Solar Hot Water (Part 2)

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The lessons that I learned from the computer model of our solar hot water system are as follows:

  • insulate the pipes leading from the basement to the collectors to at least R6, preferably R10
  • insulate the storage tank to R50
  • install a 1000 litre storage tank
  • install 3 collectors
  • there is extra heat - install a system to harvest it

We bought the collectors, drainback tank, pipe insulation and other knickknacks from Trimline Design Centre just down the road from the Mill Creek NetZero Home. My builder Peter was very impressed with the clever, simple design of the flat plat collectors that Trimline manufactures. Yes, that’s right, they manufacture solar hot water collectors right here in Edmonton!

Overview

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(schematic of the MCNZH solar hot water system)

The three collectors will heat water in an R50-insulated 1500 litre tank that I'll call the "pre-heat" tank (the schematic incorrectly indicates that the pre-heat tank is only 1000 L). The municipal water will first pass through a drain water heat recovery coil, and then enter a 200 foot coil of copper tubing that will be inside the hot water tank. The water in the pre-heat tank (the 1500 litre one) will be for storing heat only – it won’t be potable. Anyway, the water from the city will first go through the 200 feet of copper tubing before it reaches the 50 gallon electric hot water tank, the "top up" tank.

We are also adding a means by which to use extra solar heat for space heating, but I’ll talk about that in another post.

Collectors

We installed the collectors on the roof, put a drainback tank in the loft (the water drains back to the tank when the sun isn’t shining, preventing it from freezing), and ran copper piping to the basement mechanical room.

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(a solar hot water collector in the living room – at 8’x4’, they’re bigger than they look from the ground!)

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(Tristan soldering fittings onto a collector)

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(installing a solar hot water collector. I’m the guy being useful – that’s right, hands in the pockets)

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(Peter Amerongen, president, Habitat Studio & Workshop)

Pipe Insulation

My modelling informed me that lack of pipe insulation might be the single biggest mistake that people make when they build these systems – in the MCNZH the pipes run up over 8 metres, so their surface area is significant. We insulated them with Armaflex’s Armacell pipe insulation. It’s a closed cell foam insulation that can withstand the high temperatures of a solar hot water system.

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(Armaflex pipe insulation)

We got a bunch of 1” thick stuff, and also some 3/4” thick insulation because they didn’t have enough of the thicker stuff. That brought the insulation value to somewhere between R3-R5.

We then supplemented that with foil-backed insulation:

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(the pipes that run hot water from the basement tank to the collectors – we couldn’t fit any more insulation in the wall cavity)

That gets the insulation value of the pipes up to a ballpark of R6-R10, right where we want it.

Tanks

Originally we had planned to use a tankless hot water heater to top up the heat of the water, but we decided against it to reduce complexity and cost. Some tankless hot water heaters don’t work well if the water coming in is preheated, you need to have special electrical wiring to handle the surges, and the tankless models cost 2-3 times more than a regular hot water tank.

Standard electric hot water tanks come off the shelf quite poorly insulated – R10 or so I believe. We’ll add R40 insulation to the top up tank so that our standby losses are reduced to 10-15 Watts. By doing this we'll be making an ordinary $300 to $400 electric water tank almost as efficient as a demand heater that would cost considerably more to buy and to install.  Our annual standy losses will only be about 40 to 50 kWh per year if you consider that in the middle of summer the standby losses will be mostly be replaced with solar (that water in the top up tank will be so hot that the losses won't matter) and in the heating season they will heat the house.

We built the pre-heat tank ourselves, and had a hitch or two before we achieved success:

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(Tristan lining the 1500 litre hot water tank for water tightness)

We built a box with 1500 litres of volume, then decided to line it with a roofing material for flat roofs:

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In retrospect, we were doomed from the beginning – water will find a way through an seam no matter what. We filled the tank partway with water to test it:

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and we soon found a tiny trickle of water leaking out. The next step was to line it with a pond liner that landscapers use:

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Without seams, this solution seems to be working for us. We’ve had it filled with water for about a week now. The seamless membrane is 45 mil EPDM material that is sold by Canar Rock Products as a pond liner.

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The top up hot water tank will be placed beside the bigger tank (where the ladder is in the picture above) and surrounded by insulation.

One of the last components that we needed to build was the heat transfer coil. Cold water from the city will pass through 200 feet of this before reaching the top up tank.Tristan built a frame out of PVC pipe, and created the coil by wrapping soft copper pipe like so:

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So we have the collectors, insulated pipes to the basement, an insulated heat storage tank, and a coil to transfer the heat to the potable water. We’re almost ready to hook everything up and see how it runs.

(cross posted at raisingspaces.com)

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Hey Conrad, I've got a couple of questions for you: Firstly, where did you find the Armaflex insulation? Secondly, do you know what you will be using to cover the insulated pipes that are exposed outside the roof? Again, I'm looking for where I can purchase the supplies I need for my installation.

Ken

We bought the Armaflex insulation from Trimline.

I see that Armaflex now has a UV-resistant product, but we're going to build a cover out of PVC pipe.

Conrad

The collectors look identical to Thermo-Dynamics G32 panels (made in Dartmouth, NS)
http://www.thermo-dynamics.com/technical_specs/G_series_technical.html

-Ralph

3 collectors is overkill. I have a single G32 panel for my family of 6, living in Nova Scotia. At ~$800/panel and 1.8c/1000BTU for backup water heating the 2nd panel didn't make economic sense.

The German PassivHaus standard targets 25L/person/day of hot water. I'm pretty close to that (<30L/person/day) and expect to beat it after I adjust my plumbing to get more precise measurements of actual hot water use.

Maybe all that biking around means you need to take more showers? ;-)

-Ralph

Ralph,

I've never seen a system with only one collector. An argument could be made that 3 is too many, but I'm confident that 1 is too few. Have you measured the system's solar output? I can't see you getting more than 50% of your hot water from solar.

Obviously we have different values when it comes to spending money on this kind of stuff. My goal is to push to the limit, not just pick the low-hanging fruit. Getting to net zero energy does not "make economic sense" if you subscribe to today's theories of economics (the ones that take infinite growth for granted).

It's funny that you mention the biking, because the $800 that you saved on that extra panel, I save every two or three months by not owning a car (versus a family with two cars). I'm spending some of that disposable income on this house. My "return on investment" is the feeling of "doing the right thing" and protecting against the downside risks of the problems that our society risks moving forward. People who spend their money on cars get different returns for their money. Most of the time, those returns don't involve an increase in financial security or feeling good about making a positive step for the environment.

Conrad

Conrad,

My collector provides more than 50% of my hot water because my family uses less hot water than average. If going without a car is "doing the right thing" then wouldn't going with 2 collectors while using 33% less hot water be "doing the right thing" as well? In fact you could get 100% of your hot water from 2 collectors while decreasing your usage by less than 33% by adjusting your usage patterns based on the supply of hot water; i.e. don't use backup heat.

I like beer, but at over $1.50 for a bottle, it doesn't make economic sense compared to drinking the apple juice I bought for 65c/1.2L can). I still have a beer now-and-then, but I don't try to evangelize my choice.

I find much of the information you've provided quite useful. A lot of it is solid science, and some is your values. I'm interested in the science, but not the values, as they are not rational.

As an example of why they are not rational, it would be better for the environment if everyone in a very cold climate (i.e. edmonton) moved to a moderate climate (i.e. coastal Mexico) instead of spending large amounts of money on trying to have a net zero home.

-Ralph

Ralph,

I am giving the reasons for the choices that I have made. Those reasons are based on my values, and so I must discuss my values when explaining my reasons. That's not evangelizing, that is defending a position. I didn't knock on your door and try to convert you, you started commenting on my website.

No one has perfectly rational values. Decrying my values as non-rational, and thereby implying that yours are, is behaving in a non-rational manner.

Your first argument is a straw dog because we will be using a bare minimum of hot water - in a previous post I estimated 30 litres per person per day (one of them will be a renter that we will have no control over). My modeling with WATSUN, which I believe is too optimistic, estimates that we'll be getting 90%+ of our hot water from solar as well as 1000kWh per year of space heating. That is much more than a system with one collector would get, and the extra money to get that energy is worth it TO ME, because of my value system.

Conrad

Hi Conrad

Good work!

I agree with what you are doing regarding "overkill". I have said this before and I don't think Ralph understands it. You are planning for a future with high energy prices, where all these investments made today will pay-off big time. I think many people in general don't think this will happen as we are such a resource rich country and we have a government that provides a lot of services to the people like health insurance and such. They expect the government to take care of them and keep energy prices stable. The problem is the energy may not be available.

I have 30 tubes on my roof which may be equal to 1 1/2 flat plate collectors. I am not sure of the output, it is a Viessman system. I wish I had more. I would have gone with 40 if I could do it again. It is only for DHW.

Here's how you can handle people like Ralph. I have another renewable energy project I am doing. It is running my work truck on waste vegetable oil. What I do is I call it a "hobby". I don't expect to save money even thought I get the fuel for free. After I consider all the money I have spent on filtering equipement, truck parts, and especially my time spent collecting the oil, break even is a long way off. So I call it a "hobby". I do it because I enjoy it. I like working on my truck (ok, not always!) It makes me feel good knowing it is good for the enviroment. I am showing a good example for my kids. I have been doing it for several years and I still get a kick when people smell the exhaust and think someone is having a bbq. (the exhaust smells like fast food) The biggest kick was driving by the pump last summer when diesel was $1.47L. Now if prices had stayed at $1.47 or had risen, that break even point would be a lot sooner.

Good for you Conrad!

Conrad,

You conveniently ignored the part where I said it isn't rational for me to spend money on beer. Both our values are irrational. That's why I want to focus on the science. You can help people be more energy efficient by focusing on the science. It seems you like people telling you your values are good...

Ralph,

Sorry, I didn't catch that the first time around. I retract the "rational" comment.

I personally am interested in examining values. Your were willing to put in a solar hot water system - that's more than what most people are willing. So why do you draw the line where you do? What rate of return do you demand before you're willing to spend the money?

I also think that you should qualify that rate of return before declaring a given investment overkill.

Finally, I didn't mean a personal attack when I mentioned cars. I just find it ironic that many people (not saying you) will spend many thousands of dollars on some things without a thought - driving is an easy target because it sucks up so much of our disposable income - but focus almost exclusively on rate of payback when evaluating renewable/efficiency investments.

Conrad

Conrad,

Thanks for the apology. I don't want to attack your values; I want to learn how to be more efficient as an individual and a society.

I bought 2 Thermo-Dynamics G32 collectors at a cost of almost $800ea. One I installed on my house and the other I am installing on my parents. If one collector saves $300/yr in electricity, installing 2 collectors will save much less than $600. However installing 1 on my house and 1 on my parents will save more money than installing 2 on my house and none on my parents.

Although your budget for energy efficiency is larger than most, it is still finite. It is possible (and I assert likely) that investing the $800 somewhere else in your house would save more money (vs buying the 3rd solar collector). Maybe you could have upgraded your north-facing windows to PassivHaus standards. Or maybe buying a drainwater heat exchanger would have a greater payback. http://www.watercycles.ca/products.php By quantifying the ROI individuals and society can more efficiently allocate our finite resources than if we make decisions based on feelings or values. The value we do share is an interest in energy efficiency. The reason I participate in forums like this one is to learn energy efficiency techniques that are quantifiably beneficial, and to share data on what I've learned about energy efficiency.

Regarding the car thing, I agree that it is not necessary for most single people to have a car. Before I got married and had children I lived in Ottawa and had no problems making due with a motorcycle and public transit. You will make a much larger impact educating parents on economical and efficient vehicle choices instead of trying to get them to forgo vehicles. If you ever have the fortune (I use that word but there is no word in English for what I'm trying to say) to have children, you will likely want a vehicle if for no other reason than emergencies. I know of no parent who, given the choice, would wait for the bus or drive their bicycle to a hospital 15km away when their child needs prompt medical attention.

-Ralph

This is getting off topic, but I want to address the cars and kids thing. Conrad has two kids and lives about 5-7 minutes (by ambulance) from the main children's hospital as do I. There are at least 4 other car free families I know of with up to 3 kids who live in this neighbourhood (quite likely more). I have 5 kids and a vehicle. But not to get them to emergency -- that's the ambulance's job -- with 5 kids to pack up even a vehicle isn't going to get me there quickly enough if quick is what is needed.

I can't bike with five very easily by myself yet. Two are on training wheels, two in a trailer. Takes about 30 minutes to go about 8 blocks and that doesn't count getting ready to leave the house. We're doing it sometimes, but it's not efficient. Eventually the two on training wheels will be strong bikers, but then I'll have two more on training wheels. Someday, we may be car free but I expect that's a good 7 years away -- that being said our family of 7 has only put about 20000km on our mini van (the most energy efficient in it's class, but that's not saying much) in the last 3 years and probably half of that is road trips. We just don't drive much. Some grocery shopping, errands, some activities. My husband buses or bikes to work.

Depending on where you live, it's quite possible to have kids and be car free.

Kirsten,

I agree it is not only possible, but even practical in many cases to have kids and be car free.

Trying to convince parents to be practical about how they care for and protect their children is, I think, a waste of time. Getting parents/homeowners to be practical about how they maintain and use their home & vehicle (i.e. be more efficient) is something I see as more likely to bear fruit.

-Ralph

Conrad, thank you for sharing so much great information about your new house. It's very inspiring to see what you have accomplished. By the way, my 33 year old house in Edmonton leaks air at 6.98 ACH @50 Pa. I'm working hard and spending $$$ to fix this but it's hard to address all the problems. It's seems that many builders and renovators will cut corners when it comes to sealing and insulating if the consumer can't see it.

A few questions: In your schematic of the MCNZH solar hot water system above, you show a "mixing valve" downstream from the "top up" electric water heater so it looks like you'll mix hot water with domestic cold water to create the actual domestic hot water distributed to your house.

What is the purpose of this valve?

Also what is the expected energy consumption (kWh) of your solar water pump?

-David W, Edmonton AB

David W,

The mixing valve kicks in if the water coming out of the tank is too hot. It is to avoid scalding.

The pump will consume ~150 Watts.

Conrad

Thanks Conrad, I've been researching Solar Heating systems and see that many systems on the market use an anti-freeze solution to transfer the Heat between the collectors and the Hot Water tank. Can you discuss why you chose to use water as your heat transfer medium?

David

Want to go solar over my front deck 6' by approx 21'. It faces north west. is it worth the time to think about this. I see you have tilt on you awning and I was wondering if it would go past 90% so i could pick up the south sunshine. If set right any water would drain to the eavestrough on the front of house.

David,

We were going to use only water because it's a drainback system. In theory then, the water should all drain back whenever there isn't enough sun to heat the water properly. We chickened out in the end, though, and we are soon going to add a percentage of glycol to the heat transfer water just in case of controller failure.

Conrad

you said mill creek net zero home? i live right by milburne mall. i would be interested in seeing/talking about this system. i dont have a lot of money to do this stuff and my house doesn t seem to be placed right for it (most winter sun is blocked by trees and condos), but i still find the whole solar thing interesting, and wonder why more of it isn t around.

by the way, in my travels on the net looking for solar heating, i stumbled on stirling engines, which can be run solar, but im not sure how big of an operation it is for a home. then i stumbled on micro chp systems that have been used in japan for years and are just emerging in the european market (too bad its 220 volt).these are usually run on natural gas heated stirling engines which use heat to run the engine which turns a generator, and the excess heat is used for heat and water. (but we know these things will run on solar). sorry just thought i would throw that in. if anyones interested, heres the wiki links.

http://en.wikipedia.org/wiki/Stirling_engine
http://en.wikipedia.org/wiki/Micro_combined_heat_and_power

Hi. Wonderful project.Would you mind telling me exactly what type of copper you used for your heat exchanger, and why you went with that grade? K,L or M. We want to install a heat exchanger in a solar hot water cistern and am not an expert on copper pros and cons. Thanks!

Hi,

We used air conditioning tubing because it's cheaper. It's thinner wall so less copper is used in its manufacture. It is 3/4" Outer Diameter (OD).

Conrad

Hello Conrad

Thanks for a great website.

You state above that you intend to talk about how to use the extra solar heat for space heating.
I can't seem to find any additional information on your website.
Did you ever get around to explain this?

Did you ever consider replacing part of your windows with a passive solar collectors like
these:http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm#Passive

This will reduce the heat loss at night as the passive solar collector can be disconnected at night.
The passive solar collector should also be quite a bit cheaper than a window.

The downside is that you won't have quite as good a view of your garden.

Conrad:

I just became aware of your website and will peruse it further as time goes on. I live in Kelowna b.c. and installed a solar domestic hot water system several years ago. It is two panels (one 16 tube sunda) and one 24 sq. ft. flat panel. It works well for us as we have reduced hot water use. Winter isn't very good here due to mostly overcast weather but we still get some supplement to our hot water use.

I am wondering where you located/bought the foil wrapped insulation used over the armaflex pipe insulation? I would like to add something like that to the armaflex I have currently installed on my pipe.

Thanks again,

John.

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