Does Pre-assembled pump station make sense?

CallaW

Hi All, This is RyanW's brother and wife, we are also designing our own solar thermal system. We are doing a ground mount, because we don't have enough room on our roof. So we can't do drainback. We also have a radiant floor, but we have room for a large storage tank (500gallons), so we are planning on a large flat plate array (240-320 sq ft) with a closed loop antifreeze system. Because of summer overheating concerns (Central VA) we plan to have the array at about 75 degree slope.

We are seriously considering the pre-assembled pump station by SolarHot- SolVelox (the commercial one). Anyone have any opinions on these particular products? or know if there is a better one? we like the fact that it is pre-assembled and includes a heat exchanger.  NathanW is currently finishing the drawings and we will post them soon. Any advice you all have would be greatly appreciated! 

CallaW

drawings

Here is our drawing... would love recommendations on high efficiency pump and size for this very simple radiant floor system. any feedback on the heat dump system?



Is using an instant hot water heater in this configuration feasible for DHW backup?



anybody used a plastic tank such as this?



Currently we heat with wood, and plan to continue this in the future.. Therefore, we envision using the radiant floor only when the sun allows. However, we want some ECONOMICAL backup for the radiant. Anyone think a 40kBtu gas hot water heater fits the bill?



Thanks in advance!

hot_rod

a couple thoughts

a plastic tank that can handle 200F??



If you are building that coil for DHW consider 3 coils of 1/2" copper 60 foot long, headered together. Less pressure drop and more heat surface area, if in fact that is a 180' loop of 3/4"?



Consider a solar control that would not require you to manually switch from solar to backup source. Most controllers have a output to run a 3 way diverting valve to do that for you, based on useable temperature inn the tank.



Also maybe a combo boiler/ DHW boiler or heater, better to have a high efficiency 90% boiler to provide backup heat and DHW, all in one package. Plenty of good brands to chose from. I'm not a fan of tank style water heaters for radiant heat sources. Unless it is a high efficiency condensing unit.



Yes, a packaged pump station is a good way to go. It should include all the correct valves and pieces, rated for solar temperatures.



hr

Kevin_in_Denver_2

Heat dump unecessary

Steamback is the new way to eliminate heat dumping, which is spending money to waste energy.



Here’s John Siegenthaler’s explanation of the strategy:

http://www.pmengineer.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000570238



And a lengthy discussion of the pros and cons:

http://www.heatinghelp.com/forum-thread/133064/Steamback-System-Design

CallaW

Thanks Hot Rod!

Thanks HotRod,

I've adjusted the drawing to include the (3) 60' 1/2 copper coils in parallel. That makes much more sense! I'll think about using one heat source for both. The instant hot water heater I was thinking about is condensing, they advertise 98% efficiency, but I don't know what the Navien would do with 100-110 deg. water coming into it. I've heard this can cause some instant water heaters a headache.



anyone know of an American made condensing instant water heater that might work in this application? whatever the heat source, we'd like to spend less than 2K.



we are looking at other tank options, as i've heard elsewhere these polypropylene tanks get soft above 160deg even though this manufacture says its good for constant use up to 190. Go figure. Any suggestions on a tall and thin tank that would stratify heat well?





Thanks!

nathan and calla

CallaW

Steamback

Wow, now its even more clear why this is best left to the professionals. We will do our homework (thanks so much for the links!) plug in the numbers and see what size expansion tank is called for.  I feel like I'm back in college! 



Seriously, I really like this solution because it requires no moving motors, works when the power goes out, etc.  THANK YOU!

hot_rod

tanks

if you are looking for open tanks, Tom has spent a lifetime perfecting his design. He knows what type of materials do and don't hold up.



www.americansolartechnics.com



I've tried HDPE tanks and they really don't hold together well when the get soft from high temperatures.







For closed pressurizes tanks many of the wood boiler folks use LP tanks. I have seen them mounted vertically in a truck rim. Tough tom get internal coils in them you would need to wrap externally or use a plate type HX.



www.ahona.com



Insulated, pressurized Tanks over 120 gallons, may require ASME listing and get fairly $$. 10- 12 bucks a gallon is common for large, insulated, listed storage tanks.



hr

CallaW

tall tank??

So how much does a tall thin tank matter? I've heard its important for stratification?  If we have a square tank that is say 60" x 60" by 50" tall and another tank that is 50" diam and 100" tall (those numbers are not precise, lets say both factoring insulation could hold 500 gallons) is the taller thinner one always going to make the flat plate solar panels perform better? 10% better? just a few percent?  The solar panels would be heating this tank via an external flat plate head exchanger.....



Just trying to get my head around this!



Thanks,

Nathan

Karl_Northwind

heaters.

I haven't had time to respond in as much detail as I would like, but I will recommend a using a high efficiency tank style water heater  (I would use the aosmith vertex GDHE50)

and use a flatplate heat exchanger to go from there to the radiant floor system (as long as you can use under 140F water for your radiant system.



this will provide DHW and space heating in a single appliance, have large buffering capacity and with proper controls allow you to have outdoor reset and such.  and when it finally craps out (in a long time) you can be certain that there will be something hydraulically equivalent to replace it with, not some fancy boiler that will require a whole bunch of near boiler piping to make it work right with your heating setup.



Caveat: this is dependant on not having hard water, or having a water softner pre-heater.  using open source on the heater surfaces with hard water isn't good in the long term.



as your panels will be ground mounted, you could pretty easily just cover half of them during the non heating season.  I'm curious about the steamback principals, but haven't ever dealt with them.

CallaW

Heaters

Hi Karl,

Thanks for the feedback. Is it your experience that instant hot water heaters (assuming condensing and thus hi efficiency) don't work well with pre-heated water?



Nevertheless, I like that AO Smith heater, and I've asked for a price on it from our local dealer.



Do you have an opinion on tank geometry? We are wondering if short and squat is OK for this kind of setup.



Thanks for the help,

Nathan and Calla

ABSolar

Final check

Hi CallaW,

One final check - are you absolutely SURE you can't get the pitch needed for drainback or did you just assume because its a groundrack setup?  If the ground rack is 2'-0" above the grade, and grade is, say 6' above basement floor, and you keep the groundrack close to the house, then you could do drainback.  It sure would solve your overheat issues if you can get 320 sqr ft of collector to safely turn off in the summer. 

That being said, if you still have to do glycol, and you're planning on steamback as your emergency back-up, then be sure to SUPER SIZE your expansion tank!  Especially w/ that many collectors.  By the way, heat dumps are only good as long as there's electricity to power the pump, controller and diverter valve.  But if the power goes out in the summer during the daytime, you'll be spewing glycol...probably should plan on covering all but 2 collectors after the heating season is over (since it's a ground rack, you have easy access)

ABSolar

On demand hot water heater

Hi CallaW,

If you decide to use any on demand hot water heaters (gas or electric), you must make certain that the unit is of the modulating output type that vary the the combustion burner rate based on supply water temp.  Otherwise the unit will short cycle, on, off, on, off trying to boost the water temp from say,  solar preheat temp  of 105 degrees to 130 (which they will do, because they will reach satisfied output temp. condition quite rapidly).

That being said, I like HR's suggestion of one combined condensing burner to do double duty of backup domestic and backup radiant heating.  My bid would be using a Triangle Tube Prestige 60 assuming the radiant panel field load isn't too big...

Karl_Northwind

heater

I think short and squat is adequate for most setups, as long as it's not a tank with other heat sources in it.  tall and skinny is great for single tank DHW systems, or other systems where there is heat introduced from multiple sources.



I have zero experience with tankless heaters with preheated water, but tankless to my mind, I would expect to be more trouble prone than tank style heaters. 

the slick thing about the tank style heater, described above, is there will always be something to replace it down the road.  I would expect that heater to be cheaper than a condensing tankless and a cheapo power vent water heater.  and have less moving parts and higher efficiences than both.



I have exactly the setup I described heating my house.  I have 2 temps, one up and one basement, 4 zones (soon to be 6 zones) outdoor reset on all but the basement floor (runs with the upstairs temps and is high limited to 100F by a dumb Thermostatic mixing valve.)   No solar integrated yet, but will be in time for summer. 



I need to get around to posting a schematic on here to get feedback.  there are a couple of things i would do differently, but it's running like a champ.



karl