Sanity check on radiant system install

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  #1  
Old 06-27-15, 08:06 AM
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Sanity check on radiant system install

Hi,

So I'm in the process of remodeling my house (including heavily insulating and air-sealing) and changing the hydronic system over from baseboards to radiant floor heating. The boiler is an older Slant-fin 150K. My plan is run the boiler loop through an expansion tank, air eliminator, 4-way motorized valve and then through three zones with each zone having a med-head circulator pump. I had a few questions:

-Does the boiler loop need a separate circulator pump? My "Modern Hydronic Heating" textbook suggests it doesn't. The existing baseboard setup has the circulator pump (a Taco 007) on the return side right up against the boiler. Should I move that pump to the supply side? Remove it? Leave it in place and dormant? Or hook it up to the control system so the zoning circulator and the boiler loop circulator(s) are running at the same time?

-The 4-way motorized valve from taco seems like a reasonable way to get outdoor reset and boiler temperature protection. Their seem to be a dozen ways to do this. If someone can confirm, this makes sense in my case, I would appreciate it. The boiler seems to have a few more years left and at some point in the future I plan to switch to a high efficiency boiler/water heater that doesn't need a minimum temperature.

-After purchasing a bunch of the parts, I stumbled on the idea of the injection mixing block like the Taco RMB-1. Since I would have a restocking fee, my current planned setup would probably cost about the same as injection mixing block. Is it really that much more efficient to go with the RMB-1 in my small (1600 s.f. heated space) residential system? Or would the electricity and maintenance costs of either system likely be of minimal difference over the next decade?

Thanks for any help! Although I have a bunch of plumbing and remodeling experience, hydronic systems are new to me. I've done a heating load calc and have the tube and plate systems figured out. This is the last bit.
 
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Old 06-27-15, 08:36 AM
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I'm not an HVAC pro and cannot help on your configuration, but you seem to be getting ahead of yourself.
1. What is your objective, like reducing energy costs, or purely comfort?
2. With a 150K boiler and a 1,600 ft² heated space it sounds like the house needs more improvement before you decide on a heating system change.
3. If you do a great job of insulating and air sealing, a radiant system might be a poor match for heating. By the time the floors get warm the house will be on its way to being too hot, overshoot.
4. Response time for radiant is very slow, but the pros will discuss that if it is an issue.

Here is a link, if you haven't seen it, from Efficiency Vermont, on air sealing.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

There are heat loss calculators that you should be using to help decide where your energy efficiency efforts should be targeted.

Bud
 
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Old 06-27-15, 09:56 AM
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Thanks for the reply!

1) The main goals are comfort and as part as a larger energy efficiency strategy. I've lived in houses with radiant and like the experience. I also like that radiant can be run with lower water temperatures. I won't deny that one of my motivations is that I like the idea of radiant floors and I am OK with paying a premium for that.

2) After the remodel, insulation and air-sealing will be above modern code (R25 walls and R60 attic and below 0.35 ACH). Boiler was sized for house that was entirely uninsulated, with massive air leakage in a region with a winter design temp of -7 degrees F. My heating load calc for the remodeled house shows a total heat loss of about 50K BTU at design temp vs 125K BTU for the original.

3) 4) You are definitely right above the limitations of hydronic radiant. We are taking some steps to help with comfort such as using outdoor reset, an above-floor tube and plate system and smart thermostats.
 
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Old 06-27-15, 10:18 AM
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I do understand how a project can be fun and it sounds like you are doing your homework on how a radiant system will work.

You reference the 0.35ACH, and I hate that number. It was created to allow the weatherization assistance programs (WAP) to get in and out without having to do anything extra to provide fresh air. Yes, it is a threshold, but it is not a stop line. I've seen homes where they air sealed only what they could easily reach from the attic opening because the rest was hard to reach and might put them below the 0.35 where they would have to activate an exhaust fan.

In an existing home, seal everything you can as tight as possible, especially older homes. You can then have a blower door test done, or monitor your relative humidity. A home that is too tight will have 50% or greater RH and the windows will probably sweat. If you engineer an air exchange system from the start you just activate it at the desired rate. But every home will have a different level and your home, based upon people and activities may be just fine down to 0.2ACH and benefit from the reduced air leakage. As I sit here typing with my back door wide open, there are many days when fresh air is plentiful, especially up here in the north east.

Bud
 
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Old 06-27-15, 10:42 AM
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I definitely agree with you - 'Seal tight and ventilate right'! I've been on both sides of that - sometimes pushing for more air sealing on certain jobs and sometimes pushing against the myopic desire of weatherization programs to spend thousands of dollars in man hours chasing the last a few less CFM on the blower door number.

But I'm very curious if anyone has thoughts on my original questions about the radiant system and the setup of the mixing setup on hydronic boiler and distribution loops. =)
 
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Old 06-27-15, 10:58 AM
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The forum is very slow currently and I attribute that to summer. Between work and play, the forum is difficult to get to at times. Be patient.
Bud
 
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Old 06-27-15, 01:00 PM
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Just to add to it. This is the plan I am proposing. Any suggestions appreciated!

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Old 06-28-15, 08:55 AM
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My typical comment when someone proposes installing radiant in place of baseboard is to do your homework and make sure that the radiant system can output the BTUH you need to heat the home. You seem confident that you have done that, so I won't go there...

Did that diagram come from Siggy? out of MH?

I don't think it's right...

Let's say the boiler is cold and a heat call comes in. Your 4-way valve is going to be in the position that only allows circulation on the boiler side. In other words, the left and bottom ports are open to each other, and the top and right ports are open to each other. There won't be any circulation in the boiler loop without a pump.

Do you have room for a buffer tank? I think you'll need one. That boiler is probably going to short cycle (it probably already does anyway).

Not sure that's the right location for the spirovent and expansion tank... it might be better on the supply side of the heating side of the 4-way... or, maybe air removal at BOTH places. I suppose that eventually all the air will be removed with it at that location, but it's possible that you could have air going round and round in the heating loops and not get back to the boiler.
 

Last edited by NJT; 06-29-15 at 08:06 AM.
  #9  
Old 06-29-15, 04:27 PM
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Definitely need a boiler pump....
Definitely agree with a buffer tank, and the bigger the better.
Maybe use a TT smart 80 indirect to buffer the load.

Air elimination "should" be nearest the hottest water, as this is where the air comes out of solution the easiest.
Though the secondary loop may have a higher flow rate then that of the boiler loop.
Buffer tank has the added benefit of being an air elimination tool as well.
 
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Old 06-30-15, 06:11 AM
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Thanks for the info. It definitely makes sense to me now that I need a boiler pump.

What rule of thumb do you use to size the buffer tank? I see they come in 30 gal sizes on up.
 
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Old 06-30-15, 06:46 AM
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Read here on the boiler buddy...

Boiler Buddy - Installation

I believe they are pricey as why a TT 80 was recommended...
 
  #12  
Old 06-30-15, 03:45 PM
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I use these tanks
CoolFire Buffer Tanks - Thermo Matrix

I have no idea what there dealer network is like down states side.

Heck they may even sell direct ?

They are nice tanks (all Stainless, which is overkill), and have lots of large ports.
 
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