Buying a house with passive solar hot water

[Grabcon]

The wife and I are buying a house with passive hot water solar for domestic hot water. We have not closed so I don't have access to answer detail questions. The owner has passed so asking questions will not happen without a ouija board. I have a couple of photos and a drawing that I think describe the system. What I would like to know is how this system is plumbed does it make sense? Will or does it work? Is there suppose to be an expansion tank somewhere?

The drawing is a best guess based on photos.

 

[Rocketman]

I don’t really know much about solar hot water - other than I think it’s cool (or maybe NOT cool ?).

From your drawing it looks like the solar just “pre-heats” the water before it goes into the water heater. Is that the case or are there some pumps or something that circulate the warm water back to the roof to heat it to HOT. (Which is the way I always thought solar hot water worked. (See told ya I don’t know much).

One thing that could help is get the owners manual for each item to make sure you understand what it does and why it is there.

Also is there a plumbers business card attached anywhere? You may want to ask if anyone knows who installed it? DIY or a plumber?

Also what area (state) are you in? Does it freeze in your area?

Good Luck

 

[Meshdish63]

I agree with Rocketman in that the system is preheating the water before it goes into the water heater. On a sunny day the water in the panels could be 150+ degrees just from sitting there, similar to water sitting on a garden hose laying out in the sun. The water is going to expand at those temperatures so installing an expansion tank might be a good idea.

I suggest posting your question over here,

BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution

Build It Solar will help people with Do It Yourself skills build solar projects that save money and reduce pollution. It is a "hands-on" site with detailed plans for solar projects including solar space heating, water heating, passive solar home design, solar pool heating, solar cooking...

builditsolar.com

 

[Grabcon]

Thanks, but as far as documentation the place is empty. Myself and the inspector did not see any electric or pumps to the solar water. Like I said in the opening I will just have to wait until closing for further details.

 

[Sky-HHI]

Why do you think you need an expansion tank on the system? There is not an expansion tank on a regular water heater and they can get over 150+ degrees. I grew up in south Florida and many homes has the same kind of system to take advantage of solar to preheat the hot water.

 

[houseofancients]

Why do you think you need an expansion tank on the system? There is not an expansion tank on a regular water heater and they can get over 150+ degrees. I grew up in south Florida and many homes has the same kind of system to take advantage of solar to preheat the hot water.

there should always be an expansion tank and safety value on a hot water heating system ...
that hotwater tank can actually become a pretty dangerous bomb when put under pressure

 

[Grabcon]

"Why do you think you need an expansion tank on the system?"

Don't know hence the question. I am unfamiliar with hot water solar and need to understand requirements and how they work. So it is just a simple question. But there also is a capped stub on the piping system that makes no sense.

Hot water heating systems do have expansion tanks. Maybe that is where my question arises from.

Sky-HHI a question for you. The system the nearest I can tell uses domestic hot water through the solar panels and pushes the heated water into the electric HW tank when the system calls for water. If the system is idle (no call for hot water) what happens to the hot water being heated by the solar panels? Does the water just sit in the system and passively re-circulate or doesn't move at all? I currently don't see any bypass piping for that to happen. Until I take ownership and get on the roof I will not be able to look for a bypass of some sort.

 

[Grabcon]

Relief valves (safety valve) on hot water tanks are a must as if the relief is plugged or fails the results are catastrophic. All tank hot water heaters come with a relief valve. I have never had a home with an expansion tank on the domestic hot water Supply, only on a home with a hot water heating boiler system.

 

[OffGridInTheCity]

Expansion tanks allow for expansion of the hot water. They're small versions (like 2 gal) of what you use with a well pump (like 50gal) that absorb water pressure and let it release in a controlled way. Without it, you can get leaks as pressure can spike in the pipes from the water heating up.

Here's a random example from Home Depot....

Everbilt 2 gal. Thermal Expansion Tank EF-TET-2T - The Home Depot

Built with heavy-duty butyl diaphragm system to absorb the expansion of water volume and help prevent dangerous pressure build-up. This Everbilt Expansion Tank will absorb pressure increases when properly

www.homedepot.com

• Butyl diaphragm system absorbs the expansion of water volume

My original plumbing (home built in 1997) on my LG water heater didn't have one. This might be why you're prospective home doesn't have one. I added one when I replaced the water heater a couple of years ago with a heat-pump version.

 

[Sky-HHI]

Never mind

 

[efficientPV]

Many homes have a check valve by code so water doesn't drain back if the mains lose pressure. If someone isn't using water periodically pressure builds up in the tank and small amounts drip out the TP valve. Those water systems with mineral content form scale on the seals and eventually just keep leaking. There are people who just put a pipe plug in then. Solar hot water goes thru vast temperature changes and pressure builds up. I have a PV water heated tank in garage for laundry and I have to periodically relieve pressure. I do have a really tall 3/4 inch pipe for expansion but it isn't enough. You are not really going to explode, but water solenoids in washers etc can be damaged.

 

[nofossil]

Drain back solar systems have no pressure, because the water ( no coolant needed) drains by gravity ( after the pump shuts off) to a small holding tank. A pump pulls water out of the holding tank when the sun shines. If that’s the type you have you definitely don’t need a pressure tank

 

[Grabcon]

Drain back solar systems have no pressure, because the water ( no coolant needed) drains by gravity ( after the pump shuts off) to a small holding tank. A pump pulls water out of the holding tank when the sun shines. If that’s the type you have you definitely don’t need a pressure tank

I will find out on the 11th, but I believe this is a closed loop system and no pump. Something similar to the attached diagram.

 

[dobrzpe]

just curious: are you in a climate where there is NO CHANCE of freezing? like, at ALL? just wondering b/c my hydronic system uses glycol in the loop... then there is a heat exchanger in the hot water tank. so it's a closed loop. i couldn't quite tell from your pics...