Hi-Temp + Low Temp hydronic heating...


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Old 03-28-10, 07:06 AM
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Hi-Temp + Low Temp hydronic heating...

Hi all,

Apologies in advance for the really long post.

Let me preface this question by stating that my general contractor went AWOL so I'm finishing up a major project doing what I can myself and contracting out what I can't. Anyhow...

The house is a 3-level structure with an in-law apartment on the ground floor.

- The ground level has PEX in the new concrete slab, 6 loops forming 3 zones.

- The main floor (second floor) has a new UltraFin installation with 3 loops in 3 zones. The PEX is run perpendicular through the joists (rather than along the joist bays as in traditional underfloor setup).

My understanding is that the ground floor, in-slab installation requires lower water temps (~140 F). The main floor, thru-joist UltraFin setup was designed for higher water temps (180 F).

I envision the ground floor heating will run year round, even if only to provide a slightly warmed floor, as it is essentially subterranean with no direct sunlight. I believe we won't use the UltraFin heating on the main floor except for the coldest winter months in the temperate SF Bay Area climate.

Soooo...

I'm wondering how difficult it is to run these two different temperature zones off of one boiler. There were two plumbers involved in the project prior to my general disappearing, and both thought the TriangleTube Prestige 110 was the right unit for the job, but one expressed uncertainty over this differential.

I'm inclined to attempt this installation myself (researching the Prestige Excellence w/ built-in DHW tank, so that I can quickly get the domestic hot water up and running and take my time with the external plumbing). But due to my troubles with the general, I don't want to hire his plumbers (one, who I trusted, has a close friendship with the GC; the second plumber had his own contractual problems with the GC and performed sloppy work).

Is it mainly a matter of operating efficiency? I imagine heating water to 180 just to cool it back down to 140 is wasted energy. Is there another way of doing this? Can I easily set the boiler to run at 180 in the coldest winter months when the upper level heating will be used, but turn it back down to 140 during the remainder of the year, without having to re-balance or otherwise mess with the mixing devices (which I know nothing about yet)?

Thanks in advance!
 
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Old 03-28-10, 09:21 AM
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For hot water, get an indirect tank. The built-in coils are the worst way to make hot water.

I doubt you will run that in floor heat all year round. You probably won't need anything near 140 degree water for most of the year anyway. You also probably won't need 180 for the baseboard that you have. It all depends on your heat loss and amount of radiation.

You can definitely set up the two zones with different water temps. It's beyond my knowledge on the exact way to do that so I will leave it for the guys that know much more than I do to explain.
 
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Old 03-29-10, 12:41 AM
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Originally Posted by drooplug View Post

For hot water, get an indirect tank. The built-in coils are the worst way to make hot water.
I'm not following you -- I thought the tank in the Prestige Excellence was no different that a standalone indirect water heater, just built in?

We're assuming we'll be running the ground level floor heat year-round because it's a finished concrete floor, and a little warmth makes it that much more livable, especially for my elderly in-laws. It's zoned such that I can run just the bed and bath if I so choose.

I don't have any baseboard heaters. However, the underfloor system I'm running on the main floor is designed for 180 water.
 
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Old 03-29-10, 05:25 AM
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Originally Posted by speede541 View Post
We're assuming we'll be running the ground level floor heat year-round because it's a finished concrete floor, and a little warmth makes it that much more livable, especially for my elderly in-laws. It's zoned such that I can run just the bed and bath if I so choose.
Dont forget that adding BTUs to your floor is only required when you loose some BTUs. Since this is a new structure, I would assume the glass and doors, as well as the perimeter contruction is all up to current (low loss) code. Then you have another whole story or two above it.
That space is going to haVe fairly low BTU requirements, and your floor is not going to be all warm and cozy.

Too bad we cant build like the old days, and have some vent grates between the two floors, letting some of the heat escape up to the next floor (then usable up there). Privacy concerns and firecode shut that method down I guess.
 
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Old 03-29-10, 07:10 AM
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I suppose. We have an open stairwell from the new (fully insulated) basement to the old, drafty upstairs. But there's a new layer of R13 under the hydronics on the main floor. We're hoping some of that heat bleeds up to the top floor, where we'll be living -- at least until I can get around to plumbing in some baseboard heat.

So I'm thinking a Taco iSeries mixer would allow me to dial in the lower temp water for the concrete floor, and would also accommodate any output adjustments I make to the boiler (seasonally varying between 140 and 180)?
 
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Old 03-29-10, 08:41 AM
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I think that the chances that you'll need 180 degree water in the upstairs is about zero, regardless of where you are in the Bay Area! The maximum temperature that you should ever run through concrete is something on the order of 120 degrees, and if, for example, you have 12 inch spacing and reasonable flows, 100 degree water will probably get you close to 80 degree floors. (That means that warmer water will get you floors that are to warm.) If you shock the concrete repeatedly with hot water and temperature swings, you're also liable to get some cracking.

Did you - or anyone else - do a heat loss analysis on the house? If not, since you are in CA, someone must have done a Title 24 analysis to get your permit. Get those working numbers and cobble together a room-by-room heat loss and figure out what the water temperatures are going to be.

You might find, as is the case with my house that is going to have the heat turned on for the first time in about 4 weeks, that the panel floors are as good as transferring heat as the concrete, and that the water temperature requriements are the same. Without those numbers, anything is a crap shoot, and the iSeries valve might just be wasted money and more complication.

Jeff
 
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Old 03-29-10, 09:27 AM
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Rather than argue about the 2nd floor water temp, I'll refer you to the manufacturer's installation brochure. I don't know whether you're familiar with Ultrafin, but their system doesn't come in direct contact with the floor. I did run through the various heat lost and installation programs for this setup, and 180 water is what is called for with this setup.

I don't disagree with you on the concrete, and regardless of what temp I run down there, it's going to be considerably cooler than what I need for the main floor.

Edit: Oops here's the link: http://www.ultra-fin.com/Ultra-Fin%20Manual_23.pdf and there's a calculator on their website that gets into the nuts and bolts calculations.
 

Last edited by speede541; 03-29-10 at 10:06 AM.
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Old 03-29-10, 11:39 AM
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With an earlier home I dealt with this by t'ing off the hot water return just before it re-entered the boiler (where the hot water was at its lowest temperature having been round the baseboard heating) I also had a dedicated thermostat, circulator/pump and motorized valve, this set up worked perfectly for me, the pex was tied to steel re-enforcing mesh and the slab was tiled over. I never had any cracks. With the home insulated up to Passive House standard there was never a problem holding the required temperatures. T shirts and shorts were worn all year round.
 
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Old 03-29-10, 11:47 AM
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OK - My mistake. Got it.

A reasonable boiler (and I'm sure that the TT is one such animal) will allow you to set an outdoor reset curve for the supply water temperature. For your system, you'd set the curve such that the supply temperature works for the Ultrafin. You won't need to change the temperature manually once the system is running.

Then, your iSeries valve will control the temperature sent to the concrete, and that too has its own outdoor reset curve. It does this by recycling some of the return water from the concrete. So, for example, the 80 degree return water will be mixed with some amount of 140 degree boiler water to create the 95 degree supply water for the next go round.

One problem that you might have - and this is a problem that I had to work around with my iSeries valve - is that since the valve will control all of the water flowing to the concrete, it strictly regulates the amount of heat that flows in those loops. As a result, when your boiler modulates down to it's lowest setting - say, 20K BTU - but the concrete loop is only calling for 4K btu on the warm days when you are only "keeping the concrete warm" the valve will not let that heat into the concrete, period. As a result, that heat will stay in the boiler loop and you could have a severe short cycling problem. The more that you adjust the concrete water temperature down, the more severe the problem will be - does that make sense?

If this is your setup, you'll need to figure out how to "not turn the iSeries valve down all of the way" during warm weather when you still want some heat into the concrete. Then, you'll need to find a thermostat that can maintain a floor temperature with some PID logic, I believe, but do so with longer runtimes. That is, the thermostat and the valve will need to work together so that the your 4K of heat is delivered in 12 minutes, and then the boiler is off during the remaining 48 minutes of each hour.

In fact, if you have a sophisticated thermostat, rather than using an iSeries valve, you might very well be able to get away with a dumb valve set at, for example, 120 degrees. Then, your concrete water temperature would max out at 120 degrees, probably acceptable, your boiler could generate 120 degree water, and the thermostat would control the calls for heat. The key to making any of this work is going to be the thermostat.

Or, you could install a buffer tank in the concrete loop, or in the system loop, but that would take some engineering.

I am operating my system off of solar tanks, so I really had to make this choice. In the end, I chose the iSeries ODR valve because I have both large solar tanks and a small buffer tank, and it fit nicely into the scheme. Off the top of my head, in your case, I might try to engineer a fixed valve first, to see if I could make that work with the water flows.

Jeff
 
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Old 03-29-10, 03:44 PM
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I see the problem. I've got about 1200 feet of floor to keep warm, so hopefully that won't be an insurmountable issue. I see in the iSeries instructions I can use some sort of a step-down procedure to drop the minimum temp another 15 degrees.

I guess what I'm really hoping / assuming is that I can get the boiler and water heater up and running, then doink around with this valving at my leisure. Though I definitely need to get some more thermostat wire run to all the other rooms before I close up the walls.

Early in the project, we discussed running the concrete slab off a second water heater instead of a boiler, but nixed the idea for a reason I don't recall. I'm wondering if I used a Prestige Excellence but put its built-in 14 gallon tank to use for the concrete slab, then used a 40 gallon indirect for DHW and the boiler for the UltraFins and eventual baseboard heating, if that might be a viable option or just a waste of money and effort?

Looking forward to year-round shorts weather. But that's not that unusual 'round here.
 
 

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