That's NOT saying that's the water temp that you should use." -- Ironman.

I have a radiant slab downstairs and an indirect-fired hot water heater. On warm days like today (outside temperatures above 50F), I put 80F water in the slab if the thermostat calls for heat. And that is enough.

Design day temperature is 14F around here. On such a day, I put 116F water into the slab. I rarely see the outside temperature go below 9F, but last year it went down to about 2F and I had to set the reset curve to go up to 130F if it gets down to 0F outside. The floor temperature is less than the water supply temperature, but I do not remember what it got to that day.

My indirect is supplied with 190F water when it calls for heat.

I also have baseboard upstairs with oversized baseboard units. The house originally had 3 feet of baseboard in each of two rooms, and they were always too cold. I now have 14 feet in each of the two rooms. I supply 120F to 150F water to these, depending on outside temperature.

The radiant zone takes 24 to 48 hours to recover from a temperature change, so I can forget about setbacks there. The baseboard zone does not recover from setbacks very well either because the outdoor reset delivers just enough heat to maintain the desired temperature, but not enough to recover. The controller does have a boost feature, and that helps somewhat, but I just run upstairs at a constant 68F all the time, and downstairs at 69F.

So I actually have three temperatures from my boiler (one temperature at a time) in a very small (1150 square foot) Cape Cod type house in New Jersey. Clever controller can manage that with one extra relay.

sallydog

Guys, thanks for taking the time to explain all that. it helps me alot. do you know where i could get a piping diagram of a system like i need. 1 zone for heat and a second zone for DHW? since i am not a boiler guy i dont know which valve types go where.

Ironman

You need more than a diagram, you need proper design based upon an accurate heat loss calculation. THAT is the foundation for everything.

You can go to SlantFin and download their free heat loss app. If you put the correct info in, you'll get the correct calculation. Start there.

sallydog

something like this one i found for an outdoor furnace

ratio

There is a treasure of information at Caleffi, in their Idronics magazine. They show piping layouts, and explain why one is preferred to the other, as well as the calculations necessary to size it. You would be well served to study them.

sallydog

ratio said:

There is a treasure of information at Caleffi, in their Idronics magazine. They show piping layouts, and explain why one is preferred to the other, as well as the calculations necessary to size it. You would be well served to study them.

thank you

ratio

You're welcome!

Please don't disregard the "study" I mentioned. Each system is a snowflake, no two are alike. The generic piping layouts are a starting point, & need to be tuned to your particular installation for the sake of efficiency & safety. However, with patience (& pictures!) the fine people here can give you advice & suggestions that will rival an expensive engineering survey.

Ironman

That Central boiler diagram is about worthless. It shows a radiant floor connected directly to an unpressurized outdoor wood boiler without proper means to control slab water temperature.

Please heed what I'm trying to relate to you: you don't need a diagram at this point. You need to know what the actual heat loss of the structure is before doing anything else. This is the starting point, not a diagram. From this, everything else is determined: the output of the floor; the pipe sizing and layout; the circulator size; the controls to be employed, the size and type of the boiler. If solar is used, how many panels and what percentage they can contribute to domestic and space heating. Everything designed into the system is based upon a heat loss calculation.

As Ratio said, no two systems are exactly alike. There's no generic, simplified way to approach this if you want the system to turn out right.

If you'll do the heat loss calc and post the numbers here, then we can begin to give you some specific design criteria.

hot_rod

Ironman said:

That Central boiler diagram is about worthless. It shows a radiant floor connected directly to an unpressurized outdoor wood boiler without proper means to control slab water temperature.

Please heed what I'm trying to relate to you: you don't need a diagram at this point. You need to know what the actual heat loss of the structure is before doing anything else. This is the starting point, not a diagram. From this, everything else is determined: the output of the floor; the pipe sizing and layout; the circulator size; the controls to be employed, the size and type of the boiler. If solar is used, how many panels and what percentage they can contribute to domestic and space heating. Everything designed into the system is based upon a heat loss calculation.

As Ratio said, no two systems are exactly alike. There's no generic, simplified way to approach this if you want the system to turn out right.

If you'll do the heat loss calc and post the numbers here, then we can begin to give you some specific design criteria.</blockquot

It does show a 3 way thermostatic mixer, for the radiant, and what is that device under the water heater, is that some sort of HX to isolate the open boiler from the house side?

Ironman

Hot Rod,
Yes, I saw the thermostatic mixing valve, but I'd hardly consider that the correct mixing device for a slab.

The pex is non barrier. The radiant side shows no fill valve, expansion tank or relief valve. So, I can't see how it could be pressurized. I don't know what the device is in the lines coming from the ODWB, but since there's no circ between it and the side arm, I think we would be safe assuming it's not a heat exchanger that's isolating the ODWB from the house. That means the drawing is showing the radiant floor directly connected to the unpressurized ODWB.

Unless you see something that I'm missing, that makes the drawing useless.

This is not the first time I've seen that drawing, but my opinion of it has always been the same.

ratio

That thing in the lines from the ODWB seems to be some kind of thermostatic valve. The notes call for a pump at the ODWB, & the thing beside the water heater is a heat exchanger, it seems the intent of the water heater is supplemental heat? No sign of make up water to the water heater, nor provisions for any kind of thermal expansion. At least the T&P valve is shown, that may keep it from exploding.

Ironman

ratio, that's a side arm heat exchanger so the ODWB can heat the domestic water.

ratio

Is it? I didn't see any obvious attachments to the domestic water indicated. At first, I thought those things at the inlet & outlet were air vents, but maybe they're a side view of a ball style boiler valve?