Drainback vs. Closed Loop WAS: mixing valves on SHW systems with gas backup
Ken Schaal
ken at commonwealthsolar.com
Sun May 11 05:34:27 PDT 2008
<x-flowed>
Glycol mixtures in the drainback tank seem like a good idea, but they can be
problematical.
First, from my direct observation of a competitors problematic
system ---60-4x8 collectors with a 200 gal drainback that went thru
inadequate HE before going to the collectors. The DB tank is thus the
hottest storage in the system, and when the pump shuts off ,on hi-limit
especially, the fluid returning to that tank can be quite hot, even steamy.
In this case the non-pressurized DB tank was in the basement of a 200 man
prison camp, and the glycol fumes were nauseating. They removed the glycol
and it ran as a straight water DB. Better heat transfer and lower pumping
power also.
Also seems to me there was a discussion on this list a while back about
residual glycols on the interior of absorber tubes at stagnation temps.
Gator Tom had some thoughts on that,I think, or it may be covered in his
book.
Contact off list re. the pumps as we are thinking about rep'ing them to the
solar market, but we're currently helping the manu work out a kink in the
operation of the electronics.
Travis has been Beta testing for us also, and may have some thoughts he'd
like to contribute, if he is OK after the tornadoes that came thru MO
yesterday .
Sure hope so !
Travis-- Are you there?
We started using progessive cavity pumps from Procon many years ago,
mounted to a 1/4 hp motor, when we needed heads higher than 30', the limit
for 009's back then. A few years ago, the head for 009's was ' improved',
now at 35', but that made them more sensitive to cavitation. Since we syphon
the storage water out of our tanks, we usually had about 4' worth of inlet
pressure and when combined with higher temps, cavitation was more likely.
After 20 years of using 009's it was time to look around. Procon was in the
midst of moving to Mexico, and that's when I found the Fluid-O-Tech's. I've
been using them for about 3 years with only a few glitches. A big concern is
the DB bypass, which so far , for smaller systems, is a simple 3/8'' OD tube
on a 1/4 turn valve, mounted in the supply to the collectors pipe , above
the pump. Being positive displacement, there is no DB thru the pump.Being
positive displacement, the pump can draw a suction, although that should be
minimized. But it is real handy when using inground tanks, thus allowing
ground mount arrays.
They're pricy, but just like the solar system, pay for themselves with low
kwh consumption.
As for Focus on Energy and bureacracies, dictating design can be
problematical, despite the best intentions---------
Ken Schaal
Experience certified design/build solar contractor--still learning every day
!
Thank you all
----- Original Message -----
From: "Karl Schwingel" <karl at northwindrenewable.com>
To: <RE-wrenches at topica.com>
Sent: Saturday, May 10, 2008 4:04 PM
Subject: RE: Drainback vs. Closed Loop WAS: mixing valves on SHW systems
with gas backup
>
> A common way to do it up north here is to use Glycol in the drainback
> loop.
> In fact Wisconsin Focus on Energy ( the public/nonprofit that administers
> the state incentive program) reqires that you use glycol to reduce the
> burst
> point of the fluid to -20F,
> (-60F for pressurized systems).
>
> Ken, can you refer me to more info on these sweet pumps you're using? My
> only real beef with drainback systems is the power draw. I'm planning on
> using drainback for most of my systems that are not just small domestic
> hot
> water systems.
>
> On my own system I'd probably do a large water only drainback, pumping
> tank
> water thru the panels. But that's me, and not getting the state rebate
> isn't
> a deal breaker.
>
>
>
> Karl Schwingel
> Nabcep Certified Thermal Installer
>
> NorthWind Renewable Energy
> Karl at northwindrenewable.com
> PO box 723,
> Stevens Point Wi.
> 54481
> cell: 715 209 0446
>
>
>
>
> -----Original Message-----
> From: Ken Schaal [mailto:ken at commonwealthsolar.com]
> Sent: Saturday, May 10, 2008 1:24 PM
> To: RE-wrenches at topica.com
> Subject: Re: Drainback vs. Closed Loop WAS: mixing valves on SHW systems
> with gas backup
>
>
> Hi Bill
>
> Not to worry--' your Dad' is just fine ! Actually, I have an anti-freeze
> system on a rental house next to my office, and for my office radiant
> slab.
> Circumstances dictated.
> ---practically free, used collectors ( Reynolds , all aluminum absorber,
> not compatible with copper HE, and needing anti-freeze for corrosion
> protection)
> ---ground mounted array making drain back impossible at the time.
> note; I now make my own tanks ,which can be in ground if needed, and we
> use a positive displacement pump, with bypass to allow drain back, that
> can
> be mounted at water level, ie. don't need positive inlet pressure.
>
> Of coarse I've had problems, since I've learned from experience over the
> last 30 years. My own experience , plus what I've seen others do, is
> briefly
>
> reviewed below.
> For drainback reliability issues, we should first distinguish as to type
> of
> drainback.
> The typical on the market has a small drainback tank, with integral HE, or
> uses a storage tank with integral HE. The smaller volume of water makes it
> more vulnerable to control or, more likely, sensor wiring failure
> resulting
>
> in continuous pump operation, which in freezing weather may eventually
> result in a frozen absorber. If this type of system is used, a freeze
> sensor
>
> to prevent operation with collector temp below 40 + would be best, and
> sensor wiring should have particular attention paid to critter damage like
> squirrels, vultures, or ice, hanging or sliding. Piping is also vulnerable
> to the ice issue as well. The tank sensor needs to be cared for well also,
> since a break in that wire will cause the control to keep the pump on.
>
> One important consideration for piping, including horizontally mounted
> collectors, is the relationship between slope and pipe diameter. The
> smaller
>
> the pipe the greater the slope needed to overcome the surface tension of
> the water within the pipe. At 1" dia. the pipe can be minimally
> sloped--1/16 to 1/8"/ ft of run, even dead level if you are very trusting
> of
>
> your level and the run is only one or two internal header collectors.Even
> if
>
> 1" pipe is 1/2 full of water, the freezing water will not expand enough to
> split the pipe. Too much slope on the collector keeps the upper capped off
> header full of water, which, if the solder has not flowed well around the
> cap, can eventually lead to failure of the solder bond, from freeze/thaw
> cycles, with consequent complete failure of the bond, and the cap popping
> off, usually when the collector fills at stagnation temps after a sunny
> day
> power outage. Some of the German controls are nice as they have a
> collector
> hi limit in addition to the storage hi limit. Goldline, since Hayward
> bought
>
> them, doesn't seem very interested in advanced features, last we checked.
> But they are quite reliable and have more robust relays.
>
> The other drainback type uses a large volume tank-- our are 2gals/sq ft of
> collector, usually-- with the HE submerged in the storage water, either
> copper coils or SS tanks ( my preference) for better performance.If the
> pump
>
> runs continuously, it is much less likely to freeze since there is enough
> heat in storage to go thru the night and then be reheated the next day.
>
> Generally this type of drainback is used for larger commercial systems,
> where Btu's/ $ are looked at closer, and multiple 80 or 120 gal tanks get
> expensive, take up too much space, and are a pain in the ass. Since we
> make
> our own tanks, we use them for residential as well. They can also easily
> be
> made from poly tanks. We used to get our from Chem-Tainer. There is still
> a
> picture on my old website. www.commonwealthsolar.com
>
> Gravity has been pretty reliable, but air venting to allow the collector
> to
> drain needs to be virtually foolproof.!
>
> Others can probably add to this list of caveats.
>
> As for why the European imports are all anti-freeze, maybe it's because
> their primary market is newcomers who don't have experience , and so long
> as
>
> the connections are tight, the temp gauge will get hot, and most
> homeowners
> think hot is good, not understanding that energy saved is more than
> temperature ??
> If I was exporting I wouldn't want installer problems either, and how many
> residential systems are performance tested ?
> A typical large tank drainback in Virginia, with typical residential load
> patterns, gets 650-750 Btu's/ sq ft/ d annual average.
>
> What do others think of the imports ??
> They do look slick though !
>
> And there's room for all !
>
> Typical for us, we had a call for service last week, from a customer that
> got a large tank drainback in '84. Control got zapped by lightning. Also
> switched out the 009 pump (160W) for our new progressive rotor w/ inverter
> based electronics that uses about 30 watts for 30 ft head applications.
> Good for another 20 years?
>
>
> Take Care
> Ken
>
>
> In
> ----- Original Message -----
> From: "Bill Loesch" <solar1online at charter.net>
> To: <RE-wrenches at topica.com>
> Sent: Saturday, May 10, 2008 8:34 AM
> Subject: Drainback vs. Closed Loop WAS: mixing valves on SHW systems with
> gas backup [RE-
>
>
>>
>> Hi Ken,
>>
>> I'm changing the subject as this has almost nothing to do with the
>> initial
>> subject and the potential to deteriorate into a "my Dad can whip your Dad
>> scenario".
>>
>> I am very pleased that you have had no(?) problems with drainback systems
>> or
>> electronics or plumbing as well as gravity.
>> I wish you continued success.
>>
>> There have been a plethora of SDHW system manufacturers entering the
>> North
>> American market, primarily European, and I have not seen one of their
>> systems utilize anything but closed loop principles. Food for thought?
>>
>> Bill Loesch
>> Solar 1 - Saint Louis Solar
>>
>>
>> ----- Original Message -----
>> From: "Ken Schaal" <ken at commonwealthsolar.com>
>> To: <RE-wrenches at topica.com>
>> Sent: Saturday, May 10, 2008 5:35 AM
>> Subject: Re: mixing valves on SHW systems with gas backup [RE-wrenches]
>>
>>
>>>
>>> As we approach the summer season, and overheating of anti-freeze
>>> systems,
>>> it's a good time to remember that drainback designs require nothing but
>>> gravity to prevent dangerous temperatures that lead to increased
>>> callbacks
>>> and maintenance problems. Not to mention the liability issues of
>>> scalding
>>> water, and the increased corrosion activity in the tank.
>>>
>>> Ken Schaal
>>> CommonWealth Solar
>>>
>>>
>>> ----- Original Message -----
>>> From: "Travis Creswell" <tcreswell at ozarkenergyservices.com>
>>> To: <RE-wrenches at topica.com>
>>> Sent: Saturday, May 10, 2008 6:09 AM
>>> Subject: RE: mixing valves on SHW systems with gas backup [RE-wrenches]
>>>
>>>
>>> >
>>> > The same thing can happen on electric water heaters with "Energy
>>> > Smart"
>>> > controls.
>>> >
>>> > Yes, thermal questions are allowed and I would like to see more.
>>> >
>>> > Travis Creswell
>>> > Ozark Energy Services
>>> >
>>> >
>>> > -----Original Message-----
>>> > From: Karl Schwingel [mailto:karl at northwindrenewable.com]
>>> > Sent: Friday, May 09, 2008 10:00 PM
>>> > To: RE-wrenches at topica.com
>>> > Subject: RE: mixing valves on SHW systems with gas backup
>>> > [RE-wrenches]
>>> >
>>> >
>>> > Davis,
>>> >
>>> > What I've heard is that you run the risk of tripping the overthermal
>>> > protection in the gas water heater if you should on a hot summer day
>>> > run
>>> > 190
>>> > deg water into the bottom of the tank. Of course you don't realize it
>>> > till
>>> > months or weeks later when there's no solar preheated water and you
>>> > get
>>> > the
>>> > call that "my water heater doesn't work"
>>> >
>>> > I've never put a mixing valve on the preheat tank, and have only seen
>>> > it
>>> > done when you want to keep the tank at a high temp (such as when
>>> > you're
>>> > pulling water off for a space heat loop. However, I'm working mostly
>>> > around
>>> > electric water heaters.
>>> >
>>> > Is this forum open to thermal questions too? All I've seen so far has
>> been
>>> > PV related.
>>> >
>>> > Karl Schwingel
>>> > Nabcep Certified Thermal Installer
>>> >
>>> > NorthWind Renewable Energy
>>> > Karl at northwindrenewable.com
>>> > PO box 723,
>>> > Stevens Point Wi.
>>> > 54481
>>> > cell: 715 209 0446
>>> >
>>> >
>>> >
>>> >
>>> >
>>> > -----Original Message-----
>>> > From: Davis Terrell [mailto:davis at brightearthsolar.com]
>>> > Sent: Saturday, May 10, 2008 12:28 AM
>>> > To: RE-wrenches
>>> > Subject: mixing valves on SHW systems with gas backup [RE-wrenches]
>>> >
>>> >
>>> > Wrenches,
>>> >
>>> > I have seen some literature call for a mixing valve in between the
>>> > solar
>>> > storage tank and the gas hot water tank. Can anyone give some ideas
>>> > as
>>> > to why this second mixing valve may be necessary? Does anyone else
>>> > use
>>> > one? Thanks.
>>> >
>>> > --
>>> > Davis Terrell
>>> > Bright Earth Solar
>>> > (802) 492-2273 / brightearthsolar.com
>>> >
>>
>>
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