caulculating loss in hydronic mains

Big Will

Big Will

1.5 inch mains about 250'

They wrap around the exterior of this guys house for base board heat. 2800sq foot house. The crawl space was 62deg its 45 out side. The insulation under the floor is R19. Just to make the point with the customer I wanted to show him how much he was loosing. The rest of the install is just as goofey. If I get the job I will post pics.

Brad White_185

Depends on your water temperature and flow rate.

Will, lets say you have a flow rate of 10 GPM for argument's sake.

If your water temperature enters at 180F in a 62F space, the loss by the time the pipe ends, the losses would be about 23,750 BTUH and you would lose about five degrees. This of course does not take into account the losses to the occupied space. (Without those, just WHAT is the purpose of this magnificently sized main? )

Here are losses as above but ad different water temperatures, same 10 GPM and same 62F ambient:

150F: 16,585 BTUH loss

130F: 12,090 BTUH loss

100F: 5,900 BTUH loss.

I used John Siegenthaler's Hydronic Design Studio "Pipe Heat Loss Estimator" module by the way. Credit where credit is due...

Hope this helps.

don_185

checking

Checking HDS at 14 gpm and a 180 degree watertemp with ,a
62 degree basement temps he losing about 19.202 degree for your size pipe and lenth.Leave you with a 176 starting temps.

AS you know the btu loss can change either way depending on temps.

Big Will

They are insulated. I was looking for the process mathmaticly to find the loss. SO I could do it again. The insulation is 3/4 inch with some voids. They ran the main all the way around the home and used zone valves at each base board. Then the retun follows it. So the flow is variable depending on how many zones are open. On the main line size I cant think of why they are so big. Their is alot of really off things about the system. For instance the boiler supplies domestic also but the storage tank is not insulated at all. It keeps the garage nice and warm. The boiler is a Polaris 100 kbtu.

Brad White_185

Roughly speaking

you could knock about 75 percent off the numbers I gave. The 180/150/130/100F spread I gave with 3/4" insulation would have losses of 5,300, 3,940. 3,040 and 1,700 roughly..

Because your flow varies as will your temperatures, all I can do is bracket the numbers for you.

Does not seem so bad and it underscores the notion that the first inch of insulation does most of the work!

Big Will

The thing that bothers me is that the mains are hot when only one zone is calling. I would think that a few 3/4 inch runws back to a manfold would cost about the same as a 1.5 inch main.

Brad White_185

Temperature versus Flow

It does not take much flow to bring or keep a line at temperature. (DHW recirculation systems illustrate this.)

Never mind a few 3/4" homeruns being less money, of course they would be. But if you use Pex-Al-Pex, even better. Up until now we have not been discussing your approach to this job, rather what the line losses are.

If the pipe is already there, I would keep it and work with it although one might argue the cost of tying in a pair of 1-1/2 x 3/4 tees can get up there quickly.

If you were to remove that copper main (I assume it is copper) the owner's home value would drop by half

Big Will

I let the guys keep the copper from jobs like this

kind of a perk I guess. They jumped for joy when I said we would probably be pulling out this much copper. I might not pay them for the day they will make more than I will.

Big Will

Brad white

what formula do you use to find the loss from a pipe in this situation. And thanks for the info it really helped prove the point with the customer. The household total load was only 67kbtu so the mains were almost 10% more.

Brad White_185

I used HDS

John Siegenthaler (aka "Siggy") has a program called "Hydronic Design Studio", same as Don used. The algorithms are ASHRAE-based I believe and the program saves a lot of time. (There are a good number of modules within the program, a lot of small quick tasks that are made, well, small and quick by using HDS.)

There are other tables I have but it gets down to the emissivity of the pipe and the ambient temperature. There are even some tables regarding bare pipe loss on this web site. Check out the library.

A very neat (and free!) software program I use at work, "3E Plus", available at http://www.pipeinsulation.org/ is about the best freeware I use. Great for a lot of "what-if" scenarios.

Give it a try!

Hope this helps-

Brad

Big Will

Thank you

Brad I owe you a beer. Next time your in the wine country.

Brad White_185

I go to your wine country

and I get beer?



There is a biblical reference here somewhere...

My pleasure, Will.