Best passive SHW opinions?

[lark]

Hi all
Feeling pretty stymied here. It appears there are only 2 sellers in US for evacuated passive SHW systems, Dudadiesel and Solarbank. Seems like a few different makers of tubes like Apricus, thermomax etc. but all going in to active systems with pumps. And seen many problems listed here with those makers anyway.

Duda uses salt water in the heat rod and rated to 14F. Solarbank is like 600 bucks more, OUCH! but uses copper powder/water mix and rated to neg 35F. Do need something would go pretty cold but 14F Duda is okay. Thing is, quality unknown in other ways with either brand. Absolutely minimal risk of long term problems is the goal here like coatings decaying or slow vacuum leaks.

Apparently even in best system air does permeate glass with expansion contraction of heat/cooling but don't know what that rate is if anyone could comment. A 10% vacuum loss or coating decay in in 25 years say like a pv panel would be okay.

The angle on this question, my main concern, is poor workmanship or design.

Anybody else? what should I do? Whole industry seems untogether imo. Really have to work to get info and can't trust that. Undisclosed China makers etc. I know, move to China and buy from the local hardware store who's owner buys eggs from you.

Solarbank doesn't seem to have certification. Manual is a lot better though, which shows diligence.

Second choice is get a flatplate collector and drain in winter plus put up with less efficiency. At least wouldn't have vacuum or coating problems in 5-10 years. But they are scarce also so any recommendations who?

ET sure is tempting if just look at specs unless one has real sunny winters.

What happened? Seems like more choices few years ago. Doesn't mean quality was there of course

This post keeps screwing up, repeating sentences and can't edit.

Thanks

[Mike90250]

I have a passive Rheem solar hot water system. It's a flat plate glycol collector, with an integral storage tank above the collector. Bought and installed in California

[russ]

Look at this site http://www.fsec.ucf.edu/en/certifica...rmal/index.htm

There are plenty of systems available. Vacuum tube types are not required or beneficial unless you live in the cold north.

For hot water for the home the heat pump style hot water heaters are more economical at this time.

[lark]

I have a passive Rheem solar hot water system. It's a flat plate glycol collector, with an integral storage tank above the collector. Bought and installed in California

Hi Mike,

That's a pretty interesting setup you have, thoughi don't see Rheem or anybody offering that now. I guess the glycol must travel by thermosyphon into a heat exchanger in the tank. I'm in southern Oregon so pretty close to you and would probably like a system like yours and would just drain external pipes when freezes. Do you do that?

Understand glycol can be a problem in summers if overheats. Have you had any issues with this and do you deal with it by just using lots of heated water?

[J.P.M.]

Hi Mike,

That's a pretty interesting setup you have, thoughi don't see Rheem or anybody offering that now. I guess the glycol must travel by thermosyphon into a heat exchanger in the tank. I'm in southern Oregon so pretty close to you and would probably like a system like yours and would just drain external pipes when freezes. Do you do that?

Understand glycol can be a problem in summers if overheats. Have you had any issues with this and do you deal with it by just using lots of heated water?

FWIW, there are lots of passive DHW systems available, batch, flatplate, breadbox and variations.

Glycol of most any type may be a problem if it overheats and/or if the ph isn't monitored and the glycol isn't changed out as needed. Sometimes stagnation conditions on very warm, and/or very sunny days can occur, particularly if flow is somehow restricted, and if the glycol loop pressure is low. In such cases, the system pressure relieving devices will hopefully operate, probably dumping glycol/H2O, which BTW, if (hopefully not) ethylene glycol, is toxic to some animals, house cats included. Propylene glycol is usually what's recommended or DWH closed loop systems.

[lark]

Look at this site http://www.fsec.ucf.edu/en/certifica...rmal/index.htm

There are plenty of systems available. Vacuum tube types are not required or beneficial unless you live in the cold north.

For hot water for the home the heat pump style hot water heaters are more economical at this time.

Thanks for that link, Russ. I had not realized that there was an alternate rating agency to the SRCC. what advantages do you find to using the FSEC? At first glance it seems not as inclusive. For instance if you plug in Jiangsu under collectors you only get one entry instead of a whole page with SRCC.

Well, as you know, the "cold north" where it can freeze and bust collector includes most of US and Canada. In moderate areas one can drain the supply lines or fix them if forget(and we are willing to do that) but can't risk panel damage.

Thing is, need simplicity/maximum durability. Want to avoid pumps, even direct pv panel driven ones so that removed all the alternatives, excepting Mike's example maybe, if could find. Hence the seductive power of EV but currently skeptical.

Off grid so wasn't too attracted to heat pumps at first. Seems nuts but just got tuned into idea of direct pv into the tank elements. Seems like might work if use the right element. Example---at 48 volts a 120 volt element would consume 4 x the power as a 240 volt element..

As long as use dc thermostat and can afford 5 x more space lost on roof as opposed to thermal collectors and panels are .65/watt why not? Could even set up separate system, apart from house system if one chose. Simpler, cheaper, and more bomb proof. Or maybe not, you're the expert.

Find very scant mention of anyone doing this in an off grid way.

But I'm digressing, sorry

--- Mod Note: display of this post was delayed by the requirement for moderation that was apparently triggered by the presence of the link.

[Mike90250]

The Rheem I have, has the collector below the storage tank, and is thermosiphon powered. They glycol is freeze resistant. The storage tank has a 180F pop-off thermal valve that dumps hot water onto the roof, and is replenished with cold tap water, so overheat is a non-issue. (as long as the valve is working). So it's pretty bomb proof. Don't know why it's not showing up anymore.

page 4

http://cdn.globalimageserver.com/fetchdocument-rh.aspx?name=solpak-featuring-a-gas-assist-heat-exchange-tank-rheem-solar-solution-brochure

Solaraide passive water heating systems are available in 47 and 80-gallon storage capacities.

Has a 240VAC electric emergency backup, which is not used on mine, I feed mine preheated water (about 90 - 100 F) from my wood heater.

[LucMan]

Hi all
Feeling pretty stymied here. It appears there are only 2 sellers in US for evacuated passive SHW systems, Dudadiesel and Solarbank. Seems like a few different makers of tubes like Apricus, thermomax etc. but all going in to active systems with pumps. And seen many problems listed here with those makers anyway.

Duda uses salt water in the heat rod and rated to 14F. Solarbank is like 600 bucks more, OUCH! but uses copper powder/water mix and rated to neg 35F. Do need something would go pretty cold but 14F Duda is okay. Thing is, quality unknown in other ways with either brand. Absolutely minimal risk of long term problems is the goal here like coatings decaying or slow vacuum leaks.

Apparently even in best system air does permeate glass with expansion contraction of heat/cooling but don't know what that rate is if anyone could comment. A 10% vacuum loss or coating decay in in 25 years say like a pv panel would be okay.

The angle on this question, my main concern, is poor workmanship or design.

Anybody else? what should I do? Whole industry seems untogether imo. Really have to work to get info and can't trust that. Undisclosed China makers etc. I know, move to China and buy from the local hardware store who's owner buys eggs from you.

Solarbank doesn't seem to have certification. Manual is a lot better though, which shows diligence.

Second choice is get a flatplate collector and drain in winter plus put up with less efficiency. At least wouldn't have vacuum or coating problems in 5-10 years. But they are scarce also so any recommendations who?

ET sure is tempting if just look at specs unless one has real sunny winters.

What happened? Seems like more choices few years ago. Doesn't mean quality was there of course

This post keeps screwing up, repeating sentences and can't edit.

Thanks

Drainback system with flat plates best way to go in my opinion.
You may lose a slight amount of efficiency but the longevity and lack of required maintainance make up for it.
There are still many of these systems operating today that were installed in the 70's.

[MikeSolar]

I've put in many, many thermosyphon systems (passive is not a good term for it). Almost all the American made collectors are grid type and are drainback-able and therefore can be used as a thermosyphon. A normal glass lined or SS tank can be used, and not too much else is needed, just piping. Lots of good diagrams out there to go by. Get out the torch and wrenches, haha. (just don't use any PEX tubing, BTW)

[lark]

The Rheem I have, has the collector below the storage tank, and is thermosiphon powered. They glycol is freeze resistant. The storage tank has a 180F pop-off thermal valve that dumps hot water onto the roof, and is replenished with cold tap water, so overheat is a non-issue. (as long as the valve is working). So it's pretty bomb proof. Don't know why it's not showing up anymore.

page 4

http://cdn.globalimageserver.com/fetchdocument-rh.aspx?name=solpak-featuring-a-gas-assist-heat-exchange-tank-rheem-solar-solution-brochure

Has a 240VAC electric emergency backup, which is not used on mine, I feed mine preheated water (about 90 - 100 F) from my wood heater.

Many thanks for that globalimageserver link to the Rheem Mike. Never would have seen it without yah, since Rheem hides it so successfully. Curious of course how many years you've used this without problems. thinking about going this route. Maybe build a frame for it on ground (wish they sold one) so easier and cheaper to replace input pipes if forget to drain them when it freezes.

First I've got to find time to search forum for opinions on the pv direct method I commented on to Russ. Otherwise start a thread on it if necessary. Thinking there's something wrong with it besides taking more space but not sure what yet. Read something vaque awhile back about mppt and pv direct that made no sense but i'll get to it hopefully.

[Mike90250]

I've used it for 2 + years now. No issues. The connector pipes are some sort of corrugated SS with an insulating shell. Supposed to withstand freezing. Collector & tank have never frozen, the connection pipes froze once, and thawed fine.

in winter, sunny days, I get 100F water out of it, which is nicely preheated for my tankless propane heater to finish off. Summer, I get over 130F, and my mixer valve thins it down to 115F and the tankless hardly does a thing .

[MikeSolar]

I've used it for 2 + years now. No issues. The connector pipes are some sort of corrugated SS with an insulating shell. Supposed to withstand freezing. Collector & tank have never frozen, the connection pipes froze once, and thawed fine.

in winter, sunny days, I get 100F water out of it, which is nicely preheated for my tankless propane heater to finish off. Summer, I get over 130F, and my mixer valve thins it down to 115F and the tankless hardly does a thing .

Yes, I've brought over a lot of the stuff from Germany and Turkey (Torgen and aeroline) and it is very good for all types of systems. I wouldn't rely on it for much freeze protection, at least where I am and -35C temps. Most of the thermosyphon systems we use here are for 3 season applications like cottages where they can be drained in October and refilled in april. There are some where we pit the tank (with HX) in a conditioned attic above the collector and fill the collector with glycol. They can work well but not every house can do it.