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Ideas: Solar PV, Radiant Thermal for Major Renovation

Sun Feb 02, 2014 9:51 am

Hi, working on plans and permits for a major home renovation in West Los Angeles. Look to use smart energy management and electronic management for heating, passive cooling, lighting, access control, etc.

This LEAF community seems to have extensive knowledge and interest in efficient home energy usage and production, along with electronics and networking, so reaching out for thoughts and more informed thinking seems to be a good idea.

In WLA, there is great sun most of the time in this area (minimal marine layer clouds); the house has an unhindered south facing roof. I am looking for engineering ideas that will make best use of existing technology.

The home construction is a typical stucco house, with a perimeter foundation and crawlspace. Will be catching low hanging fruit of using insulation and natural light when possible, and all windows will be updated to double pane, etc.

A standing seam metal roof rather than composite shingles is specified to replace the wood shingles (making budget would be the factor to go to asphalt shingles). I've seen clean elegant looking clip systems for Solar PV mounts that maintains the roof integrity with standing seam, and I like that.

Added to floor joists and ceiling and or attic, updated windows, doors. Amazingly, there is currently none.

I like radiant heat, especially on bath and bedroom floors, and am likely going to use to distribute the solar thermal with a boiler supplement. It is very rare that mechanical cooling would be required--planning on using whole house fan to cool at night and thermal mass to keep cool during day (works pretty well this way now even without any insulation). I've also seen venting systems with smart thermal sensors that take advantage of micro climates of the house, pulling warm or cool air inside to augment the passive and radiant features, but have never seen an actual install.

The use of micro inverters appeals to me because of the redundancy, elegant failure, but I'd be open to a persuasive argument for a straight DC system with a main inverter.

The site has a pool and spa. This could possibly make use of a heat pump, and/or heat dump for excess solar thermal production in the Summer? Also, heating a pool with natural gas just seems dumb. However, one solar PV engineer feels that mixing the energy from the solar hot water energy (even in a closed system) from the house supply is a bad idea. Specific thoughts on this?

Simply not considered, but again, the pool and spa (both will have covers and have a planned surround of insulation) present a large thermal mass to be managed and perhaps utilized. Seems too complex and expensive but I've heard if the pool is used it might qualify for the 30% Energy tax deduction.

Held for added topics and inclusion of comments....

Perhaps you've slogged through this post and are willing to help. I'd like to be able to showcase state of the art engineering and technology... Looking for vendors and manufacturers to consider, and whatever may be of help for the good of the show....

Thanks, Jim

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Re: Ideas: Solar PV, Radiant Thermal for Major Renovation

Sun Feb 02, 2014 10:28 am

Cool! I'll be very interested in your progress.
Do you have a metric for what sort of energy efficiency gains you're looking for?
I think that helps with the design trades. I'm looking to improve my heating/cooling efficiency next (I have PV) but it can be very expensive especially since I have a 75 year old house with lots of doors/glass.
I use both microinverters and centralized inverter. I'm somewhat agnostic on which to go with for a new system. I've had component failures with both. The big advantage with microinverters, I find is with expanding the system; total freedom for panel type and power.
Please keep us posted!

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Re: Ideas: Solar PV, Radiant Thermal for Major Renovation

Sun Feb 02, 2014 11:51 am

Im putting a room addition on now and expanding an existing solar PV system. My thoughts on roofing is to use the cheapest stuff available under the solar panel since this area is covered. Theinstallers will love you as it is easier to mount the frame rails. My first system was installed over a concrete tile roof and we encountered a lot of problems with broken tiles. These tiles continue to give me problems whenever I go on the roof to clean the solar panels.

Since your remodeling you can hide the electrical lines, I have ugly electrical conduit running down my walls.

I'm in the San Diego area and my roof is also not insulated, but the attic floor is. I noticed that the attic space got a lot cooler after the PV system was installed. All those panels shading the south facing roof made a noticeable difference, both in the attic and in the house.

If you have an in obstructed view, i.e., nothing shading your panels, I'm not sure going with micro inverters is worth the additional cost.

If I had a pool I would use solar to heat the water supplemented by the existing gas heater. A heat pump is expensive and I believe its operatings costs are more than heating with gas.

Because of the amount of power the solar array was producing, I elected to go with a heat pump for heating and cooling in my house. The A/C function works well but the heat function has a characteristic I don't like and that is the temperature rise in the air coming out of the system feels cold compared to my previous gas fired furnace. It still warms the house fine but the cooler air is an issue. This problem get worse on cold nights (for us in SoCal, anything below 40). If I had a pool I would liked to pull heat from the pool for the heat pump. So instead of doing a heat exchange with 40 degree outside air you can use pool water that is a lot warmer. I think this would help resolve the drafty heat pump issue.

During the year I run the A/C on only a few days. The rest of the time I simply open the windows. On hot nights I run a whole house fan. The fan was a relatively cheap item that works extremely well to cool the house to the outside temperature. I also use ceiling fans to turn slowly in the bedrooms to keep the air from becoming stagnant.

Getting rid of the crappy single pane windows and replacing with high performance insulated glass made a huge difference in my house. The new windows not only look a better bit the cold drafts that we used to have to live with are gone. I also changed my wooden outside doors with one that were better sealed.

Using CFL and LED lights for general lighting saved a lot of power that I could use for better things like an EV. I still use incandescents where the color and light spectrum is important, like over the dinning room table.

I'm not an expert, but these are some of the things I did that seem to work. Good luck on your project.

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Re: Ideas: Solar PV, Radiant Thermal for Major Renovation

Sun Feb 02, 2014 8:35 pm

Although more expensive, metal roofing shd last for the rest of your life. With the PV clips onto the standing seam, there is no puncture of your roofing material for water intrusion. For us, we are into rainwater catchment, so prefer water without all the grit and gravel from asphalt shingles. Also, not having to think about re-roofing (hopefully ever) is another plus. Amortized cost over time makes metal roof attractive.

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Re: Ideas: Solar PV, Radiant Thermal for Major Renovation

Sun Feb 02, 2014 8:41 pm

JimSouCal wrote:SOLAR
The use of micro inverters appeals to me because of the redundancy, elegant failure, but I'd be open to a persuasive argument for a straight DC system with a main inverter.
Micros have lots of advantages. All I can think on the central inverter would be you could service or replace the inverter yourself much easier if it is on ground level.
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Re: Ideas: Solar PV, Radiant Thermal for Major Renovation

Mon Feb 03, 2014 4:05 pm

Look into PassivHaus/Passive House. Incorporating even some of the passive house techniques in your renovation can reduce your need for heating, cooling, and electricity - making your choices there less critical and much less expensive. Even if you don't work toward certification, using the tools can help you optimize insulation, select windows, and defeat thermal bridging. Consider adding a cistern and capturing water from the metal roof. If considering it for drinking, verify the metal roof coating doesn't contain lead or heavy metals that will leach over time.

Good Luck - and enjoy the process!

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