# Going Solar heat, need opionions from people who do it



## Kevingr (Mar 10, 2006)

Here's my situation. I've got an old 2 story farm house that uses hot water baseboard heat, no in floor, all baseboard. 20 year old boiler. The entire house is getting a blower door test and completely reinsulated (dense pack cellulose). The insulating guys will be here 4 days and seal up all the leaks the best they can. Next phase is adding some solar panels.

I live in central MN about 70 miles north of the Twin Cities.

I've consulted with two "solar experts", one is a salesman and one is a consultant. They both have been in the business many years and they both have different ideas.

Solar consultant:
Replace the existing boiler with something more efficient in the 95% range. What he's recommending is basically a hot water heater with a propane heat element that cost's about 5 grand. He says to put up 4-5 4x10 solar panels, use the water heater as a preheater for the water heater and feed the baseboard with that. The water heater would circulate water at about 140F.

Solar Salesman
Replace existing boiler with a wall hung unit that costs around $1100. Put up a minimum of 5 4x10 panels, build a storage tank (similar to Solar Gary's, only put it in the basement). Attach PEX tubing between the joists on the mainfloor, and if possible on the second floor too (right now that'll work for half the upstairs). Use the lower temp water from the panels for the in floor heat and use the high efficiency boiler to make up the difference if needed, or in the rooms with no in-floor heat. In the summer use the heat generated by the panels to heat the pool (currently not heated), just as a place to use all the heat.

Salesman says Consultants plan won't work since baseboard heat needs about 180F water out and 140F back in to the boiler, the panel water could actually cool the water down making the boiler work more.

Both of these guys currently live off the grid in passive solar homes and supplement with wood. Salesman is in the process of putting up a 10kw generator on a 200' tower! Now that's enough to make a guy jealous!Salesman also has more day to day experience than the Consultant who has a real job too (in alternative energy related to bio-mass), consults on the side.

I'm leaning towards Salesmans solution. Anybody have any expericence with either solution and care to comment?


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## wy_white_wolf (Oct 14, 2004)

A little suprised neither of them said anything about evacuated tubes instead of panels. They can generate steam instead of water if wanted so getting 180 degree water for the base board isn't a problem. They are also the most freeze resistant since they don't contain water and what little is outside is usually ran as a glycol system instead of water.


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## Jim-mi (May 15, 2002)

In my area evac tubes are not a good idea because of snow.
Evac tubes are not good at 'melting' snow.
Even the soft brissle brush that I use to clear snow from my PV panels would scare me to touch those tubes.

Flat plate collectors here.

How large is your local snow fall . . ??


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## Kevingr (Mar 10, 2006)

Both of these guys recommended the same panel, from a local company here in Starbuck, MN, they both spoke very highly of them.

I think the "normal" snow fall amount in this area is in the 5 foot range, haven't seen that lately though.


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## WisJim (Jan 14, 2004)

My son used to work for a contractor building super energy efficient houses, and they used active solar hot water as heating in many of them. They did use in-floor radiant heat, so the temp required wasn't as high as for basedboards. 










That is a typical system--I think maybe near St Cloud, Minnesota. They typically had an LP boiler or hot water heater back up system, and some kind of wood heat also. The combination of passive solar designed into the house, active solar for most heating situations, and the excellent insulation meant that wood heat was seldom needed, and the LP backup was for peace of mind if they left the house for a week or more in the winter.

I like the salesman's ideas, but I think that there might not be enough details available to give a good answer. Maybe another consultation, but that might make things even more confusing.


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## SolarGary (Sep 8, 2005)

Hi Kevin,

I think that trying to use the existing baseboard with solar is probably a problem. The solar won't produce the kind of heat that baseboard heater like efficiently (including evacs). The baseboard heaters will produce some heat running at lower temps, so you might be able to use this in the more moderate months, especially with the new insulation.
You can run some actual numbers for both flats and evacs using this calculator:
http://www.builditsolar.com/References/Calculators/Collector/ColEfic.htm#efic

Hooking solar into a boiler system is tricky. I'm trying to do the same thing in my system by adding a boiler. As far as I can see, you can't "boost" solar storage tank temps up using a boiler. If you have a solar storage tank at (say) 110F, and the baseboard wants (say) 160F, then you would think that you can pull water out of the solar storage tank at 110F, use the boiler to boost it to 160F, and all is fine. But, that water will come back from the baseboard and into the solar storage tank at around 140F -- the net effect is that the boiler will be warming the solar storage tank. Not really what you want. 
A local HVAC guy who is adding solar to his system suggested a scheme in which the heat source is either solar OR the boiler. If the solar tank is hot enough to do the heating, than it is used as the sole heat source, and if not, it is valved out, and the boiler is used as the sole heat source. This seems to me like it should work, and its what I'm planning to do. It does not take a lot of plumbing or controls to do this. If anyone thinks this won't work, I'd like to hear about it.
You might ask them for a plumbing/controls diagram.

Even though its a lot of work, I think you might be happier with the PEX in the floor. 

A simpler alternative would be to use solar air collectors, or a sunspace that just dump warm air into the house during the day. For collector areas up to 8% or so of the floor area, the thermal mass of the house will store some of the heat to carry into the evening without daytime overheating. A slow ceiling fan or two can be used to even out the temperatures and distribute the heat. While this is not quite as technically satisfying as a system with tanks, pumps, heat exchangers, outdoor resets, ... its a whole lot less expensive and complicated 
Its probably what I would have done if I could have.

Please let us know what you decide to do. I'd love to see the diagram for the system.

Gary


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## Windy in Kansas (Jun 16, 2002)

Kevingr I'm appreciative that you are addressing conservation before the heating aspect. 

Though I don't like government involvement homes built in cities should probably be required to go through blower door testing with any issues addressed. 

I am not aware of blower door tests even being offered where I live. Would you mind sending me a PM or post with the cost of such? Thanks.


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## Kevingr (Mar 10, 2006)

SolarGary said:


> Hi Kevin,
> A local HVAC guy who is adding solar to his system suggested a scheme in which the heat source is either solar OR the boiler. If the solar tank is hot enough to do the heating, than it is used as the sole heat source, and if not, it is valved out, and the boiler is used as the sole heat source. This seems to me like it should work, and its what I'm planning to do. It does not take a lot of plumbing or controls to do this. If anyone thinks this won't work, I'd like to hear about it.
> You might ask them for a plumbing/controls diagram.
> Gary


Basically that's what the Salesman is proposing, but I'm not sure if his plan includes a valve to shut one or the other off. I'm still waiting to get the plumbing/controls diagram from him. I have no diagrams from the Consultant and not sure if he even plans on putting any together.

As far as air collectors I wish I could. I'm doing that with my shop since it has a nice big southern wall. I'm basically following what you did with your's Gary. The house unfortunetly was built on a north-south axis, so the bigger walls face east and west. I have very little exposure to the south. I also have the significant other factor where form rules over function .

The folks that are doing the blower door test and insulation are from the Mpls/St. Paul area and they do the Government low income insulation work around the cities. I decided to go with them because of the rigid requirements that the Government requires of these folks. I have to pay the full cost of the project, I don't qualify for the assitance from the Government. I'm hoping that I get a better job than the local insulating contractor who originally insulated this house during a remodel in 1986, and I'm not impressed with what they did. 

Windy, I don't know the cost of just the blower door test, but the entire insulating job is $5400. This months Home Power magazine in the Ask the Experts section someone asked about the cost of the blower door test and they said $200-$800. My house is about 1100 square feet per floor (2 story), they're doing all the walls and attic. I also have lower attic's (the house kind of looks like an old barn where the middle is high and has a lower section on each side of the high middle) that they will increase the R value to 50. They will seal up any opening from a lower level into an attic and they will close up open wall cavity's into the attic (ballon construction, 2x4's go two stories high all the way to the rafters in some places). They will also re-route 2 bathroom vents that currently go out the soffit and go straight up throw the roof, currently they leak terribly. In addition to the work they're doing I'm taking off all the trim on doors and windows and ceiling up with foam behind all the trim. I'm also replacing one exterior door and 4 windows. I'm also removing a chimney that is no longer used. I hope to have a pretty tight house once this is completed, but not too tight, the blower door test should let me know if I need any kind of air exchanger.

Originally I wasn't going to do all this insulation work, but I talked to a very wise and honest Outdoor Wood boiler salesman. I was thinking about going that route (decided not to because of all the work related to wood heat) and he said he can't sell me a unit. I looked at him funny and said why not. He said if I sell you one of these all you're going to be doing is heating the outside and you're going to complain about all the wood you burn. He told me to deal with the insulation first, then he'd be happy to sell me a unit. Now how's that for an honest salesman!


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## Kevingr (Mar 10, 2006)

Ok, here's the latest and greatest, I need a little help.

Consultant hasn't contacted me in 2 months so I assume he's not to interested in my project so I'm going to ignore him.

Sales guy gave me a bid of $24,000!!!!! That would be 5 4x10' solar panels, a storage tank (he doesn't specify size on his bid), all the piping and controls to put under floor heat, the ground mount (simlar to the picture above) and everything else to install an entire system that would only heat my first floor!!

Needless to say I've decided to go Solar Gary's route and do this myself. However, being so late in the year there's no way I can get all this in before winter sets in, so I want to get part of it done now and the rest in the spring. I won't be building a shed like Gary, but rather have panels attached to some kind of racking built on the ground. I'll build the panels over the winter and install them next spring.

I want to get the storage tank built (it'll be an indoor tank in the basement) with 5 copper coils for exchangers in the tank.
1) Input from the solar panels
2) Input from backup heat supply
2) Output to the in floor heat
3) Output to domestic hot water (future)
4) Output to the pool (summer dumping load)

So, here's my question. I currently use off peak electric for my domestic hot water at 
.045 cents/kwh. I need to add another tank because of more usage so I wanted to add a Solar Storage Tank with one heat exchanger coil and an electric backup element. Instead of the heat exchanger being used as "input" from solar panels to the tank, I want to use the exchanger as an "output" to my larger solar tank. Can I do that?


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## Kevingr (Mar 10, 2006)

I forgot to add in the results of the insulation project. The blower door test prior to the insulation was 2184cfm. The blower door test after all the insulation going in was 
868cfm.


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## SolarGary (Sep 8, 2005)

Hi Kevin,
Thats quite an improvement on the air infiltration.

I think that the big tank with many copper coil heat exchanger coils is workable. It gets a little expensive at the price of copper these days.

If the collectors could drain back to the tank, that would eliminate one copper coil, and would allow the collectors to operate a little more efficiently (no heat exchanger temperature drop). In this arrangement, the collector pump just takes water directly from the bottom of the big tank, circulates it through the collectors, and the water then returns to the air space just above the water. As long as the collectors are above the tank and the plumbing is all sloped, the water in the collectors drains back to the big tank when the pump shuts off -- this provides the freeze protection.

It sounds like you want to use the new hot water tank with the electric element in it to supply heat to the big tank for space heating via the heat exchanger coils in each and a circulation pump? 
While I've never heard of anyone doing that, I don't see why it would not work. You might want to think about what you would use for the controller on it.
In the summer, when there is excess sun for water heating, it seems like you could operate it in the opposite direction so that the big tank pre heats the water in the electric water heater tank.

I also wonder if you could achieve electric heating of the big tank by just putting a heating element directly in it that could be powered from off-peak power? This would eliminate two heat exchangers and a pump, but would not give you more hot water storage.

You might find this tank installation interesting:
http://www.builditsolar.com/Projects/SpaceHeating/AlanTank.htm
It has a nice simple tank design that just uses a hoop of sheet metal, and also uses two immersed stainless tanks to preheat domestic water in the big tank. 
I think that both this and the plywood framed tanks work fine.

There is an article in one of the last few Home Powers that has a big tank with copper coil heat exchangers for several heat sources and heat sinks -- similar to what you want to do. I'll see if I can find it, but you can probably search for it on the HP site.

Your heat dump loop might work fine with just a coil of PEX for the heat exchanger instead of copper. It really does not have to be too efficient?

Gary


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## Kevingr (Mar 10, 2006)

SolarGary said:


> Hi Kevin,
> It sounds like you want to use the new hot water tank with the electric element in it to supply heat to the big tank for space heating via the heat exchanger coils in each and a circulation pump?
> While I've never heard of anyone doing that, I don't see why it would not work. You might want to think about what you would use for the controller on it.
> In the summer, when there is excess sun for water heating, it seems like you could operate it in the opposite direction so that the big tank pre heats the water in the electric water heater tank.
> ...


I was leaning towards the closed loop because it gets so cold here in central MN. With temperatures in the -20F range not uncommon, is an open loop system really practical, do people do that? I'd love to go that route, much simpler. Putting the panels higher than the tank is already in the plan, sloping the pipe isn't an issue.

I need another hot water tank since my current one doesn't meet the demand currently, so buying a storage tank with an element in the tank solves two problems.
1) Gives me more domestic hot water capacity.
2) Provides a loop to the larger solar tank as a backup to the panels (if that works that direction).

That's a good idea about reversing the direction from the larger storage tank back to the hot water heater during the summer. The summer months are when I run out of hot water before the off peak meter turns on again, so that could solve that problem.

I've seen one tank, I believe it was Rheem, that had another hole for a temperature gauge, the problem is that it was on the bottom of the tank. I was thinking of using that hole with a regular solar controller between the Rheem tank and the larger solar storage tank. Water hot in Rheem tank, cooler in storage tank, turn the pump on. I'd need to put the pump on a circuit that is only on when the off peak meter is on though. Sounds like it might work.


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## SolarGary (Sep 8, 2005)

Hi,
My system is a drain back, and it has worked fine. We get down to -25F on occasion. The big thing is to make sure that the collectors and all the plumbing have a slope toward the tank.

There are a lot of drain back systems in cold climates.

The Home Power Article listed here in the "Hand On Basics" as "part 3: Drainback System" by Chuck Marken covers all the practicalities of doing a good drain back.

My system has some details:
http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm
If I had it to do over again, I might use the "U" tube arrangement to plumb the pump into the tank rather than penetrating the tank wall with the bulkhead fitting, but either way works.

With 5 collectors, the solar should provide very near 100% of your hot water needs in the summer as long as there is enough storage.
A lot of people with much less collector area just switch the electricity to the hot water tank off for the summer.

Gary


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