Drainback vs. Closed Loop Circulators [RE-wrenches]

Wed Jun 7 11:19:16 PDT 2006

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Hi Ken,
No confusion between Draindown and Drainback here.
And I don't mean to imply that our experience with drainbacks is universal.
Just reporting in from the feild without a lot of detail.
My opinion on the issue is that you go to a drainback for a space heating 
system but stick to a closed loop for SDHW.
your glycolhead,
Conrad Geyser
Cotuit Solar

----- Original Message ----- 
From: "Ken Schaal" <ken at commonwealthsolar.com>
To: <RE-wrenches at topica.com>
Sent: Wednesday, June 07, 2006 8:57 AM
Subject: Re: Drainback vs. Closed Loop Circulators [RE-wrenches]

>
> Let's be sure we are not confusing DRAIN DOWN -- using a motorized valve 
> to
> shut off pressurized water going to the collectors-- with DRAIN BACK , 
> which
> uses a pump to lift unpressurized water to the collector, and drains back
> into the reservoir/tank by gravity when the pump shuts off. The collector
> and piping must be sloped to drain [ even plumbers can understand that 
> part
> ! ] and there must be a way for air from the tank or reservoir to get into
> the return line, thus allowing the collector and piping to drain.
>
> Travis comments are right on target !
>
> The only time I have used glycol for a new system is when the bottom of 
> the
> collector cannot be above the top of the water level in the tank .
> Incidentally, the first systems I installed in 1977-78 were draindown and
> then we started using various versions of drain back. A typical tank is
> shown on my website www.commonwealthsolar.com/cwhot.htm
>
> As for pumps and high power requirements that was /is a concern, although 
> as
> Travis has shown the reliability and efficiency gains more than 
> compensate.
> For years I used Taco 009B pumps, syphoning water from the bottom of the
> tank. Recently Taco has 'improved' the performance of these pumps head
> capacity, which made them more sensitive to cavitation. This got expensive
> and frustrating ! For 6 mos I have used Fluid-o-tech TMFR pumps which use 
> a
> converter to provide 3 phase to the pump. Total watts on a Brand meter of
> 20-30 at 30' head and 1-2 gpm. A bypass line is required to allow 
> drainback
> .
>
> Please contact off-list for more info.
>
> Thanks to all for the chance for an old SHW guy to learn PV !
>
> Ken Schaal
> CommonWealth Solar,LLC
> 804-798-5371
>
>
> ----- Original Message -----
> From: "Travis Creswell, Ozark Solar" <ozsolar at ipa.net>
> To: <RE-wrenches at topica.com>
> Sent: Wednesday, June 07, 2006 1:04 AM
> Subject: RE: Drainback vs. Closed Loop Circulators [RE-wrenches]
>
>
>>
>> Hey Jeff and Conrad,
>>
>> How neat is this?  We're actually talking about SWH on the wrenches list.
>>
>> Sounds to me like the drain back systems Conrad is talking about weren't
>> installed properly.  The type of drain back I'm talking about does not
>> require a motorized spool valve or a vacuum breaker.  I think there were
>> several other variations on that same bad theme as well.
>>
>> I can't imagine any potable water being so corrosive that it would ruin a
>> non-ferrous pump and copper collectors.  If that was the case wouldn't 
>> the
>> water be damaging the houses potable plumbing and appliances as well?
>>
>> Something tells me they used cast iron pumps and didn't install the
>> collectors and plumbing properly (positive drain).
>>
>> I thought about the two pump set up before but to me it adds unnecessary
>> complexity to the system.  Personally, I'll stick with the one pump set 
>> up
>> and use a line voltage controller.  I've used Tekmar controllers for
> radiant
>> heating and they are the cat's meow but I'd rather not use an expensive
> (2x)
>> controller that requires a power supply which plus a junction box for the
>> extra stuff.  I'm just a KISS guy.  Several hundred dollars of extra
>> equipment and labor plus a few more things to break add up to higher life
>> cycle cost.
>>
>> The key benefits to a drain back system as I see them
>>
>> -Fewest parts = All it needs is a pump, differential controller, and few
>> isolation and drain/fill valves. So that means the easiest install and 
>> the
>> fewest parts to break and require service.
>> A glycol closed loop requires and air bleeder, expansion tank, pressure
>> relief valve and check valve.
>>
>> -No glycol to service.  Water never turns acidic, glycol does. I've heard
>> stories (fairy tales?) about glycol lasting 20 years but it's definitely
> not
>> the norm in my personal experience with the 100's of closed loop glycol
>> systems that I've laid my hands on over that last 15 years.  Even if it
> does
>> last 20 years you still need to be checking the PH regularly.  You can't
>> trust the home owner to do that so that means an extra expense for the
>> glycol system owner.  But then again service contracts are good for us
> poor
>> wrenches.
>>
>> -Higher efficiency.  Water will collect and transfer more energy then
>> glycol.
>>
>> -Power failures don't lead to problems with the type of drain back I'm
>> talking about.  A power failure in a closed loop glycol system can easily
>> stagnate the system.  If the pressure relief goes off a few times the
>> pressure often drop below the minimum head required to pump.  This is 
>> main
>> service call I've gotten for closed loop glycol system over the years.
>>
>> -Lowest Life Cycle Cost.  Fewest parts initially and no need to ever
> change
>> the glycol out.   After a few stagnation events the closed loop glycol
>> system will need recharged which is service call you'll never have with a
>> drainback.  No chance of damaging the collectors assuming they are
> installed
>> correctly which is really easy to do.  If the pump fails or electricity
> goes
>> out the system drains out.
>>
>> That's just my .02 and I'm very open to other ideas.
>>
>> Best,
>> Travis Creswell
>> Ozark Energy Services
>>
>>
>>
>> -----Original Message-----
>> From: Jeff Clearwater [mailto:clrwater at earthlink.net]
>> Sent: Tuesday, June 06, 2006 12:55 AM
>> To: RE-wrenches at topica.com
>> Subject: Re: Drainback vs. Closed Loop Circulators [RE-wrenches]
>>
>>
>> Hey Conrad,
>>
>> Is the drainback of the '80s a fair comparison to the drainback of today?
>>
>> It's the failures of '80s glycol that pushes us to drainback.  But
>> then again is the glycol of the '80s a fair comparison to the glycol
>> of today?
>>
>> The debate goes on.
>>
>> Travis, you said "all the benefits of drainback" - Want to spell that
>> out for us?
>>
>> Conrad, game to do the same for glycol?
>>
>> Still Learning,
>>
>> Jeff C.
>>
>>
>>
>> >Jeff, Travis and other Drainheads,
>> >
>> >If you want to cut the power use more you can use two smaller
>> >circulators, cutting the second one out after 5 minutes (once you
>> >know you've filled the collector).
>> >Tek-Mar controller provides for this through a programmable second
>> output....
>> >.
>> >BTW, out of the several hundred 80's systems that we've serviced
>> >here in the northeast, there is yet to be one surviving drainback.
>> >Some day I'll try to catalog this in the hopes of solutions.
>> >for starters:
>> >-corrosive drainback water?-circulators failing quickly and
>> >collectors corroding
>> >-freeze ups
>> >
>> >Those glycol loops sure hold up....
>> >
>> >Conrad Geyser
>> >Cotuit Solar
>> >
>> >----- Original Message ----- From: "Travis Creswell, Ozark Solar"
>> ><ozsolar at ipa.net>
>> >To: <RE-wrenches at topica.com>
>> >Sent: Monday, June 05, 2006 3:52 PM
>> >Subject: RE: Drainback vs. Closed Loop Circulators [RE-wrenches]
>> >
>> >>
>> >>Hello Jeff,
>> >>
>> >>We just did a drain back system with six 4x10 flat plates. 
>> >>Calculations
>> >>showed that we had to use Grundfos 26-96 to overcome the head and total
>> >>pressure drop.  I carefully added up every foot of pipe, valve, elbow
> etc
>> to
>> >>make sure I didn't oversize it.
>> >>
>> >>It's rated at 215 watts but we choked the flow down to ~9 gpm (1.5 per
>> >>panel) and dropped the wattage to 135 as measured with a Brand power
>> meter.
>> >>
>> >>The pump would do almost 20 gpm with out reducing flow which was higher
>> then
>> >>the charts said it would do so I assume there was a siphon effect 
>> >>adding
>> to
>> >>the flow.  But you can't factor that into the pump sizing as you have 
>> >>to
>> >>overcome the head initially.  And the next smaller pump left no room to
>> >>safely overcome the head plus it didn't use much less wattage.
>> >>
>> >>I'll gladly use the extra energy to get all the benefits of drain back.
> In
>> >>the morning I saw a 20f delta t at 9 gpm.  Of course the Delta T drops
> as
>> >>the days goes on but stays above 10.  That's 90,000 BTU's of heat for
> 460
>> >>BTU's worth of electricity.  So the average of the day that's 1% of the
>> >>energy collected is used to pump.  Share that with the "thermal
> engineer"
>> >>and see what he says.
>> >>
>> >>The common circulation pump is centrifugal which is not a positive
>> >>displacement type.  Very low wattage positive displacement pumps are
>> >>available that can handle the temp but their flow rate limits them to a
>> max
>> >>of several panels.  Ken Schaal of Commonwealth Solar can speak with
> direct
>> >>knowledge of them.
>> >>
>> >>Best,
>> >>
>> >>Travis Creswell
>> >>Ozark Energy Services
>> >>
>> >>
>> >>-----Original Message-----
>> >>From: Jeff Clearwater [mailto:clrwater at earthlink.net]
>> >>Sent: Friday, May 19, 2006 7:56 AM
>> >>To: RE-wrenches at topica.com
>> >>Subject: Drainback vs. Closed Loop Circulators [RE-wrenches]
>> >>
>> >>
>> >>Hi All,
>> >>
>> >>We have been getting back into offering Solar DHW - mostly due to two
>> >>factors that make it a doable business model in terms of
>> >>installation, service and liability.
>> >>
>> >>The first is switching to evacuated tube collectors.  They are light,
>> >>easy to ship and handle and easy to install - I don't have to worry
>> >>about cranes or major racking weight and it eases safety factors with
>> >>my installers.
>> >>
>> >>Second is going with drainback instead of closed loop glycol.   This
>> >>eliminates having to service the glycol every 2-3 years and actually
>> >>gives a chance that the system might live on when the folks sell the
>> >>house etc.
>> >>
>> >>However, I recently suggested drainback, closed loop to a low income
>> >>zero energy home development we are working with and the thermal
>> >>engineer came back with data saying that the drainback circulators
>> >>used up to 1/3 of the energy harvested by the system in terms of
>> >>electrical cost vs. gas saved!  I find that hard to believe. He
>> >>claimed the closed loop circulators use less but still was showing a
>> >>significant percentage.  I'm not sure whether he's just finding an
>> >>excuse to go with what he is used to or whether there is a
>> >>significant difference here.
>> >>
>> >>So the questions for my esteemed wrenches are:
>> >>
>> >>1)  Does anyone have KWH use figures for solar DHW circulators?
>> >>2)  Does anyone know of the most efficient circulators?  (are
>> >>circulators positive displacement pumps?) - any models to suggest for
>> >>drainback?
>> >>3)  Do folks recommend using PV direct pumping for drainback?  What
>> >>controller would one use then?
>> >>
>> >>Thanks!
>> >>
>> >>Jeff C.
>> >>
>> >>--
>>
>>
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