Solar water preheater project based on builditsolar $1000 system

[strider3700]

I've been planning and collecting materials for quite awhile now for a solar hotwater preheat system based on the BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution $1k systems.

In the past couple of weeks I got my data collection going at the house and have been working out how much my hotwater costs. The thread on that is here. http://ecorenovator.org/forum/applia...g-project.html over the last 15 days I've averaged 9.2 kwh per day just to heat water. Given my location I have a reasonable chance at achieving 70% solar heating. So with my current cost per kwh I can save roughly $198 per year with this system. possibly more because this savings should always keep me in the lower pricing tier and if I achieve 10% savings I get $75 from the electric company as part of a savings challenge... Estimating that the system should run about 25 years with any luck that works out to $11730 in savings assuming 6% price increases in electric and no change in usage. My kids growing up should account for considerably more even if the electric company doesn't get the 10% yearly increases they've asked for.

So with the math working out like that I finally decided to get going on the build and did up drawings with a buddy. Here is what we drew. My address is behind the grey blob....


I took that as well as a yard survey for my house which had a very rough drawing of the placement of the system in the yard to the city and asked for a permit. The basics of the drawing was the tank goes in my backyard, a line runs from the tank to a rear corner where the collectors are. I gave distances from the house and property lines since this will be a permanent structure. for the drawing it was a thin rectangle for the collectors a singe line for the pipes and a small box for the tank. Labels read collectors, inground supply/return lines, tank.

The city said they've never done one of these before but took the application to give to the plumbing inspector who wasn't in. I had to fill out a cover sheet stating the address it was going at, who would build it (me), who owned the property(me) who was applying for it (me)

Yesterday I got a phone call where they had a question. The wanted to know how high the structure for the collectors would be and what it was. I said it's just a wooden rack on the ground and it would be under 8' tall exact hight depended on the final angle of the collectors. They said that's fine but the plumber has questions still and I should call him tomorrow(today now).

Today I've tried twice to get a hold of him but it still hasn't happened.... He does go into the field to do inspections so I'm not shocked that he's not at his desk. So that's where that aspect stands.

So far materials wise I've collected the following

a dual pane sliding glass door with 2 34"x76" doors for free - I intend to split the panes and make 4 single pane collectors.
3x 12' 1/2" copper - $43.58
3x 12' 1/2" copper, 7x 3/4-3/4-1/2" copper T's - $65.45
9x 6' 1/2" copper $70.46
4x 8'x4' 2" polyiso for collectors $89.60
8x 8'x4' 3" polyiso for tank $268.80
40ish feet of 3" pvc pipe for trench $31.36
1 4x3x2.5 fiberglass hatchery fish fry tank. Roughly 150 gallon capacity - free
misc aluminum flashing, maybe 1'x15' worth - left over from other projects

bringing me to a total of $569.25 so far.

Off the top of my head still needed are the pump, a 500' roll of =3/4" pex, about 130' of 3/4" pipe insulation, some lumber for the collector frames, lumber for the collector rack, 3 shut offs, the tempering valve, the backflow preventor, a couple of 3/4" copper pipes. 3 more 1/2" copper pipes More T's and some more aluminum flashing. I'll be using my data logger as the differential controller. I just need to add a relay in place to control the 12V pump.

I buy when things are on sale or free... My hope is to get a final installed cost of under $1200 giving me a 5 year payback.

Right now I'm holding off on buying anything else until I get official permission to do it. After that comes in I'll start making collectors in my "free" time and I'll order the obviously necessary stuff like the pump and roll of pex.

[strider3700]

just heard from the permit guy. He's insisting on a double wall heat exchanger and recommends I contact solarbc.ca... that's the organization that pushes pro installs starting at way more then $1200 for systems that will do half as much. Next step is to contact them and find an inexpensive double wall heat exchanger. I'm not sure if I can do double wall and drain back and frankly adding the antifreeze to the system vs regular water is a lot worse in my mind anyways.

I'm not happy.

[redneck]

Inspectors can be a pain in the butt.

Sometimes it's better to seek forgiveness than to ask for permission...

>

[Daox]

Did you ask why you need a double wall heat exchanger when you are just using water?

[strider3700]

Yep and the answer was because the new code says double wall only. Basically the inspectors way of saying I'm not thinking about this.

I think I may have a solution that may be close in costs.
The old exchanger was 300' of 3/4" pex would be about $200

here's my new thought off the top of my head and 10 minutes of research



basically an approved double wall flat plate exchanger a second pump and some form of flow sensor telling me when to activate that pump (only when hotwater is demanded basically).

pumps are $65, ebay suggests a 40 plate exchanger is $120 but I need to do the math to see if it's large enough. flow sensors I've yet to research but I can't imagine they are too much. The bucket is a bucket and a leak detector should be cheap cheap available off the shelf anywhere.

This only works because I have an arduino for my temperature controller and a change like this is 1 extra relay and some code.

I need to do the math on the flat plate exchangers to figure out exactly how many sqft of surface area I need...

My wife's response was not fit for public ears and she said just do it.

[RobertSmalls]

If you've decided to rule out the Redneck approach, I'd get a copy of the official requirements in writing. Has your town actually passed legislation requiring solar hot water collectors to have double-wall heat exchangers, or have they adopted standards set forth by a society of engineers? If the latter, I'd write to the folks who maintain the standard for guidance.

[strider3700]

At this point I'm trying to play nice. I'll try to track down the code requirements but if it's not a huge change in cost It's not worth the fight. 1 plumbing inspector in town...

[strider3700]

Does anyone have any experience with the flat plate connectors? I'm trying to figure out if I can get away with my drawing and only have 1 pass through the xchanger before going into the electric tank? most installs would circulate the hotwater tank through the exchanger using 2 pumps. They also tend to have 1 pump sending to the panels and no storage tank so the entire system is just 2 pumps. With a storage tank I'd be at 3...

The goal is for a gain from 50 to over 110F passing through the exchanger at the same speed as the water is coming into the tank so 2-4 gallons per minute would be my guess. The hot fluid would be hopefully 130-140F and flowing at whatever pump rate I need...

[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).

[strider3700]

So after doing all of my research and finding a bunch of examples of single wall systems listed as for sale in BC and meeting the CAN/CSA - F379 requirement which the BC building code says they have to meet, I went downtown with printouts from those manufacturers as well as a printout from SolarBC which listed various systems in a table and showed if they met F379 requirements or where still under testing and if they where single wall or double wall heat exchangers.

I met with the city inspector and showed him a new drawing I had done where I was going to use a commercial DHW storage tank with internal heat exchanger that met F379 requirements and just pump the solar fluid from my 160 gallon tank through that coil giving me a really big hot solar fluid tank and a preheat tank before my electric hotwater tank... I then pointed out that these commercially manufactured and approved tanks are single wall heat exchangers so how is this any different then my original proposed system? I then provided the printouts from the manufacturers websites describing the systems.

I then asked if I could see F379 since it is what I have to meet and I can't get it for free. He told me he doesn't have a copy because it isn't out yet. This is where I think things have gone off the track. To make a long story short he heard at a conference that they are going to change the requirement to be double walled and there was some sort of uproar about that but that is where he got the basis to reject my system from. I pointed out that the 2006 BC building code has 2 entries on solar and they both say it must meet the national code which is F379 and F383 which means in 2006 both F379 and F383 must have existed. As well I saw that a new version of F379 at least came out in 2008 and a new version was in the works but was not released yet so nor had I seen a date on when it would become the requirement. I mentioned that the US code has a single wall specification that made it ok under certain very safe circumstances and perhaps something similar was in the Canadian code. He rightfully didn't overly care much what the US code says.


He mentioned hearing that installations in Burnaby had been ripped out due to having single wall heat exchangers. I can't see how that wouldn't have been grandfathered like pretty much everything else is. Perhaps it was a commercial install and insurance wouldn't cover it but the city shouldn't be able to make you change what they already approved.

So basically the inspector had not done any research and had just said no based on something he overheard at a conference. In the end he took all of my printouts and said he'd do some research but it would take awhile. Hopefully he has better luck getting answers back about this from someone then I have. My next step is to start talking to some of the solar suppliers about their single wall units and see how they are OK in BC. They must have read F379. So far SolarBC the advocacy group for solar in my province hasn't even responded to my emails.