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Old 11-30-14, 03:33 PM   #11
sunspot
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Originally Posted by randen View Post
Sunspot
Your investing a lot of time and energy to a new system. I would humbly suggest to educate yourself in the low temperature heating methods.
Randen, thanks again for the detailed replies.I know how much effort it takes and am very appreciative of the time yourself and others put in helping the rest of us.

I've read a bit about low temperature heating here and elsewhere but I'll read more and see what I can pick up. I agree with in-floor heat option where possible. I did an installation in a bathroom for my sister years ago and that small space became everyone's favourite place.

The cutting, splitting, stacking of firewood is a big job but so far I enjoy it. And we don't burn that much (< 3 cords/year)considering it's our only heat right now. It's a rare morning the stove gets lit at all - weekends. Usually I start the fire around 4 pm. The house heats quickly upstairs where the stove is located. The bedroom, bathroom, and guest rooms are downstairs and are cold. These are the rooms I want to distribute heat to and, unfortunately, they have finished floors on sleepers over uninsulated slab on grade. Our bedroom is only a few degrees above ambient. I measured it at 4 degrees C a couple of weeks ago. The mattress heater makes this tolerable, comfortable even.

I should explain that I'd consider solar space heat a bonus as the weather on Vancouver Island in the winter is a lot of overcast and rain and not much sun. When the sun does shine the south facing windows let enough sun in to heat the house dramatically. This is part of the reason I'm considering the less than optimal winter angle of roof mounted collectors. Significant winter gain might be a pipe dream at best. If all we can hope for is lots of hot water in the summer we'll be content with preheated DHW (I did put pipe in the wall in case we end up with enough to dump some to a small hot tub just in case).

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Old 11-30-14, 03:35 PM   #12
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randen,

Sunspot didn't say what part of BC he's from...

I just took a guess as to his location (guaranteed to be wrong) that his location is Victoria,
-AC
Close! I'm about 250 km north of Victoria.
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Old 11-30-14, 05:33 PM   #13
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I assume you will use copper to go from the panels to the tank. PEX won't last too long with the kind of temps you may experience. I've seen lots of burst DIY systems with PEX. It will be less of an issue if the panels are at 80-90deg but at the normal pitch of 45-60 deg, I would be concerned.
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Old 11-30-14, 11:49 PM   #14
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I assume you will use copper to go from the panels to the tank. PEX won't last too long with the kind of temps you may experience. I've seen lots of burst DIY systems with PEX. It will be less of an issue if the panels are at 80-90deg but at the normal pitch of 45-60 deg, I would be concerned.
That I didn't know. Disappointing. What's a 'safe' temperature for PEX? I'll want to limit the temperature regardless of collector angle for peace of mind.

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Old 12-01-14, 06:19 AM   #15
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It really depends on a couple of things whether you need copper all the way. The first is the angle, as we discussed, and the second is the specs of the panel, the absorption and emission characteristics of the panel.

On this I have a big bone to pick with the SRCC way of representing the performance of a panel. The rest of the world states absorption as No 0.750 (for example) and is an absolute value. Then it states the major collector losses as W/(m2K) such as 4.50 W/(m2K). The lower the losses the better. But SRCC (aside from changing it to btu), presents the numbers as BTU delivered on a cloudy day, sunny day etc. I feel that this is all people look at and they don't learn what the other terms mean. It dumbs down the process.

Anyway, back to your issue. A DIY collector will typically not have the good loss number (poor- 6W, good 3.5W, for example) and the higher the loss numbers, the lower the stagnation temperature, or the lower the maximum collector temp will be with no fluid flow at 1000w/m2 of sun shine.

A really good flat panel will sit there in these conditions at over 200C and a lesser efficient one will sit at 150C. Even 150C is too hot for PEX as it is rated for 80C temps (although this is only the CSA test procedure, they can go much higher. Especially PEXa tubes such as REHAU and UPONOR), but 150C is not good.

At the very least there needs to be copper for the first 2-3M from the panel with a DIY panel, but copper all the way is a way better bet.

This is not to say that a manufactured panels with a higher losses number is bad panel. Remember that the vast majority of the time we need collectors temps of 50-80C and not 150C (a pump won't run at this temp anyway, the control won't let it). This is why I would rather see an extra panel or two than pay to have a higher efficiency panel.

Last edited by Mikesolar; 12-01-14 at 06:25 AM..
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Old 12-01-14, 08:57 AM   #16
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I'm breathing a huge sigh of relief this morning. ~5 m of copper is easy for me to do. All the way back to the tank, much more difficult.

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...the higher the loss numbers, the lower the stagnation temperature, or the lower the maximum collector temp will be with no fluid flow at 1000w/m2 of sun shine.
I'd like to understand the above better though. Would it apply to a drain back system? I'd have thought no fluid flow would equal no fluid in the collector. A call for heat would then flood the collector with relatively cooler water and the collector temp would instantly drop before any water made it out the return line.

There's so much to know, it keeps it interesting. I hope other DIY'ers stumble on this information early enough in their process to make a difference. It's like driving though. A person doesn't really learn until they've already got the license and are in the thick of it.

Thanks Mikesolar.
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Old 12-01-14, 03:51 PM   #17
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While it is true that a drainback system is "less" prone to transferring the "over heated" heat to the tank or tubing due to the lower thermal mass (the thermal mass would then just be the tubes, fins, headers and not the 1.5L of liquid, per panel, which would be there in a glycol system), the first bit of water that exits the collector could be superheated steam, then very hot water. Depending on the flow rate of the pump, the very hot temps could continue for some time. But, many drainback systems need high head pumps that also are at a higher flow rate than a glycol system so the temps will be a bit lower.

BTW, don't put an auto air vent at the top of the system. If you are having a closed loop system with a big coil in the tank, you can use an iron body pump in the system (cheaper than bronze) and the O2 in the loop will never be replenished to rot out the pump. However, if you are pumping and dumping into the big tank, the bronze pump is needed.
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Old 12-01-14, 05:43 PM   #18
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Default You wish to heat with solar Eh??

Mike & AC Hacker

Have both brought up some interesting thoughts. AC Hacker mentioned about the solar insolation of your area of the planet. My thoughts didn't encompass the amount of solar energy that was avalible to you. HMMM

Here in southwestern Ontario I'm a little disappointed at times with the amount of sun I receive some seasons. When I was going though the thought processes I was marking a calendar for the days of winter we received full sun. That season I marked more than half with a usable amount. I found this attractive. Also: (1st) I already had in-floor heat. (2nd) Solar PV was still quite costly and Solar Hot water I could fabricate myself. Other details was I have an abundance of south facing wall unencumbered. and we were in need of replacing faulty windows and stucco finish that was installed improperly. It was an episode right out of Mike Holmes on Homes. We went forward with the project.

I must caution you that the amount of sunlight you receive there in Victoria may leave you disappointed.

I will leave with some further food for thought. What about Solar PV augmenting some heat-pumps with electrical energy. PV panels will still make some watts in obscure sunlight that can help power some heat pumps. Were as Solar hot water will fall on its face. Your climate would work well with air to air units. Heat pumps or spilt units can provide as much as 3.5 times the amount of heat energy for 1 unit of electrical energy.

Solar PV are a bargin now and I believe B.C. has some nice incentives that could work in your favor as well.


Or better Hack a couple of HP for air to water for the big water storage tank. During the day the HP can purr away warming that water storage tank with some watts offered up from the PV. After the sun is set and you've made it in the door and settling in for the hockey game. It would be totally up to you to light a fire or not. The heat-pump may have heated the tank to 50 Deg C that could keep the whole home warm through the night. Or a fire to heat the tank further to 60-70 Deg C so the HP wouldn't even run the next day.

I think its so cool that our technology of today can have us thinking like this. Twenty to thirty years ago it was either gas oil or electric resistance heat.

Opps almost forgot about my friend Mikesolar. If you go the route of solar hot water use the best materials you can. This DIY stuff can last for decades dropping huge amounts of BTUs into your tank. The last thing you want is plastic getting soft and fittings slipping out. Copper will go the distance. Drain-back, you will offset the cost of a bronze pump without needing the cost of antifreeze and a heat exchanger. In fact pure water can carry more heat than a mixture of antifreeze and water.

Your going to save money by doing everything DIY use that money on good materials don't be frugal here!!

Randen
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Old 12-01-14, 08:50 PM   #19
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Thanks for clarifying Mikesolar. I'll swap the inlet and outlet ends of the collector(s) from what I was planning to make the return longer providing additional copper buffering pipe before connecting to PEX.

And I'll look for a bronze pump. I don't mind spending the extra where it's warranted.

randen, "What about Solar PV augmenting some heat-pumps with electrical energy... Or better Hack a couple of HP for air to water for the big water storage tank"

Waaaaay too high tech for this hillbilly. I've no doubt those options are better in every way but the woodstove speaks to my level of sophistication. And if it takes electrical energy to operate it will be a hard sell here. We've made a bit of a game of reducing our electrical consumption to the point our bills average $35/month year round. No dishwasher, no clothes dryer, and we cook on the woodstove for half the year. I do leave 8 4' flourescents running 24/7 in the winter months to keep condesation off the machinery in my shop but otherwise we're frugal. And it's not about the money really. More the challenge and an ethic I certainly don't need to preach to you.

Funny thing, when I look at the "big water storage tank" my thoughts often drift to the two 3363 US gallon (6726 total) water storage tanks fed by a rainwater collection system we use in lieu of a well and what could be done with that thermal battery! If I live long enough maybe I'll dig up the lids, get some insulation,... ... ...

But before I did that I'd look long and hard at a PV install like pinballlooking has done and generate income from the grid for a change. Now that's something I could get interested in ;-)
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Old 12-01-14, 10:23 PM   #20
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Default Solar hot water EH?? Maybe PV

Sunspot

Ok we have you thinking now. Don't get us wrong we all speak hillbilly. Nothing wrong with burning wood.!!! Even burning wood in the masonary heater brings this carbon neutral method of staying warm into the new millinium

But as we age, the chainsaw and splitting maule gets a little heavier. As we repeat the behaviour every year, the mind may ring with" I should be working smarter and not harder."

The price of solar PV had prevented me from moving forward with that as opposed to the choice of solar hot water. It was a financial decision of return of investment. (ROI) But today the price being less than $1.00/watt, Bring it on.!!

But you have some other circumstances that whey in. The climate of Victoria makes an split heat-pump (air to air) viable. These HPs are very reasonably priced. (keep in mind the efficiency 3 units heat for 1 Electrical energy)
A solar PV panel will produce a few watts of power (that can be used) in a condition of overcast but a solar hot water will produce nothing usable (ask me how I know)

Now another facet to consider is like pinball to sell the green electrons to the grid at a premium price and buy it back at a reduced rate. Eyeballing the ROI.

It maybe a little heavy to think about, so for your homework check this out, this should make you question a lot of the common practices.

DIY Geothermal Heat Pump + PV System - No Heat Bills!

I totally applaud your reduction on the electrical front. Amazing. $35.00/ month. So this PV powered HP maybe right up your alley.

As you are more than aware all these technologies work and work well. From super insulations and draft sealing to solar hot water, PV, Heat-pumps and the roaring wood fire. We are all looking for the best bang for the buck. It's a human condition.

Randen

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