Solar Pumping Station & Controller

Andrew Hagen_2

I tend to agree. Drainback does not have to add much cost to the project either. You have to buy the drainback tank, but you also save the cost of the heat dump and glycol.

Dobber

Solar Pumping station & controller

Looking at my first solar job. Will be used mostly for mid-temp space heating (panel rads & clip-up)with domestic being pre-heat through 2nd coil on storage tank to oil water heater. So I am looking for something that will look after panels and space heating when temp allows and solar dump when necessary.I think I would prefer a packaged system.

Thanks
Dobber

Andrew Hagen_2

Solar Package

Caleffi has some nice package kits.

Heliodyne also has excellent kits.

hot_rod

A dual coil solar tank

80 gallon kit, with the Caleffi Plus controller option NAS30040plus, and the optional NA26710 3 way zone valve would do this.

The 3 way 120V zone valve connects right onto the solar pump station. The control runs the solar and dump zone. The boiler DHW priority, or any aquastat, could fire the upper coil for back up. The tank does have an upper thermostat well that the boiler DHW sensor fits into.

hr

Wayco Wayne_2

I have the

Calefi isolar plus. I like it's variable speed output. I havent figured out how to set it up for heat dump yet but will figure that out as soon as I get the heat dump piped. With the days getting longer and my tank temperatures climbing I better getr dun. WW

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Paul MacDougall

Is a heat dump absolutley necessary. I have never installed a solar system, but I have talked with installers that say it isnt. They use a function on the control.

hot_rod

dump requirements

depends on how much collector to storage ratio you have. How consistent of a summertime load? And which type of collector. Both flat panels and evac tubes do crank out some serious temperatures in the summer month, if you don't have a place to use the energy, a dump may be needed.

There are a few ways to handle this if in fact you generate more than you use.

Many of the new solar controls have overheat protection, which allows the tank to overcharge above setpoint.

Some have a re-cooling function which allows the solar pump to run at night and rid some heat.

Some suggest running the pump in hand mode, 24/7 if you leave town in the summer months.

An evac tube function on the control is also inportant if you use an evac tube collector.

If all the above doesn't handle overheating and your tank trips the T&P, or you start breaking down the glycol due to excessive stagnation, then you might consider a dump zone.

Caleffi, for one makes this simple with a 3 way ZV kit that connects to the Solar Pump Station to feed that dump. The I-solar control is pre-programed to handle this function.

Some of the evac tube manufacturers sell dump "radiators" for outside.

Cedar Mountain Solar uses a radiant zone, garages for example as a dump zone on large array systems. Follow their articles in PHC News for examples.

Generally a 1.5 - 2 gallon of storage to square foot of panel will work with the overheat and maybe re-cooling feature. large arrays designed for heating loads with small summer dhw loads and tight storage will be prone to OH problems. Use it or lose it, is the old saying.

Or if you know that you will have overheating issues due to low summer use, a drainback system may be better choice.

hr

rt_2

Last August, was when I lit off my evac tube closed loop system for the first time. I experienced a problem with loosing alot of heat in my storage tank at night. I had a check valve in the loop but I was still loosing heat. 30 to 40 degrees F. What I found was that Thermal Syphoning or Gravity Circulation was happening. The check valve was only a swing check and it was allowing the fluid to flow through it. Thanks to some advice from people on this forum, they recommended I install a flow Control valve made by B & G (Bell & Gosset). I did and this solved all my problems. It's a spring loaded check valve which uses a ball. It also has a knob which I can put the valve in Bypass mode there by it will be open all the time. My controller is set for 180 degree max temperature. I'm going to try to use this bypass feature during the summer months which will allow the fluid to circulate at night after the circulator stops thereby saving energy from not using the circulator and saving wear and tear on the circulator. We'll see.

Rene

hot_rod

Check the temperature ratings

on any component you put in the solar piping. Sometimes typical hydronic temperatures are a bit low. The checks, on both supply and return to the panel are a must.

Look for a solar rated check with a 1/2psi pop. This is what is inside the solar pump stations you see. A stainless steel disc, that seats to a brass seat. No rubber or teflon to allow 350F operating temperatures.

Now you see how thermosiphon could be used to cool down a tank if you lock open those "gravity gates" checks for summertime "out of town" overheat protection.

The checks in the pump stations have a 45 degree position to lock them open for draining the panels or overheat, via thermosiphon, protection.

hr

hr

rene_4

Hot Rod,
Who manufactures those check valves and can they be purchased from a plumbing supply house? Any idea what the pipe size is?

Rene

Stephanie Custis (yes, Mark's wife)

You might get better answers

if you typed without the typical BB (Bulletin Board) abbreviations.

Metro Man

Back on my soap box.

I am personally totally against any kind of heat dump for a solar system. It makes no sense to me to design a system to be as efficient as it possibly be then add more power consuming mechanism(s) to it to protect it from itself. Drain back water systems are by far the simplest and efficient systems out there and is all we have installed for 26 + years. . Client goes away to visit Dan in Hawaii for a month..... just shut it off. No stagnation, no expansion, no problems.

This trend in new solar control design w/built in functions to auto switch to your dump zone further perpetuates this flawed design thinking.

If going with glycol, use good quality glycol and size your expansion tanks for worse case and make sure you have somewhere to catch the glycol when it blows. If the power goes out in the middle of the summer and your relying on a dump zone.... boom!

my 2c
Metro Man

hot_rod

I've never

designed or used a dump zone on any of the closed loop glycol systems I have installed for 30 years now

I think the overheat protection methods were designed for mainly for evac tube collectors, or large arrays and undersized storage. I've yet to see a drainback evac tube system, with any track record. So the overheat protection and dump radiators were designed knowing that evac tube collectors will far exceed what any glycol can handle.

If the collector to storage ratio is right for your climate, really flat panel collectors behave pretty well.

Instalations that see frequent power outages would probably be better off with a PV powered pump, same for off griders

Drainbacks are all but unheard of in Europe.

That being said I see a number of solar manufacturers with drainback modules at the European shows. They are starting to see the drainback advantage with large array, typical on heating systems.

hr

Metro Man

high temps...

So why do you need storage temps over 180*F anyway? Pressurized storage tanks can't take it, way over domestic hot water needs, radiant heat... etc.. Would rather have a higher volume at usable temps anyway. The evac tube systems I have seen get the element or tube exchanger dill-e-bober go to high temp but then it has to exchange to the glycol solution. The glycol then has to exchange to potable water or storage so you have 2 exchanges in some cases going on. It's at the "element" that is the problem. Kind of like sizzling your fluid if your not careful. Flat plate has surface area on it's side and dealable (sp) high limit temps in the collector. If it is a drain back then you are heating storage temps immediately and only one exchange for SDHW.

(EDIT) The caveat for all of this is the fact that you need to look at is "system efficiency". If an evac can go to 400*F.... so what. What I am looking at is what temp and how quick do my loads go to?

I thought Oventrop had a drain-back evac tube of sorts around for a while?

I have yet to see on the residential side of things where an evac tube system is a better fit than a flat plate in Colorado. Maybe in lower sun areas but I even question some of the numbers that have been claimed. I think some of testing needs to be done (or redone) for comparison.

Drain back, flat plate, stainless steel storage tanks.... that's the way to go in my book.

Maybe it's time for the good old USA to lead the way for next generation solar thermal technology.

Metro Man

Andrew Hagen_2

Leading the way

Maybe it's time for the good old USA to lead the way for next generation solar thermal technology.

I tend to agree on that count too.

Not to discount the experience of those in Europe,but just because it has not been widely done in Europe does not mean it is not good. The ability to turn off a solar thermal system is a big advantage in my opinion. I like when systems fail to their safest state. There is very little extra complication to a drainback system, though it does cost a bit more, particularly because of the drainback tank itself. On the environmental side, there is no need for glycol which saves the impact of production and eventual disposal of this chemical.

As far as the evac tube versus flat plate argument, my opinion is that the overall performance is similar for a 30-tube heat pipe evac tube versus a 4x8 flat plate. Aperture for the evac tube is 30% greater than that of the flat plate for similar performance. Evac tubes cost a bit more (Apricus), some cost a lot more, but there is something to be said for the ability to carry one up a ladder when retrofitting a sdhw system to an existing home. Shipping and storage of evac tubes is also easier.

These statements make it sound like I think the kits I recommended above are no good. That is not true, the components in those kits are excellent. However, I do think a heat dump is necessary to prevent overheating of a glycol solar thermal system. It's the price to pay for a one-design-fits-all solar kit.

Metro Man

cost

I would argue that db solar is less costly the glycol. Take away the expansion tank, pressure gauge, check valve, fill valves, pressure relief valve, mixing block, glycol, auto air vent(s), etc... plus labor and think you'll find numbers to work very favorably for solar db.

I think when looking at engineering for solar or hydroincs, just because is has a stamp from the motherland doesn't mean it is better. They have HAD to produce a higher eff. product because of heating and fuel costs. There is good/bad everywhere. Just make sure you have the good.

Some of the very early solar heating systems anywhere came from back east and of all places.... Mass. I think there is one still operating from early, early, days. Designer used dark colored corrugated metal roofing that had some type of glazing over, pumped water from a storage tank to the top of roof and let the water run down, collected in bottom "header" and back to tank. These where called "trickle" type solar collectors. Worked great, provided all the heat and hot water to building and all they needed to do was add water from time to time.

KISS (it's not just a (USA) band)


Metro Man

hot_rod

I think there is room for both types of collectors

the evac tubes will have an important roll in solar cooling applications. Flat panels will struggle to reach the temperatures needed to drive those chillers.

There are some areas where 180F is required, dairy and ag applications need those high temperatures.

I too agree flat panels are fine for most residential sdhw applications in most areas. The evac tubes on my home do start earlier and run longer that my flat panels, and for loading nmy 500 gallon buffer I can handle 180F or more and draw my radiant down to 90F. So higher temperatures do store more useable energy.

I am becoming a db proponent They are more installer sensitive, and off the shelf components are not as available, not everyone has access to affordable custon ss tanks. We will get there on the db systems, the market is just starting to see the advantages and understanding the concept and design criteria.

hr

scott markle_2

Yes, closed loop glycol systems are vulnerable to summer power failure stagnation. But if storage is sized to accommodate summer insolation, these systems make a lot of sense. Insulated pump-stations and insulated flexible line sets are a great concept too. The more modular and easy to instal the better.

Drain back is great and I appreciate the skill that goes into the careful pipe work that is required, certainly for higher solar fractions it's very important to be able to shut things down when we have enough. Still I would argue that a collector thats not pulling heat on a hot august day is missing out on it's best payback conditions. The more time spent collecting energy the sooner it's embodied energy will be recovered.

Small is beautiful, if we have to open the check valves to allow some night time re-radiation on a small closed loop system while we are on summer vacation, if we even have to do a bit of pumping to accomplish this, it probably adds up to less than the extra pumping required to prime a drain back system.

As far as Kiss is concerned I think this is the beauty of small closed loop systems.

Mark Custis

Scott

Nicely said.

I discovered Wilo here in Cleveburg summer of 2007 at the International Solar show. I had to go home and change underwear when I saw their 32 VDC pumps. Variable by nature of DC.

The space station works so well because they are not inverting and deverting power. They built it to be run by the collecters.

Metro Man

E-Fish-Aunt

When we do real comparisons if using a mixing block with dual pumps then closed loop system power consumption is about the same as what is required with drain back higher head pumps.

I do like var. speed pumping and working with a solution for drain back systems. Wilo had something going on but think they backed off due to the freeze potential. Still would like to see a Wilo pump w/ external sensing for delta T & P.

As far as sizing solar storage tanks vrs. coll area. There will always be a point at which the tank will hit high limit temps. Waiting until evening may not be soon enough. But..... properly sized, these systems should to be able to take whatever temps and pressures the system will ever see. I think this is the strategy one should follow when designing a closed loop glycol system and not rely on some thing to switch on or off to prevent something bad from happening.

In the last 5 years or so we have seen the square footage of collector array come down in relation to the size of the home. This is mainly due from tighter homes and better heating distribution installation practices.

Just finished a 6500 sq ft home using 240 sq ft of collector area. Home has been heating all winter (while under construction, doors windows open at times) with solar and small backup of boiler. 10 years ago we may have used 1.5 times the collector area. Yes it will idle some in the summer months. But the spring, fall and winter energy displacement is worth it.

But.... it's all good as long as you put some thought into your design.

I think Larry has the right idea.... use Vodka. Would rather bring in 55 gallon drums of Kettle One instead of Dow frost.

Metro Man

scott markle_2

Question: for HR, If I had a 75 gallons pre-heat tank and two caleffi flat panels in a ideal site at 40deg. latitude, panels @ 45 deg. pitch, day time ambient 80 deg., night time ambient 68deg.

10 cloudless days (and nights) in july

Can you tell me if I can keep my glycol below 185, with constant circ. in this almost impossible condition, (not asking for any calculation of tank and line losses.) what do you think? I'm guessing it's stagnation proof. but I'd like to know if this can be calculated with more than guess work.

62,550 btus to raise 75 gallons 100 degrees (8.34x75x100) lets say we could average 8kbtu/hr for an ideal day. Thats 7.8 hours to go from 80 to 180. But the efficiency of the collector falls off as our tank temperature gets hotter, tank and line losses also go up. seems like a complicate thing to model

At night it's turned around and the collector will make a fairly good radiator W/ 180 water and a clear sky. Does any of the solar software model this sort of thing, do flat plate manufactures provide any information on the efficiency of there collectors as night sky radiators?

rene_4

I got to thinking about power failure and what it would do to my closed loop system if I was gone several days. First of all, I plan on leaving my check valve open to have gravity circulation work for me at night in case of overhearing. Then I happened to think. I burn wood pellets to heat my house all winter here in New Hampshire. All the fans and blowers on the stove use 110 volts. In case of a power failure during the winter, I installed a power converter which converts 12 volts DC to 110 volts AC. I have two deep cycle batteries hooked up to it. They came out of my RV. Last December, we had a huge ice storm. I lost power for 5 days. This battery backup ran my stove for well over 24 hours. So then I thought, why not hook it up to my solar system in case of power failure during the summer especially if I was gone for a couple of days. Works for me. No more worries. I'm going to have to do a test to see how long my circulator will run using 2 deep cycle batteries.

One other thing maybe someone can answer. I have a three speed circulator. Does anyone know if it's more eficient to run it on high, medium or low speed to get the most out the system. I have two 25 evac tube collectors and a 80 gallon storage tank. Thanks.

Rene

Mad Dog_2

Great posts...........Question for the solar Gods......

In the absence of a good dump zone, i.e., a pool...could a long copper coil buried in the ground suffice to dissipate heat? someone mentioned PEX, but copper is a much better conductor. Mad Dog

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Unknown

Right on the money

The drainback system simply eliminates all those problems. That little percholating sound you hear in the drainback tank, well thats just the sweet sound of free money.

joel_19

Yes

Sure you could put the heat in the ground. Now think about this what if you had that in the center of a direct exchange Geo thermal field. Spring/fall you could still be overheating your domestic tank dump the heat in the ground and suck it back into the house via the geo.

FYI we have done both flat and Vac tube. Without a doubt in our climate the vac tube outperforms the flat. I have cleints heating 80 gallon tanks to 90+f on 5-10f days with 1 30 tube collector. They start heating much earlier in the morning an extra hr or 2 is a big difference when you only get 8hrs of sunlight in a day.

We are using a high end German heatpipe collector. I am concerned about all these cheap made vac tubes thier performance and lifespan might not be very good compared to a standard flat panel. If it was a choice of cheap vac tube versus high quality flat i would always err towards quality.

Unknown

Sun maxx

vac tubes work well with drainback, straight 1" manifold with heat tube wells entering from bottom, have mine set at 16 to the foot which is unnoticable with roof line and drains well.

Mark Eatherton

My issues with drain back solar...

Worse case scenario: Middle of summer, system maxes out storage tank by 11:00AM. System shuts down based on high limit and drains back. Collectors stagnate, sitting at 350 degrees F. Consumer comes home and uses large quantity of hot water. Drops storage tank temp below high limit. Differential controller starts pump back up on solar loop. Sounds as if Boing 747 has landed on the roof of the home. Homeowner gets on phone and calls installer and wants to know WTFO?

In severe cases, collectors become vapor locked, and water doesn't over come the steam pressure and adds to the steam flash condition occurring on the roof. No additional energy is harvested off roof.

With that said, does anyone have a reasonable solution to THAT problem? Not being familiar with all that Resol controls have to offer, is there a cycle that WON"T allow the 747 to land on the roof?

Am going to be installing my own drain back system this week and will document it via digital photography.

TIA

ME

hot_rod

pressurized drainback is the way to go, this letter

is from a high altitude drainback owner. He was having a lot of the banging noise you talk about.

The response from Dale at Radiant Engineering is right on. You need to know about lift, boiling temperature, pressures, pump curves, pipe sizing, etc to design and build a trouble and noise free DB system.

Attachment picture 13, thanks to Siggy shows how the dual pumps behave and how the operating point shifts in a DB piping system.

Really the collector shouldn't see well water temperatures? If the homeowner uses a large amount of hw the pump should kick back on based on the 12 degree delta t in the control. So if the setpoint is 140F, although higher is a consideration, then the panel should never see colder than 12F below setpoint. Still a huge delta t, no doubt.

I've heard there are some collector manufactures that don't reccomend their collectors for DB due to this thermal shock condition.

I think with DB it is important to get the collector sensor mounted to the absorber, not in a well or on the piping outside the collector box. This may require cutting access in the back of the collector.

The DB specific controls do have some special and unique features worth looking into.

Here is the response letter, picture 11 to a perlexed DB owner.

hr

Metro Man

Big Bang theory

Mark, I have never really had any problems with any of my drain back with what you describe. I kinda like the boeing sound and have a display on a trailer that we do it all the time. I'll let coll plate got to max (350 ish) and let 'er rip. Your right it makes all kinds of noise but will soon settle down. Have never had a system flash so bad that it stopped flow.

It really is a non issue on most of our systems because you would have to go through lots of hot water. 1000 gallon tank HL's at 180*F and you start drawing off energy for 140*F dhw load. Would have to go through quite a bit of hot water to start things back up but guess there may be a time. Thing w/homeowner is to show them when commissioning system.

Probably the bigger issue is power outage then everything comes on line but... still never have had issues or complaints. To be quite honest we never hear from our drain back clients but do from out glycol. In another month or 2 is when we get busiest..... things start to heat up and the weak links in these system will show they're face.

We use a steca controller that has a pump protection setting that we will sometimes activated. Set for 40* over high limit setting of tank. Remember the water going to absorber plate is hot during these conditions.

BTW - where are you installing?

Metro Man

Metro Man

yo HR

If DB homeowner is still perplexed in CO Springs, have them call me. Will see if I can help. I have many large DB systems at 8000'.

Dave, Metro Solar Inc. 866-782-9099

Metro Man

Mark Eatherton

Top SECRET location....

I could tell you, but if I did, I'd have to cut off your fingers and whack off your tongue so you couldn't tell anyone else :-)

Am not taking out any stinkin' permits, and am not asking for any tax subsidies...

I just want to use solar hot water so I can take a longer shower and not feel guilty about it :-)

Once you've read the above statement, you can probably figure out where the project is...

Thanks to all for their responses. I will tell the HO to "get over it".

ME

Metro Man

Big brother

Watch out Big brother is listening..... Joe inspected may pop out behind a pine tree and red tag ya.

Let me know if you need anything for the cause..... have quite a bit of used equipment.

BTW - I keep wondering what side of the water your on when driving by? Highway side or residential side. Saw you curly cue pine tree pic on an earlier post.

Metro Man

Metro Man

tube

Whatever you do don't use pex..... you'll melt it. Think I would just save my money and buy a bigger expansion tank. If you have evacs maybe turn some away from sun or cover. Flat plates..... no worries.

Metro Man

Mark Eatherton

Teeney Weeney Heeney

I've dubbed myself a Heeney Hillbilly because the county does not recognize us as even being in existence due to lack of sales tax base. Oh, THAT part of the county..."

You'll have to stop by and see me some time.

And thanks for the material offer. I've pretty much rounded up everything I need at this point. Collectors are already up, storage tank is already down, just need to run pipes and wires in between and fill and fire.

ME

Metro Man

Green Mnt Res

Pass by every time I drive to Steamboat..... wife caught her 1st fish there years ago. Still remember her apologizing to the poor trout as she de-headed it. Funny thing was she had drag set so loose the fish was taking line until she just grabbed reel and walked backwards up shore with the fish a-flappin. Good thing Mr. Trout swallowed the hook.

Doesn't the blue flow diff. directions at diff times of the year? Thought I had heard that when Res is low or high dictates???

Nice area. Have friends that used to Kayak the Green. Want to take the road to state bridge on day.

Have fun firing up your db system.

Metro Man

scott markle_2

Most closed loop solar designs don't require very high flow rates. If you have a flow meter on your system and speed 1 will achieve enough flow then thats were it should be set, Collector delta does effect efficiency and this is directly related to flow, higher flow would mean a lower average collector surface temperature and higher efficiency but maybe if we have an already high tank temperature we would want to slow things down on the collector side to increase the contact time in the collector and get reasonable delta.

Perhaps some of the experts here could give you a rule of thumb on flow rate/surface area of collector.

Andrew Hagen_2

Waste heat

My take on the issue is that ideally the time the array is turned off is short, so there would be very little energy to dump. If the system has to dump a lot of heat, either the array is oversized or the storage is undersized.

Mike C._4

System sizing issues

My issue with system sizing is that it is based on a certain amount of hot water useage. If you don't use the water then that will need to be addressed. I have 105 evacuated tubes installed and only intially had 160 gallons of storage. Before I activated the overheat protection mode in the Resol controller I had a spike in collector temp of 237 deg for a short time. Doesn't take long. The overheat mode will override the 165 deg tank temp to a point and "bump" the pump every 15 min or so. I went away for 48 hours and the collectors did hit the 275 deg shutdown temp first week of February with cold temps. No relief valve burst. No system problems. I didn't think the sun was going to be an issue but it was. I had planned on heat storage/radiant tubing but didn't get it going at that time. I have since installed a Modine fan heater for a temporary dump to my basement. Basically like this: http://solarthermal.com/Applications/application14.asp. It is all automatic and works like a champ. I think I may keep it permanently. Next will be to add the dump to my pool heat exchanger. Almost done. Last, I will install a UPS backup for the collector pump and Modine heater. I have had the tubes literally half buried in snow and they were still working great.

Mike C

hot_rod

not too slow, as the \"linger\" time

will drive up the collector temperature and along with it the loss to ambient.
Shot for about a 10 degree delta t across the panels. depending on the type and size of panel generally around 1 gpm per panel. The panel manufacturer should have the test flow data, as does the SRCC sheet.

With swimming pool mat panels they tell me 5 degree delta T, due to loss without insulation or coverings.

hr

Metro Man

flow rate

Flow rates depend on length of plumbing, load your heating and collector type. A 4 x 8 flat panel typ. has a flow rate of .75 gpm recommended. But if the thing is a mile away from the storage tank then you may want to slow things down.

We shoot for a 15 delta between the load and collector. Big thing is to keep things from short cycling. Flip side is you don't want too high delta because as load temps reach HL then you may be running excess.

I don't look to careful at the efficiency of the collector (yes it is more eff. when running cooler fluid temps) as much as the entire system eff. and what I am displacing. Would rather run solar below it's eff. potential than running backup.

A pool or hot tub you want closer just because you don't want to burn anybody who may be next to a jet when system is running.

Metro Man