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tie in SHW to commercial boiler room (23 Posts)
tie in SHW to commercial boiler roomI am installing a SHW system on a 9 story building. I having troubles of where to connect in the solar hot water line for the storage tanks.
The mechanical room set up is a little tricky. I am not sure where to connect the SHW hot out ofthe storage tanks . Usually I would connect to the auxiliary tanks coldinlet, but the way it is plumbed it may not be possible (see attached
drawings and pictures).
The cold inlet to the Aux. Tank also has the hot out from the boilers
connected at the same point for tempering purposes. There is no mixing
My option number #1 is to tie-in to the boiler.
Option #2 tie-in to the existing setup at the cold water inlet and downsize
the pipe to keep the the water tempered. Option 2A, an injection pump at
the cold inlet (not on drawing).
Option #3, Re-route the hot water recirc
line hot out line from the boiler. Eliminate the CWS to the auxiliary tank
(including the hot line from boiler) and replace the CWS as usual with the
solar hot water line.
Would you guys think?
MichaelThis post was edited by an admin on June 6, 2012 2:16 PM.
#2Doing #2 would work, but solar energy wouldn't get used in the recirculation loop.
Relocating the recirc. return to the cold side of the solar tanks would solve that.
I don't quite understand what #3 is trying to accomplish.Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
what aboutfeeding the hot (red line) from the solar to the cold supply? no need to pump, the cold just flows thru the solar for pre-heat.
Don't really want to mix the solar tank with a pump or recirc, you want that tank to stratify.
Is there a thermostatic valve on the output? fairly common on large systems and for liability issues. If so the recirc needs to be piped correctly to prevent temperature creep.
Number 2 ...# 2 Is always my standard option. But the buildings engineer came up with Number 3. Number 1 was the facilities MGR idea.
On #2, The Engineer is worried about the solar mixing with the hot from the boiler since they tie in together (see photos). Valid point, but there is not many options. The Aux. Tank is a 500 gallon tank. Once the Solar Pre heated water hits it, the boiler will not fire. He still does not like it!
I'll attach an updated drawing.
Thanks for the input
Boilers will fire all night without water drawIn a system like this, the recirculation loop, if it's not insulated, accounts for over 30% of the heat used by the water heaters.
Without usage by tenants, there is no way to get solar heat from the solar tanks to the auxiliary tank. So the boilers will fire all night even in the summer when you could be on 100% solar.Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
KevinI am aware that the tanks may sit hot all night without draw. Do you have an idea to get around that?
Using Solar for standby losses"You can install a 3/4" line from the aux tank to the cold line going to the solar tanks. In that line is a check valve and pump connected to a differential control. The pump kicks on when aux. tank temp drops below solar tank temp. (say delta T=5F ON, 3F OFF)"
It's like you are pretending that the solar tanks are solar collectors, and the aux tank is solar storage.Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
an extra pumpKevin,
I like your idea, but I don't want to add another pump for one simple reason; I would have to add a separate controller.
I am using an EnerWorks System (not by my choice) and they have a pump station that has a controller designed into it (they call it CSET). Looking at their spec sheet there is not a relay to add a pump. What I COULD do is add a small plugin recirc with a timer. This would at least circulate the heat from the solar tanks into the aux tank.
I am attaching a updated drawing with your suggestion on it.
Thanks for your helpThis post was edited by an admin on June 13, 2012 10:02 AM.
Enerworks engineer wants me to do it this way:The Enginner at EnerWorks solar want it plumbed the way in the attached drawing. Which I do agree with to a point.
Is has been impossible sourcing a mixing valve for three inch. And if I do find
one, the cost is going to be indecent. I would like to re-figure this so the
piping for the tanks and through the mixing valve are 2". What will this do to
the flow rates and pressure drops?
If I have to go 3" for piping that is fine, but the cost are going to be
astronomical and blow the payback out of the water. BUT most importantly I
want this system to function properly.
Thanks for all your help on this.
RecircHR is right, leave the solar out of the recirc. loop.
But how do you get solar to make up the heat lost by the recirc loop?
You can install a 3/4" line from the aux tank to the cold line going to the solar tanks. In that line is a check valve and pump connected to a differential control. The pump kicks on when aux. tank temp drops below solar tank temp. (say delta T=5F ON, 3F OFF)
recirc integration with solar preheatAs Kevin pointed out above, in a lot of buildings the recirc load can make up a large fraction of the total apparent DHW load. (I recently looked at a handful of high schools that are closed all summer with zero HW load but the boiler still runs pretty much non stop because nobody turns off the recirc). This load is often totally ignored when building solar systems and I think it is a real weakness of a lot of commercial solar system designs I've reviewed.
What we do when we build solar preheat systems for buildings with 24/7 recirc lines is to plumb the recirc return to a 3 way valve. We then control that three way valve with a second dT controller (we use a Tekmar 156 so it isn't confused for the solar controller): Whenever the solar tank is 20 degrees hotter than the recirc return, the valve opens and the recirc return runs to the solar tank inlet (or the mid height recirc port if it exists). If the solar tank temp falls to within 10 degrees of the recirc return the valve closes and the recirc return water again flows to the cold inlet of the backup tank (the line connecting solar preheat tank to backup water heater).
This simple upgrade allows the solar to help offset the recirc load when available, and yet keeps the recirc line from ever inadvertently heating the solar tank. It also ensures that the coolest available water is always in the solar tank (and thus increases solar collector efficiency).
There's NEVER a Reason for 24/7 Recirc"What we do when we build solar preheat systems for buildings with 24/7 recirc lines is to plumb the recirc return to a 3 way valve. We then control that three way valve with a second dT controller "
The other thing you should do is prevent the recirc pump from running 24/7. Timers and aquastats are a traditional way, but not the best way. Demand control is the best way:
At least make sure the recirculation pump isn't oversized. Erosion corrosion is a common problem in 24/7 recirculation loops: http://www.croberts.com/erosion-corrosion.htmThis post was edited by an admin on June 14, 2012 1:38 AM.
The 24/7 recirc is there to stay. I had a meeting with the mech. engineer of the bldg today. He is adamant that i do nothing to interfere with it.
I like what Fortunat proposed above in his reply. I would not rather use a three way though. I will if that is the best approach. I like having the pump on a differential tied in to the DHW out the Aux. tank, back into the cold supply to the solar tanks. I have not ruled out a three way valve.
I really appreciate everyone's opinion's on this and I am open to further discussion. Thanks again dan for this great forum!
MichaelThis post was edited by an admin on June 14, 2012 5:54 PM.
I agree with you that the out of control recirc is the problem, we don't always have the ability to affect that. When we do the whole mechanical system (as we often do in residential projects, we insist on a smarter recirc (or the smartest of all...no recirc).
In other projects we try (where possible) to convince building owners and mechanical contractors to get the recirc under control (timer, aquastat, occupancy sensors), but in cases where we are just the 'solar guy' we don't always succeed. In those cases the best we can do is size the solar to include that recirc load and design it intelligently enough so that it can.
oversized recirc pumpsEvery existing commercial system I've seen, and every residential system I'd seen until the past couple of years has had an oversized pump. Most are MASSIVELY oversized. Chalk it up to typical old-school pump sizing "rules of thumb" and lack of post-install field measurements.
I just did a midsize hotel remodel (77 rooms, 5 stories, 2 kitchens, 7 public RRs) using two Laing ecocirc E3's (about the size of your fist and draw ~15W apiece.) I haven't had a chance to measure actual flow yet, and the piping was far too complex to estimate friction head, but I ordered one on a hunch just to see if it would work, despite the project engineer's suggestion of pumps roughly 3x the size (and 5x the power consumption.) The E3 worked perfectly for one tower (about half the building) but wasn't quite enough for the whole place. So we bought another and zoned the recircs. Controls come next, but even now it's working like a charm. Piping is a combination of Aquatherm and PEX, not even fully insulated yet, though carefully routed in a multiple-reverse-return configuration, I haven't even started to tune the recirc, but we're going to do that this winter (by adding Uponor EP inline valves wherever the return temps are high.) The ecocirc has a variable speed control onboard - we're running them at about 60% of the knob setting right now. Once winter sets in and the rest of the insulation is on, we'll go back with thermometers and dial it in.
and what is that 3-way valveFortunate,
About your comment:
" for buildings with 24/7 recirc lines is to plumb the recirc return to a 3 way valve. We then control that three way valve with a second dT controller "
I also have this in mind as a great way to mix in solar to recirc, but I have not been able to find a controllable 3-way valve that is rated for potable water (for less than $500). What is the valve you use?
By the way, you can cut the runtime of the recirc pump down a lot with an aquastat. Let the line cool off 20 degrees or so. The strap-on Honeywell with adjustable differential is an inexpensive upgrade
And I strongly recommend looking at the typical details that Powers, Leonard, and other tempering valve companies publish for recirculation with building mixing valves because you really do need to split the recirc return into both sides of the building tempering valve to make sure the recirc pump lets the valve deliver tempered water and NOT hot straight out of the tanks.
3 way valveJamie,
We generally use a Caleffi three way valve:
I couldn't tell you what it costs, but it isn't 500 bucks. It is Brass, Stainless and EPDM and is high temp capable so I don't know why it wouldn't be good for DHW applications.
I totally agree with you about recirc line controls including aquastat, timers, occupancy sensors etc. Though it isn't often done, I tend to argue to put the aquastat out at the far end of the recirc line (might as well turn off the pump as soon as hot water reaches the farthest fixture rather than wait for it to come all the way back to the boiler room).
On a similar noteHi All,
Glad to see so many solar thermal people here. I have a similar issue. One of our clients has no room for a dedicated solar storage tank on the roof or in the mechanical room.
The existing oil boiler feeds five 12000 L storage tanks through heat exchangers for DHW use. There are also 5 recirc lines (zones)
Its a commercial system for a hotel with 50 ET collectors. We are investigating tie in strategies and the two that make most sense to me are
- Tie in to the boiler return line.
- Tie in to the recalculation lines.
Any thoughts are appreciated.
www.mustakbalct.comThis post was edited by an admin on June 28, 2012 5:26 AM.
I wouldn't do either of those two things as I think the solar performance will be unsatisfactory in either case.
When you tie into the recirc line or the boiler return line you don't give the solar system the opportunity to work on cold water (where it is most efficient). I'm not sure where this project is located, but there is a pretty significant efficiency penalty associated with the required higher collector temperature (as much as 50% or better) when the collectors need to run at 140 deg F vs 80 or 90 degrees when preheating cold water.
I'd look again for tank space, or consider replumbing and repuposing one of the 12,000 l water heaters as a solar storage tank. Though it adds to the complexity, you'll end up with a much better system than trying to have the solar heat the water which has already been heated by the oil boiler.
Our hands are tiedFortunat,
I agree with you that it would be ideal not to do either. We have tried to demonstrate that to the client and the A&E firm using polysun simulations (with/without) storage. To cut a long story short the client and his A&E firm are insisting on no dedicated solar storage and to secure the project we had to offer the no dedicated solar storage solutions.
The project is located in the Dead Sea in Jordan, DNI is almost 2600 kWh/m2/year. So during the summer months the solar will be able to contribute and heat the tanks and leave the boiler off. However as you mentioned its during winter that when the boiler fires (heating already hot water is not efficient). I have attached a file that demonstrates the technique of recirc reheating.
If we have no choice, shall we go for recirc heating or boiler return heating ?
lesser of two evilsAla,
At the risk of sounding self righteous, I think that sometimes it is worth walking away from a job when a client is stubborn or demands a system design which doesn't make sense. At the end of the day, though they insist on something, your professional reputation is still at stake when the system dissapoints. Having said that, we all have to feed our families so obviously sometimes we do a project with a design we don't love. In that case, we just hold our nose (and put very explicitly in writing to the client and anyone who will listen that we think there is a better way). But I tend to draw the line that if I am embarrassed to put my name and logo on the sticker in the basement, then I suggest the client find someone else to put the system in.
This case may not be that bad. As you note, you are in a fairly mild climate with excellent insolation and it sounds like you are using Evacuated tubes which should help minimize the performance penalty of higher operating temperatures somewhat.
If choosing between heating the boiler loop return or the recirc return, I think I'd choose the latter (assuming the flow rate is sufficient to move the heat). If you heat the boiler loop, then you not only increase the required temperature even further, but you also add the boiler heat loss to your total load and for a big oil boiler (1 MMBTU/hr) with a natural draft flue that can be several hundred thousand BTU's lost up the chimney and through the boiler jacket each day. Those are BTU's that you'd rather have in the tank is possible.
As Dr Mahjouri's paper points out, this has been done before (and we've
actually done a system like this too). Though one difference is that I think both the thermomax
system and thh system we did like this was in a building with minimal actual DHW demand (where the recirc was the dominant load). I don't think that will be the case in your hotel.
That is my 2 cents. Good luck with it.
CheersIts a good thing I dont have kids yet, so we can actually walk away from this one. Will share the results in the future. Thanks for your help.
AlaThis post was edited by an admin on June 28, 2012 10:13 AM.
appologiesfive 2500 L tanks totalling 12500.