Solar water preheater project based on builditsolar $1000 system

[strider3700]

Originally Posted by Piwoslaw

Unless you find laws which state that your heat exchanger must not only be double walled, but also certified, then you can try to make your own. For example, instead of making an open solar loop that dumps into the non-pressurized tank, make the solar loop closed and use that tank as the double walled heat exchanger, something like a heat buffer. That way you can use glycol in the solar loop (to prevent freezing) and still keep it two walls away from your city water.

If you want/need to keep the solar loop open, then get a hot water tank with a (single walled) heat exchanger loop inside and hook that up to the loop in the non-pressurized tank.

Or go a step further and replace your hot water tank with a heat buffer. It should be a tank with two coils - one for input, one for output - while the tank itself and all of its water only act as heat storage (and as double walled heat exchanger).

I've been told the US requirements for double wall heat exchangers state that there must be 2 metal walls between any heat transfer fluids so your cases wouldn't work because the fluid in the tank between the two coils could contaminate and then contaminte the other coil should both spring a leak at the same time. Totally insane I know but still the law... no wonder noone cares about the rules in most cases.

[Piwoslaw]

WOW! You're serious about this. Good for you!

Originally Posted by strider3700

In the end he took all of my printouts and said he'd do some research but it would take awhile.

I wouldn't be surprised if it took him until the new, double-walled F379 came out

Originally Posted by strider3700

I've been told the US requirements for double wall heat exchangers state that there must be 2 metal walls between any heat transfer fluids so your cases wouldn't work because the fluid in the tank between the two coils could contaminate and then contaminte the other coil should both spring a leak at the same time. Totally insane I know but still the law... no wonder noone cares about the rules in most cases.

The problem with '2 metal walls between any heat transfer fluids' is that it's so darned inefficient, not to mention more expensive.

If one of the walls in a double-walled heat exchanger corrodes, then no-one will notice (except for the HX's efficiency suddenly rising since it is now only single-walled). But in the system I proposed there is a greater chance of noticing contamination of the intermediate fluid before there are breaches in the heat exchangers on both ends. But, as we all know, law has more in common with politics and lobbies than with common sense...

[strider3700]

Right now the math suggests I'll save about $1050 over 5 years and $11,050 over 25 if the current rate of inflation on my electric bills keep happening. Even if I have to buy a commercial heat exchanger and add 2 more pumps I will be doing this. If I can get away with the single wall exchanger then my system should cost me about $1200 with half of it already purchased. if I need to go double wall flat plate add at least $1000 if I build my own double wall with air gap think coils wrapped around a central tube I think I can do it for only $500ish.

If I need to I'll say **** the permit.

So yeah I will be doing this period.

[AirSepTech]

Your original design is the most cost effective, efficiant, and I believe safe way to solar dwh. I work with heat exchange, it's our lifeblood.

If you develop a leak in your HX, barring some un-natural force, only 2 things will happen.
1) You will have no hotwater supply/pressure.
2) Your buffer tank will flood with cold water.
Further, I fail to see a true risk to human health. Who is drinking HOT water?
It is always recommended NOT to do that.

Double wall HX do not work well. You need whatever your largest gallon demand is soaking in that HX/tank to really take advantage of your low cost system. A double wall HX that size is costly.

I to want system like this. I want to run at 70f and soak the condenser coil on a modified inverter ASHP. I will need a BIG tank.

Best of luck to ya, I have some good friends in Trial.

[strider3700]

this is a direct repost of the message on simplysolar in case anyone else is reading that --

My last update was that the inspector was going to look into the actual code that he had originally rejected based on something he heard at a conference.

Today I got a pile of paper work with the requirements including his checklist.
His check list is

1 - Panels be securely attached to the roof as per manufacturers specs
2 - heat exchanger/back flow prevention to be installed.
- Double wall heat exchanger - with leak path to atmosphere
- single wall exchanger - must meet BCBC 7.2.10.13 (which just says must meet CSA-F379.1) and a minumum of 2 RPBA's for premises isolation and cold water supply to system.

3 - Solar storage tank
- seismic restraint ( 2 straps located top and bottom 1/3 (BCBC 1.1.3.11)
- Tank on drain pan (BCBC 7.6.1.7.(9)(10)
- Temperature and pressure relief valve (BCBC 7.6.1.7.(1)(2)(3))
- relief valve discharge pipe to acceptable drain (BCBC 7.6.1.7.(1)(c))
- Air vacuum breaker(BCBC 7.6.1.7.(8))

4 - Tempering(Mixing) valve on domestic hot water supply CSA F379.1-88(7.3.1)and CSA F383-87-(7.4 & 12.1)

5 - signage and labeling.
- piping or insulation shall be identified by markings that are permanent, distinct and easily recognized (BCBC 7.7.2.1)

6 - Thermal expansion to be installed
- solar system pressure loop (CSA F383-87 (7.6.2))
- Domestic potable water system (BCBC 7.6.1.11.(1))

7 - Solar system piping to be adequately insulated CSA F383-87(10.1)

8 - Solar System requires a presure relief valve (Setting ___ Psi).CSA F383-87(7.3 & 12.2.2)
- Pressure relief valve discharge pipe approved for high temperature
- Discharge pupe to metal holding container labeled 'Non-Potable' CSA 383-87 (7.2.4)

9 - System parts to be certified and approved (BCBC 7.2)

10 - All plumbing connections completed by a qualified plumber(BCBC 7.1.4.1.(1)(a))

11 - Engineer design drawings required (B-1.B-2.C-B) At the discretion of the authority having jurisdiction


At the bottom it lists
System Installation Requirements/Good Practices
Panel Orientation - facing south as directly as possible.
Minimum of 3 shut-off valves to allow for bypass of solar heating system.
Air vent to be provided on Solar Heating System at highest elevation.
Marks and signage - refer to CSA B128.1 for directions


then on a sperate not connected page
CSA F379.1-8 allows the use of both single and double wall heat exchangers:

Drainback and Closed-loop SDHWS using a single wall heat exchanger

- require a non-toxic heat transfer fluid(inclusive of all additive) or potable water in the heat transfer loop at the time of installation. Material Safety Data Sheets (MSDS) for the specific product(s) being used may provide guidance for determining toxicity levels.
- require a heat exchange tube of stainless steel construction
- require the installation of a backflow preventer in accordance with CAN/CSA-B64.3, which is a dual check valve type, with atmospheric Port(DCAP) at the inlet to the solar hot water system
- require other safeguards such as a pressure gauge, pressure relief valve and maximum working pressure as specified in CAN/CSA-F379.1-88

Double wall heat exchanger

- require the use of a heat transfer fluid that is non-toxic, or toxic with a gosselin toxicity rating of 2 or less (inclusive of all additives)
- do not require use of a backflow preventer unless a make-up water connection is provided to the heat transfer loop
- require other safeguards such as a pressure gauge and a visible means of leak detection as specified in CAN/CSA-F379.1-88

BCBC requirements: The current BCBC does not require and additional safeguards for SDHWS beyond those required by the CSA standards, unless a make-up water connection is made directly to the solar heat transfer loop.

If a direct connect is made to provide make-up water to a solar heat transfer loop that contains anything other than potable water, this direct connection should be protected in accordance with Section 7.6.2 of the BCBC


the insector also pointed out that the backflow preventers need to be tested yearly.

So the big difference between this and the 1k system is the stainless heat exchanger requirement. The inspector suggested that the dual check valve back flow preventors are not going to be cheap plus the testing requirement and figured dual wall would be cheaper.

At this point I'm leaning towards a small 10-20 gallon stainless preheat tank with a stainless single wall coil built in it then pump the solar fluid through the coil. That is likely to be easier to get ok'd and cheaper then a giant stainless coil. It will require a second pump or a 3 way valve to turn off the connection to the panels and then just use the orignal pump. That seems finiky in my mind but be the better choice. Really the pc cooling pumps are only $70 so it's probably worth just spending the money on that.

Anyways at this point I'm looking for any advice on which way to go. I know I can order a stainless tank like this online but I can probably get one made locally and at least save the shipping. I'll have to look around and find pricing then ask the inspector.

Bottom line, - Don't accept no for an answer on this stuff. The city didn't do it's initial legwork and I almost walked away from the project because of it.

[mrd]

Wow, you can only use a stainless steel exchanger. These code bodies are mindless, and legislators are mindless for continuing to adopt their measures. Who decided citizens should be legally forced to only build something if it will last forever? That is foolish in so many ways.

I can't comment on your pending decision; I just wanted to add some code references for any readers in the US who may be worried about heat exchanger requirements. I have a few versions of code available to me.

The 2006 International Plumbing Code:

608.16.3 Heat exchangers
Heat exchangers utilizing an essentially toxic transfer fluid shall be separated from the potable water by double-wall construction. An air gap open to the atmosphere shall be provided between the two walls. Heat exchangers utilizing an essentially nontoxic transfer fluid shall be permitted to be of single-wall construction.

This language is identical to P2902.5.2 of the 2009 International Residential Code.

[strider3700]

Today I spoke with a plumbing wholesaler and got some pricing. the backflow preventer's that I need by code if I go single wall are watts 009's and he has them in his system at $266 each. I can find them in the US online for $150 each but that's still $300 plus shipping and duty and taxes. The heat exchange tank that is showing up online as the most reasonable stainless single wall tank is the triangle tube smart 30. It's basically a tank in a tank and it's only $1575+tax to get it here... online once again it's $900 plus shipping and tax and duty... This is making me think dual wall once again simply because the system is rigged to force it.

I see that rheem sells tanks with dual wall internal coils and a built in electric element meaning I wouldn't need to buy a separate hotwater tank which I need to do anyways. They however are glass lined steel and have 6 year warranties. which will never achieve payback before failing. They sell a marathon line of tanks which are plastic, "inexpensive" have lifetime warranties and appear to have ports for external heat exchangers but not internal double wall exchangers. I've written them asking if they sell one with an internal heat exchanger. If not why not?

I have found stainless tanks with double wall heat exchangers in them but they are $2000 and up and don't have the electric element I would like If I'm spending serious money. there are other options but it's really looking like what I want doesn't exist without spending huge bucks. two pumps constantly circulating the solar fluid giving me 3 pumps in the system is sadly looking like the most cost effective option and I know it's a huge hit in efficiency.

It's unlikely that I can homebrew a piece that will work for this scenario and pass inspection.

All this because I may get water in my water...
That $200 coil of pex is looking really really nice right now.

[mrd]

What search criteria are you using for the dual check valves? Would these work? $50 ea.

I was also thinking, if only the exchanger tube is required to be stainless, perhaps you could use a few small short stainless pipes inside a tank of some sort, and pipe them to recirculate the fluid a bit before exiting the exchanger? The idea is to minimize the amount of expensive stainless material. Perhaps have fluid run through the pipe, and at the exit have most of it diverted through a pipe back to the intake. An inline pump in that line could control the amount of recirculation, or simply using the appropriate ratio of pipe diameters (recirc line larger than exchanger line) such that a given proportion always recirculates.. I suppose it would take some testing and ingenuity but it could possibly be affordable to do single wall. Not really sure if you could get the same bang-per-buck performance-wise as double wall..

[strider3700]

It has to be a reduced pressure backflow preventer so something like the watts 009.

I did a nice big write up yesterday but for some reason it didn't save. So here's the cliff's notes version

At this point even though the double wall heat exchangers are less efficient they are turning out to be far more economical. So the current plan is to buy a smallish double wall heat exchanger. then use the controller to turn on 2 pumps to circulate the hotwater tank through them. the el-sid pumps range from 2-3 gpm not a problem at really low watts and will meet the inspectors requirements. They are about $200-$250 online. I can use on of the swifttech mcp655 on the solar side.

According to the calculators the GEA DW4-6 is capable of taking the incoming water at 50F to 85F in one pass using pumps running at 2.1 gpm on both sides with 140F coming in on the solar side. it can then do 85-108 in another pass which is the temperature I use in the house, I'd keep circulating though and it can do 108 to 121 in another pass, one final one pass gets it to 129.

I'm pricing the marathon tanks with a backup electric heater so it will replace my existing(rusting) hotwater tank at the same time. They're plastic, and have lifetime warranties on the tanks, 6 years on the element and fittings but they can all be replaced cheaply. The one I'm looking at is 85 gallons, and has two ports on the front specifically for connecting to external heat exchangers.

Assuming I go with an 85 gallon marathon tank like I'm leaning towards that would take 2 hours 21 minutes to bring the tank right up to full heat so regular usage should only require a cycle of 40 minutes to reload the majority of the lost heat. I'll use the controller of course to cycle only based on a needed temperature gain. If It becomes an issue I can always control the electric element in the tank and delay it kicking on until the solar brings the temps up. assuming both pumps are the 20 watt pumps(that's high for the flow) then it will use 0.107 kwh of electricity which currently costs me less then 1 cent.

So right now this is looking like the way I'll be going. I can find double wall heat exchangers online that are 3 times larger for $245 but use 304 stainless the gea uses 316L and should last longer.

So much for a short update

[strider3700]

I'm going to take this opportunity to rant a little. The entire manufacturer/wholesaler/dealer system sucks. I took the hours on google to figure out what I needed, then I went to the manufacturers website and used their calculators to work out exactly what model would do it. Then when I couldn't find pricing I sent them a message asking how much? They forwarded that on to a distributor who got back to me anywhere from over night to never with most being about a week. They said go to these local businesses as we supply them. So I drove down and spoke with multiple local businesses which all said hmm yeah they're a supplier lets check the computer. Nope not in the computer ok we'll call them. So they called the distributors while I waited and the distributors turned around said they'll need to call the manufacturers and will get back to me with the price.

This happened on the GEA heat exchangers. Each person down the line was adding a nice little chunk to the price and in the end the best I got was we have a dw4-8 listed and it would be almost $500 so I said $500? the guy quickly did some math and bam $600+tax which in my mind means he just added $100 to his cost. The other guys I spoke to are still waiting to hear back from someone.

I was wanting to go with a Rheem Marathon MTS85345 or a CMTS85345 (apparently the canadian version is a bit different numbers wise). It's a 85 gallon tank with one backup heating element up high and two lower ports to circulate through the heat exchanger. They have lifetime warranties so long as I keep temps below 180F or so which is fine.

How often as a retailer do you get someone coming in saying give me X how much? Well they can't find it in the system. I instead got pricing on a MR75238 which is a 75 gallon regular dual element heater tank by the sounds of it. Looking online I can find specs but not a drawing so far... So this means drawing #6 for the inspector....

Anyways that's a horrible way to do business. Customers that know exactly what they want and have cash in pocket shouldn't have to be told we'll see if we can find one of those and figure it out. I also shouldn't have to be gouged by every person between me and the manufacturer. I spoke directly to 3 different heat exchanger manufacturers and all 3 passed me on to other people who couldn't give me a price without going back to the manufacturer. All 3 have now lost my business.

My current plan is to go with the 75 gallon marathon tank. Cost wise it's looking like my best choice out there for being the last hot water tank I'll ever have to buy. I'll have to figure out the plumbing to circulate out of the drain and back into the cold input or a port if it's available. For the heat exchangers Ebay and google both gave me dudadiesel this model in particular DudaDiesel.com Biodiesel Supplies

It's bigger then the dw4-6 in surface area so I'll need to redo the math. It's also 304 stainless not the 316 stainless I was hoping for. How much difference it will really make in the long run I don't know. looking around 304 is pretty damn common for lots of things and they just don't recommend using it with salt water. Anyways realistically the heat exchanger is more likely to fail due to clogging then rusting out.