Need help and advise on designing a hot water system.

[inhotwater]

Hello Solar enthusiasts,

I am looking for guidance in designing a solar water heating system, for domestic hot water and house heating.

My details are: I'm about 100 miles north of San Francisco, one mile from the coast and just outside of most of the fog, mostly sunny but still cool. I have a good size grid tie PV system that I installed in 2001 and supplies pretty much all my electricity needs for a good size mostly all electric house.

What I want to do, is produce hot water for (1) take most all the load off my electric water heater, and (2) provide heat for my house, which will be pumped into the lower story of the house, to be absorbed into a large mass of concrete. I am doing this now on a smaller scale with hot air pumped to the lower level and it works quite well, but I would like to expand this.

I am a retired General Engineering Contractor, with the tools and ability to successfully undertake a project like this, I just am having a hard time finding the information and help I need to design the system.

I have some of the components, but will need to purchase much of the needed parts. What I have is 8 3x7 Grumman copper tube type collectors, and a variety of pumps, that may or not be suitable for this project. My current water heater and pressure tank are ready for replacement and repositioning so most everything with the exception of the panels will be new. The panels are in nice condition, pressure tested for 24 hours, yesterday I did a heat test at about solar noon, I measured an output from one panel, of one liter of water, heated 45 degrees in 45 seconds. The water in the panels also got up to about 210 degrees when left still for a little while.

The site for the panels is about 75 feet away and 8 feet above where the water/ storage tank will be.

I want to build a system that is both robust and uses as little electricity as possible, as I am hoping to use the electricity saved by heating water, to run a heat pump for house heat, so someday I can stop burning firewood as my main cold weather heat source.

Some of my questions are:

How do I figure what pump capacity I need an what type.

What are my options for controllers and pump stations.

Do I want a prepackaged pump station or individual components for a system like this.

And many more.

Thanks in advance.

[SunEagle]

Hello inhotwater and welcome to Solar Panel Talk

You are able to make new posts but there may be an issue with some characters that the forum software doesn't like so it cuts off your post.

[inhotwater]

Hello inhotwater and welcome to Solar Panel Talk

You are able to make new posts but there may be an issue with some characters that the forum software doesn't like so it cuts off your post.

It's just plain text, can I Pm or email you the contents to see if you can determine the issue?

[Logan5]

retype your prepared text directly into the SPT forum editor, Do not cut and paste from a file created with another editor.

[inhotwater]

retype your prepared text directly into the SPT forum editor, Do not cut and paste from a file created with another editor.

Thanks, that worked.

[Mike90250]

What is your freezing/frost risk ?

i'd suggest using glycol in the collectors at ground level. and let it thermosiphon to an elevated , insulated hot water tank with a heat exchanger. Then you use a small (1/10HP) circulation pump to send the hot water wherever you want it.

You want to design a system where the collectors will not stagnate (if power goes off and pump stops). If the collector circulation stops, you start boiling water in them and that's not good.
You want the glycol antifreeze, because freezing the collectors at dawn (radiative cooling effect) is also bad for the plumbing. The hot water tank is not likely to freeze with a couple hundred gallons in it.

[J.P.M.]

If you really want to do this in a professional and thorough way, you'll need to educate yourself. Start with "Solar Engineering of Thermal Processes", Duffie & Beckman. That's still one, and probably still the best solar thermal bible around. This isn't meant as a knock, but you need an education before you go further. Without one, you'll be wasting your time. I've been around solar thermal since the mid '70's and made it work in very cold climates for space and domestic water heating. The way you describe what you've done only reinforces my opinion you need the education.

After that, and before you begin design, you need to understand what thermal loads and duties loads you intend to address with the solar thermal. While doing that, you'll also learn that conservation and load reduction are just about indispensable first steps before offsetting the remaining (and smaller) loads. One small example: keeping the energy source as close to the point of use as possible is nearly essential making that 75 ft. run something to be addressed and eliminated at the outset.

Most of the stuff I cut my teeth on and in some cases contributed to are mostly out of print. Some additional titles besides Duffie & Beckman you may find useful:

1.) Lunde, "Solar Thermal Engineering", ISBN # 0-471-03085-6. Wiley, 1980.
2.) Kreider, "The Solar Heating Design Process", ISBN # 0-07-035478-2McGraw-Hill, 1982
3.) MASEA, "Home Remedies", ISBN # 0-9601884-0-1, self published, 1980, and probably out of print, but scrounging around E-bay/the net you may be able to root out a copy.

#3 is selected presentations from the 1st national retrofit conference which I attended. Lots of common sense from the golden age of tree hugging.

Also, don't forget you'll need the imprimatur of at least the local AHJ for a lot of what you'll be attempting.

I know the above is taken by some as preaching. Take it for what it's worth, but if nothing else, walk in with your eyes open.

Good luck.

[inhotwater]

What is your freezing/frost risk ?

i'd suggest using glycol in the collectors at ground level. and let it thermosiphon to an elevated , insulated hot water tank with a heat exchanger. Then you use a small (1/10HP) circulation pump to send the hot water wherever you want it.

You want to design a system where the collectors will not stagnate (if power goes off and pump stops). If the collector circulation stops, you start boiling water in them and that's not good.
You want the glycol antifreeze, because freezing the collectors at dawn (radiative cooling effect) is also bad for the plumbing. The hot water tank is not likely to freeze with a couple hundred gallons in it.

Mike,
Freezing/frost risk is small here, and declining rapidly, but there are always surprises and are especially bad here because so many systems and machines are unprepared that when we do get a hard freeze, (last one was about 20 years ago) lots of stuff is destroyed, plumbing, machinery, etc. I will use glycol in the collector loop.

Your suggestion to thermosiphon from the collectors is interesting, don't know if it would work for the direct heat from the panels to the house, but might work really well as a fail safe for pump/power failure and to get rid of extra heat. The location of where I need to put the panels, also would work well with a thermosiphon for that purpose.

[inhotwater]

If you really want to do this in a professional and thorough way, you'll need to educate yourself. Start with "Solar Engineering of Thermal Processes", Duffie & Beckman. That's still one, and probably still the best solar thermal bible around. This isn't meant as a knock, but you need an education before you go further. Without one, you'll be wasting your time. I've been around solar thermal since the mid '70's and made it work in very cold climates for space and domestic water heating. The way you describe what you've done only reinforces my opinion you need the education.

After that, and before you begin design, you need to understand what thermal loads and duties loads you intend to address with the solar thermal. While doing that, you'll also learn that conservation and load reduction are just about indispensable first steps before offsetting the remaining (and smaller) loads. One small example: keeping the energy source as close to the point of use as possible is nearly essential making that 75 ft. run something to be addressed and eliminated at the outset.

Most of the stuff I cut my teeth on and in some cases contributed to are mostly out of print. Some additional titles besides Duffie & Beckman you may find useful:

1.) Lunde, "Solar Thermal Engineering", ISBN # 0-471-03085-6. Wiley, 1980.
2.) Kreider, "The Solar Heating Design Process", ISBN # 0-07-035478-2McGraw-Hill, 1982
3.) MASEA, "Home Remedies", ISBN # 0-9601884-0-1, self published, 1980, and probably out of print, but scrounging around E-bay/the net you may be able to root out a copy.

#3 is selected presentations from the 1st national retrofit conference which I attended. Lots of common sense from the golden age of tree hugging.

Also, don't forget you'll need the imprimatur of at least the local AHJ for a lot of what you'll be attempting.

I know the above is taken by some as preaching. Take it for what it's worth, but if nothing else, walk in with your eyes open.

Good luck.

J.P.M.

I ordered a copy of Solar Engineering of Thermal Processes.

The 75 foot run from the panels to the tank/ pump station is the total length piping and really can't be shortened, it's the only spot with good sun all year, and enough room for all the panels. I see large arrays on apartment buildings that must have much longer runs and would like to know how they are designed.
I understand the need for load reduction first, and right now, most of my heating is from a simple system of pumping hot air down from the roof, first to the main floor, then through a thermostatically controlled diverter, to the lower level, where is is absorbed into concrete, this works well, and keeps the house warm for several days of cold cloudy weather, but there is capacity for much more heat storage there, otherwise I use about a cord or less of fire wood each year, and have basically no electricity bill.

I know I have a lot to learn, am willing to take advise and do my homework, I'm in a fairly rural area, water heating and other solar energy systems are not common around here, so to make sure I have and can keep running a good system, I am pretty much on my own.

[Mike90250]

Thermosiphon, done right, gives you a nice passive system. With pumps, if the power goes off, you boil the system dry

[J.P.M.]

J.P.M.

I ordered a copy of Solar Engineering of Thermal Processes.

The 75 foot run from the panels to the tank/ pump station is the total length piping and really can't be shortened, it's the only spot with good sun all year, and enough room for all the panels. I see large arrays on apartment buildings that must have much longer runs and would like to know how they are designed.
I understand the need for load reduction first, and right now, most of my heating is from a simple system of pumping hot air down from the roof, first to the main floor, then through a thermostatically controlled diverter, to the lower level, where is is absorbed into concrete, this works well, and keeps the house warm for several days of cold cloudy weather, but there is capacity for much more heat storage there, otherwise I use about a cord or less of fire wood each year, and have basically no electricity bill.

I know I have a lot to learn, am willing to take advise and do my homework, I'm in a fairly rural area, water heating and other solar energy systems are not common around here, so to make sure I have and can keep running a good system, I am pretty much on my own.

Understood. Get the basics of fluid mechanics and heat transfer down first, then the basics of the solar resource as in solar geometry and resource availability. Without those building blocks you'll spend a lot of time wondering what you're reading means. The rest will fall into place from those building blocks. Without them, it'll just take longer to get it close to safe and right.

[LucMan]

First do your research.
Then focus on drain back systems. They are the simplest high output systems that are not likely to freeze or overheat, low maintenance and no glycol required. One large pump or 2 smaller pumps in series can be used. No need for pump stations, purge valves, expansion tanks, etc.
After you are educated on solar thermal come back and you can get all the help, hints, and recommended equipment on this site.
Good luck

[inhotwater]

I got and read, Solar Engineering of Thermal Processes, I also ordered a copy of The Solar Heating Design Process by Kreider, and will read that as well.

The Drain back systems are looking pretty interesting, are there any issues from thermal shock, when filling the collectors, when the sun is on them and the collectors are hot?

[J.P.M.]

I got and read, Solar Engineering of Thermal Processes, I also ordered a copy of The Solar Heating Design Process by Kreider, and will read that as well.

The Drain back systems are looking pretty interesting, are there any issues from thermal shock, when filling the collectors, when the sun is on them and the collectors are hot?

Thermal shock: Avoid abrupt changes in conditions, particularly fluid flow rates and temperatures. Bad things can happen when the equipment is not capable of keeping up with the rate of change of conditions.

One more suggestion: a good, basic heat transfer text. McAdams is one of the bibles, Kreith is another. FWIW, Kreith was also one of my early solar mentors.

[inhotwater]

Thermal shock: Avoid abrupt changes in conditions, particularly fluid flow rates and temperatures. Bad things can happen when the equipment is not capable of keeping up with the rate of change of conditions.

One more suggestion: a good, basic heat transfer text. McAdams is one of the bibles, Kreith is another. FWIW, Kreith was also one of my early solar mentors.

Which books by McAdams and Kreith do you recommend?