Help dial in DWH

digger_2

I put my Lochinvar WB-050 and 40gal Squire indirect on line this past weekend. The only glich is with the existing in floor tubing. Save that for another thread.



My question has to do with the DWH. With the boiler firing 100% on a call for DHW, I see only a 18*F rise through the boiler. The return water is coming back much hotter than the tank when it gets going. Would it heat water more efficiently if I slowed the pump down and got cooler return water? Would it heat the DWH just as fast?

BobbyG

delta t

Nice piping job ;-)

If it's firing at 100% and not ramping down, you're delivering the btu's, slowing it down won't help.  See the article below.

took me forever to find this article. In case the link doesn't work:

June 1, 2000 John Siegenthaler,P.E., "The Water's Moving Too Fast" Plumbing & Mechanical Magazine 

[url=http://www.pmmag.com/CDA/Archives/de452c49e3fc7010VgnVCM100000f932a8c0]http://www.pmmag.com/CDA/Archives/de452c49e3fc7010VgnVCM100000f932a8c0____

If link above doesn't work:  [url=http://www.pmmag.com/]http://www.pmmag.com/

search: editorial button and Waters moving too fast

L'town Radiant_2

DHW ΔT

That's a great article Bob. Good Find! .....and that's a fine looking install, Digger. I'm curious though if placing the Spirovents directly before the circulators will have any detrimental effects on the pump.

digger_2

Explanation accepted

The train of thought behind the question was about lower return temps = higher efficiency. The fire rate would eventually ramp down on call for DHW but the call is usually satisfied before the boiler reaches it's 180*F set point.



L'town, now I'm curious about the vent placement. I put 4" long nipples between the 1" B&G EASB-Jr and the pump flanges. 

Slimpickins

pump placement

It's fine to have the air eliminator on the suction side of the pump and its the preferred method if you have the fill and expansion tank at that point below the eliminator. I read somewhere, maybe a Siggy article,  to get the pump as close as possible to the air eliminator. I can't remember the reasoning beside it's the PONPC. 

BobbyG

lowest pressure + highest temp. = best air removal

Because the suction side of the pump is the very lowest pressure in the system.  Which is the best possible environment for air to "come out of solution".

The outlet side of the pump is the highest pressure point in the system.

as far as efficiency for lower temp...You should have checked the efficiency reading on your borrowed combustion analyzer at several return water temps to see what the difference is. haha.

I think it is getting to split hairs, but that is what we have fun doing isn't it ;-)  I would time the dhw cycle the way it is - just to get a feel for runtime - to calculate how much money you would be talking about per year. 

We could calculate the approx. number of btu's for each cycle, estimate times per week and take it times 52 to estimate yearly use.  The first calculation would be for the "approx. 93%" and then...

You have to spend some time to tweak your boiler dhw demand temperature. Ideally you would want the largest boiler delta t (lochinvar recommends) and lowest temp. that will satisfy your demand "quick" enough to meet your dhw demands.  Once you figure that out, I would consider the effic. at that temp.  - note: you won't see anywhere near 98% without it being at least 120 deg. or lower supply temp and minimum 20 deg. delta t.



So it boils down to...what is the cost of your dhw boiler firing for the year at 93% and then just quickly figure what the difference in nat. gas cost between 98-93% to know that would be your maximum benefit to mess with it. Real life will more than likely be somewhere in the middle. Is it worth it?  That is your call.

hope this helps.

BobbyG

hydronic misconceptions

Side Note:  The waters moving too fast - pipe sizing - circulator sizing was all part of my inspiration for my speech:  [url=http://www.youtube.com/watch?v=IYJ03-VOn-0]http://www.youtube.com/watch?v=IYJ03-VOn-0



It is an ongoing issue with people, even in the industry, that think if you slow the water down you will transfer more heat.  Help spread the truth! haha.