Solar & radiant floor

Mike Dunn

It is for both depending on the need at the time. One thing I forgot to mention is that the electric boiler and the electric water heater are both on "off peak" power rates and can be shut off during peak times. Knowing this would you setup the piping or controls differently

Mike

Wayco Wayne_2

I am working on

a radiant floor job where the hot water plant is provided by a solar system. I have the responibilty from the tubing to the manifold and that's all. However, I have been looking in on the heating plant as it is installed and have a question and concern. The solar installer has no mixing device on the RF loop. On sunny days I can see the temp of the water being higher than design. (110 slab RF) What problems could this give the system? Am I just a worry wart or should I just cool my heels? WW

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Bob Gagnon plumbing and heating

I would use a mixing valve

How big is the tank, how much solar collection does he have, and what type of radiant floor system and how many sq. ft.?

Thanks, Bob Gagnon

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Mad Dog_2

Can you post some pics or atleast a sketch????

As you know, solar hw system temps can get VERY high. You have to be careful where the pex ends and the higher temp piping takes over. I am always very careful and leery when the project is split up like that...because when there is a problem......you know. Mad Dog

Wayco Wayne_2

The RF slab is for a pool house

and is rated at 21000 btuh @ design temps. The heating plant has a 100 gallon tank wt upper and lower HX's. The system is also heating the pool and a domestic HW tank. The pool can also be used to shed heat. I'll try and draw what he is doing and attach it later. WW

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Wayco Wayne_2

Here's a

quickie drawing. WW

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Wayco Wayne_2

Bump

What could happen if really hot water goes through a radiant floor pex in slab??

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Unknown

wayco,

we questioned using a boiler like this (looks like you're using it for boost).

won't it freak out if water coming in is a hair hotter than water leaving?

I'm not saying it would, we were just concerned about it when we considered that kind of a setup.

as for your question, what would happen if the water exceeded your pex temperature rating? I would at least demand that they make sure that cannot happen.

Derheatmeister

Burst!

I have seen a solar direct system that most likely lost power and was "superheated" as the power was restored...

One of the pex supply lines had expanded into twice its normal size just to burst after that. I would "restrict the temp".

Wayco Wayne_2

My concerns

Thanks for the feedback. I may go as far as to offer to put in a thermostatic mixing valve just to protect my pex. Rob, if the return water to the boiler is warmer than the set point of the boiler, the boiler just won't fire up. I don't see a problem there. Thanks for the feedback guys. WW

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Unknown

yes, our concern was simply if the sensor read, say, 100 coming in and 99 going out, it might cause a fault in the boiler controller. the weil-mclain Ultra, for example, would lock out if that happened, if I'm not mistaken, which probably means the prestige solo would too since they use the same controller.

5 soft lockouts would then result in a hard lockout.

Or... maybe I'm a crazy head!

Wayco Wayne_2

I don't think you're acrazy head.

That sounds like a totally possible scenario. Who says the return and supply sensor are not a degree or two off. Depending on which way they might be off. If the supply is a little low, or the return is a little high it could happen. I'll alert the solar guy. He just went to triangle tube school on the Prestige in Blackwood, NJ so he may even know about it. I heard from the Ultra expert they had a problem with the flu sensor too. WW

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Bob Gagnon plumbing and heating

High Temps Vs Low Temps

I would try to set it up to take advantage of the efficiency of harvesting lower temp solar btu's. If your going to keep that tank heated by the boiler at, say 160 degrees, your collectors won't collect much heat waiting around for the collectors to make 165 degree water. Radiant floors and pools make excellent solar delivery systems because they use lower water temps and 95 degree water is a lot easier, and efficient, to make than 165 degree water. I would separate the systems and make the radiant floor or pool supplemental so you can run your tank at the lowest temperature possible so you can harvest the most btu's. A lot of people pipe solar systems like your solar installer, but I think it could be a lot better. We have to work to improve these systems and I think there is a lot of room for improvement.

One question I have is a BTU at low temperatures the same value as BTU'S at higher temps? For example if we get a 10 degree delta tee at 95 up to 105 degrees, are those BTU'S the same value as a high temperature delta tee of 10 degrees at 165 to 175 degree temperatures? It's a lot easier to make heat at the lower temps, but 10 degrees is 10 degrees, right?

Thanks, Bob Gagnon

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Rich L.

BTU's

Absoutly Bob, A btu is a btu (the amount of energy required to raise 1 pound of water 1 degree F). If we were talking about 1 lb of water it would require the same amount of energy to raise it from 95 to 105 as it would take to go from 165 to 175 degrees, 10 BTU's. This applies to sensible heat only.

That said with heat transfer being more efficient the greater the delta T than the lower temps would stand to be much more efficient.

BTW I really like your website Bob!

Best Regards, Rich L

Unknown

that's a mod/con, not a regular boiler. with a reset curve, return temps to the tank could be quite low indeed (depends on the radiant water temp requirements). technically still providing some heat to the tank, but definitely not high temperatures.

so not 100% purely ideal, but quite possibly it's not a bad idea at all... I've done an awful lot of systems where the maximum return water to the tank would be 95 degrees in that setup.

I do like either/or systems though and not maintaining tank temps for domestic (using on demands instead).

Wayco Wayne_2

Yeah

I'm not sure I agree with how it is set up, but I just have to protect the RF at this junction. It's fun observing and working on my own ideas. I think the highest temp for the boiler is 110 so is won't heat the top of the solar tank too much if it is cold out. However when it kicks into high temp for shower water from the indirect it will heat up the top of the solar tank a lot. Hmmmmm. This is a puzzle. What is the best way to do this? Where is my Peter Biondi book? WW

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Unknown

It's tricky with two tanks. you're right though, DHW demands are likely to dump quite a bit of heat into the solar tank. DHW return should bypass the tank entirely. a separate recirc loop between the two tanks with a dT controller could prevent DHW maintenance demands, too... letting the solar do the job.

Mike Dunn

Solar radiant drawing

Hi everyone.

I am designing my first solar DHW with space heating job and wanted some input on my design. I am especially curious about tying in the pool HX. Control would be based on priority. DHW 1st, Radiant 2nd, and Pool 3rd.

Mike

Wayco Wayne_2

Mike

As far as I can see your drawing makes perfect sense and is more how I would design such a set up. One question though. Is the pool HX for dumping heat or for pool heating? WW

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Wayco Wayne_2

Does anyone know

of a website for solar that has a forum like HH.com for questions and discussion?

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Bob Gagnon plumbing and heating

There is a LOT of talent

on this we site, but I would also be interested in another solar specific site too.

To protect your radiant system I think just adding a thermostatic mixing valve would limit the water temps going into the radiant floor system.

To make the system more efficient I would separate the systems. You might see low returns temps when it isn't that cold outside, but the return temps will increase as it gets colder outside. An when it is cold outside, that's when it is harder and harder to make higher temperature water with solar. Also this system seems to be either all or nothing from the solar, like most are. There will be lots of days when solar could provide 25% or 50% of your needs, and with a separate system you could use that solar heat, and keep you tank at the lowest possible temperature, and make it more efficient and easiest to harvest those low temp BTU'S, at the same time your boiler and other radiant floor system is running. You could harvest and use a percentage of your heating needs from solar every sunny day throughout the winter and not just in the shoulder season.

Thanks, Bob Gagnon

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hot_rod

Some large solar \"heating\" arrays

are installed at steep, maybe 75 degree angles to leverage winter sun but lessen the summer overheat potential.

All of the answers you need will show up in the solar design data if you run the design through RET screen (a freebie) t-sol or a few of the other softwares out there.

Its hard to answer your questions without a bit, maybe a lot more data.

I'd agree that you would probably be wise to add a temperature mixing and limiting device. a listed 3 way thermostatic may be a simple method.

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Wayco Wayne_2

Hor Rod

You mention some software freebies. Could you provide a link so I can find them. Thanx. WW

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Wayco Wayne_2

RET Screen

I found it by googling. http://www.uneptie.org/energy/tools/rets/index.htm

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Kevin_in_Denver_2

Another Solar Forum

Try
http://www.greenbuildingtalk.com/Forums/tabid/53/view/topics/forumid/15/Default.aspx

Unknown

note that almost all solar programs I've seen out there will generate numbers that, shall we say, don't necessarily reflect reality on the roof.

hot_rod

reality on the roof

is all but impossible to nail down. Ambient temperature, wind, dust or smog in the air, mounting position, etc will all have an effect on the panel performance.

Like a heat load calc, I suppose, there may be a point in time where the panel matches the stated output.

I think the ASHRAE standard and SRCC listing criteria comes fairly close to determining some accurate data.

Body Cote uses indoor testing conditions, while the lab in Florida tests panels outside. In either case it is hard to create ideal actual conditions for all areas where panels may be installed.

Regardless, if you ballpark 25- 30,000 BTU per day for a 4X8 flat panel you're probably in the ballpark for designs, according to one panel manufacture.

You can crunch numbers until you are blue in the face and never come to an exact output considering all the variables that the installer builds into the installation, and the conditions mother nature will throw at that heat exchanger on the roof.

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