Drainback vs. Closed Loop WAS: mixing valves on SHW systems with gas backup

Tom Lane tom at ecs-solar.com
Fri May 16 11:33:23 PDT 2008


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German Resol and Steca DHW controls WILL NOT run if a sensor is either open 
or shorted perfect for drainback . Analog  GOLDLINE WILL RUN 24/7 if a senor 
is shorted on the collector or open on storage  bad news for the customer 
gatortom

----- Original Message ----- 
From: "Karl Schwingel" <karl at northwindrenewable.com>
To: <RE-wrenches at topica.com>
Sent: Sunday, May 11, 2008 11:50 AM
Subject: RE: Drainback vs. Closed Loop WAS: mixing valves on SHW systems 
with gas backup


>
> First, I'd always close that drainback tank, why vent it to the 
> atmosphere?
> Just adding oxygen, and evaporating water, especially at operating temps.
>
>>>>>As for Focus on Energy and bureacracies, dictating design can be
>>>>>problematical, despite the best intentions---------
>
>>>>>Ken Schaal
>
> I agree with almost all of the design criteria for Focus
>
> http://www.focusonenergy.com/files/Document_Management_System/Renewables/win
> d_rewardpreapprovalapplication.pdf  (page 3)
>
> and I am willing to deal with the ones I don't, mostly because it protects
> the industry from what become well publicized disasters.  Unhappy 
> customers
> can have very big mouths.   I've seen the results of what can happen (not 
> my
> work fortunately), and it always seems to become a case of "solar doesn't
> work" or "solar doesn't work up north", and not a case of "the guy that
> designed and installed my system was a hack"
>
> If a boiler doesn't keep the house warm, people don't say "hot water heat
> doesn't work" they blame it on some aspect of the materials or 
> installation,
> because everybody knows that hot water heat can work, because they know
> several people that have it, and they don't freeze.
>
> Every day I discover something new I need to learn.
> Glad to have experienced folks to discuss with.
>
> Karl
>
>
> ----- 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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