Just finished my solar water heater 2 days ago... (Image heavy)

[Madscientist267]

Ok I was a somewhat ill-conceived, but basically, part of your system at least employs what I was getting at, kinda-sorta, with the exception of the water leaving the tanks for the panels/hydronic heat.

My thinking involved just the exhaust loops and DHW heat loops. Wondering viability with no water ever leaving the tanks (just coils).

Two questions with the layout:

Are there any 'anti-mixing' devices in place for the panel/hydronic loops at all? I know you said you couldn't (and wouldn't) modify the tanks internally, but maybe velocity reduction as the water enters the tanks?

The other is, what are the two 'kinks' in the red recirc line as they go 'past' the panel lines?

EDIT - Wastegate radiators?

Steve

[rossw]

Ok I was a somewhat ill-conceived, but basically, part of your system at least employs what I was getting at, kinda-sorta, with the exception of the water leaving the tanks for the panels/hydronic heat.

My thinking involved just the exhaust loops and DHW heat loops. Wondering viability with no water ever leaving the tanks (just coils).

In summer, when there's no hydronic floor heating, and (until recently) no solar input, the system operated that way, quite sucessfully.

Two questions with the layout:

Are there any 'anti-mixing' devices in place for the panel/hydronic loops at all? I know you said you couldn't (and wouldn't) modify the tanks internally, but maybe velocity reduction as the water enters the tanks?

Anti-mixing for the solar collector works by virtue of quite low flow rates, comming inside on 1/2" PEX, then through expansion to 1.25" several inches before it gets to the tank. Its velocity is quite low.

The hydronics return comes in well down the tank, where I actually want it to circulate and mix, so I can get some cool water down to and around the generator loops. *SO* many things I'd do differently given the time again.

The other is, what are the two 'kinks' in the red recirc line as they go 'past' the panel lines?
EDIT - Wastegate radiators?

LOL. No, it was my pathetic attempt at saying "this pipe does a cooks tour past the kitchen and all 3 bathrooms before returning" - there's probably 150 to 160 feet of pipe in that run. Each bathroom has its own tempering valve, so even in winter, hot water rarely takes more than a few seconds to reach the tap or shower (as long as the circ pump has been running!)

I'll be sure to make that more evident in the next drawing    (Along with adding things like where the temperature sensors are, and pressure gauges, sensors, flowmeter, expansion tanks, the GSHP input and loops, etc!)

[Madscientist267]

Hmmm... ok I was wondering why it kinda just 'shorted out' and went back to the tank. LOL

So if I understand this correctly, the DHW supply circulates 'all of the time' so that hot water is always readily available at the taps?

I like the idea, if this is indeed the case, except for one thing... what about heat loss?

On second thought, that can't be right tho. Am I missing something?

The recirc pump would only bring the heat to the taps, but I don't see anything to pressurize it.

Maybe I should wait for the 'better' diagram... LOL

Steve

[rossw]

Hmmm... ok I was wondering why it kinda just 'shorted out' and went back to the tank. LOL
So if I understand this correctly, the DHW supply circulates 'all of the time' so that hot water is always readily available at the taps?
I like the idea, if this is indeed the case, except for one thing... what about heat loss?
On second thought, that can't be right tho. Am I missing something?
The recirc pump would only bring the heat to the taps, but I don't see anything to pressurize it.
Maybe I should wait for the 'better' diagram... LOL

The recirc pump is controlled by the rest of the home automation stuff (which helps me get the most "liveability" out of things, and tries to keep power use to a minimum - things like automatically turning on and off lights in rooms based on when people are in there, only running pumps when required etc. The recirculating pump runs in time windows. We don't usually shower at 3am for example. The system runs the pump between 6am and 9am, and again from 5:30pm to 10pm. Not shown is a temperature sensor  that measures the return temperature and only runs the pump as much as is necessary to keep the water "warm enough".

The pipes are all well insulated, heat loss isn't a major issue. If we're not drawing water off, the temperature has no discernable drop after circulating for 3 hours.

As for pressure - thats the trick! The hot water lines are permanently at the cold water supply pressure. You will see where the hot water comes back from the recirc pump, going to two ball valves - one to each tank heat exchanger - there is also a line there from the domestic COLD water supply.

When any hot tap is turned on, cold water flows from the cold supply into the "cold" side of the heat exchangers. The NRV by the recirc pump prevents it cheating and rushing up the hot pipe backwards, so cold water is drawn through either/both DHW heat exchangers and along the line to get to a tap, and the recirc pump can just move water around the hot pipes the rest of the time. (Its just a small pump, runs perhaps 10 litres/minute)

[Madscientist267]

Wow ok gotcha.

That little blue leg next to all the red lines... missed it somehow...

I figured you had some kind of time windowing system, although didn't really think about the thermostat to control the pump.

More or less thats what I meant by 'all the time' with the quotes; really should have read 'whenever needed'. I would have actually been a bit shocked if it were otherwise, knowing how much juice a water pump can use.

I like it. Addresses the need for that instant hot water thing. Form AND Function.

I wonder if that would be a viable solution in an 'average' home (one that isn't even using solar etc)... Although probably not cost effective to implement after the fact (read 'once built'). I have two locations in my house that take FOREVER for the water to get hot at the taps, and go figure, they're in two of the most used locations - the kitchen and the master bath... W  T  F  ?!

Unfortunately, this is why I wanted to design my own house. To be able to address things that typical designers and builders just look at as 'they will just have to deal with it'... 

We're looking at installing two of those 'instant' water heaters at these locations to help with this, but I still plan to offset the overall DHW issue with a system based loosely on what you guys have been sharing here.

This is good stuff!

Steve

[rossw]

That little blue leg next to all the red lines... missed it somehow...

That's the one

I would have actually been a bit shocked if it were otherwise, knowing how much juice a water pump can use.

The little pump takes about 20 watts (from memory).

I wonder if that would be a viable solution in an 'average' home (one that isn't even using solar etc)... Although probably not cost effective to implement after the fact (read 'once built'). I have two locations in my house that take FOREVER for the water to get hot at the taps, and go figure, they're in two of the most used locations - the kitchen and the master bath... W  T  F  ?!

I looked at this once for someone else. Depending on how your place is hooked up, there is a possible (and cost effective) way to retrofit it.
At the far end of the run (or as far as is practical), you put a recirculating pump and a non-return valve (check-valve) from the hot line to the cold line.
The pump in this case will NEED a timer and/or a thermal switch. You turn the pump on and pull hot water down your (insulated) hot water line, and "push" it into your cold water line. Keep going until you "see" hot water arrive at the pump - then your hot line is "charged".
This will only work if there are no other check-valves in your cold line before it can get back to the water heater, obviously! (And for obvious reasons, you'd only do this with a mains-pressure water heater, YMMV, caveat emptor, etc, etc)

[spinningmagnets]

This is a great thread! I would like to suggest a couple possible options that might be helpful for a similar future build. As far as the glazing-to-water-volume rule. I believe its good to have as big a collector as possible for the maximum winter harvesting, when the heat is needed most. It may be disregarded by some as overglazing, but in the summer some portion of the collector can be temporarily shaded.

Most RE enthusiasts seem to feel that the only viable options should have no input at all by the home-owner. I don't want a fussy system as much as anyone else, but manually adjusting a partial cover a few times a year shouldn't be too unreasonable. A cleverly designed shading option can also add a level of protection during storms (we have significant hail and frequent wind-blown debris here in Kansas).

My second suggestion for consideration may have some problems I hadn't thought of, so I hope to get some input (happy to hear good or bad). I think it may be beneficial to possibly have two stratified regions by having the hottest part of the thermal storage be an upside-down insulated cup in the center of the larger mass.

Heat rises, and the hottest water from the collector could be inserted into the storage at the top of an open-bottomed central sub-storage area. Though its also insulated, any heat that dissipates outward simply goes into the larger (and cooler) water mass. Of course the larger mass has the 4" insulated sides and top. Bulkhead fittings can be used since leakage (if any) would only pass to another water region in the tank.

During the winter, when the overall mass was cooler than desired, the central storage would still be as hot as possible. This dual zone storage also allows the medium-grade heat to be used for radiant floor without lowering the high-grade section, which would presumably be used to heat the DHW coils.

I got the idea from reading about the anti-backflow-at-night Trombe wall at builditsolar. Thoughts?

[Madscientist267]

Something also came to mind for me about this...

We do it all the time electrically, but I'm not really seeing much about it here: Dumping!

A small radiator that can be set up with flaps (or even valves, or both?) to prevent heat loss when its not intended, but allow the system to get rid of surplus (read 'dangerous') temperatures when production is high.

This particular flavor of RE has to be the cheapest there is in terms of production costs, I mean how does it get much cheaper than some copper in a box with some glass on it?

Considering that extra square footage for collector space would add so much in terms of recovery and/or load capacity, why not just dump what isn't needed and be done with it?

I'm not saying 10 ft/gal or anything equally ridiculous, but 3 or 4, or even 5 if someone were so inclined wouldn't be all that much more money considering the bang per buck. In terms of overall system cost, I would think that double the collector wouldn't be like double the PV - system cost would probably only go up by a couple dozen percent, and the hot water would just 'be there' regardless of what is going on outside. All but for maybe the most extreme climates...

Just a thought...

Steve

[rossw]

Something also came to mind for me about this...

We do it all the time electrically, but I'm not really seeing much about it here: Dumping!

A small radiator that can be set up with flaps (or even valves, or both?) to prevent heat loss when its not intended, but allow the system to get rid of surplus (read 'dangerous') temperatures when production is high.

I've always had this setup, because my hot water was (originally) heated entirely from the waste heat from the generator. As such, I couldn't control the amount of heat I got. When we needed it, the generator HAD to run. No if, but or maybe. If (as happened back then) we had poor sun and wind days for days and days on end (like when we had major bushfires and smoke was so thick we never saw more than a dull red glow from the sun), the generator ran a lot. And being summer, we didn't need the heat in the floor, so the tanks got hot. Then very hot.

My GSHP loops (1.6km/1 mile) of 1" HDPE burried 3m underground were designed to get cheap heat OUT of the ground in winter, but also work great to dump excess heat into the ground in summer.

Also, because of the (quite low) ground temperature, you don't need much flow to dump a very substantial number of BTUs this way!

[Madscientist267]

Think it's practical for a system where the only input is purely solar?

When I do mine, I probably won't include an ICE generator in the mix, mainly because the genny I have is already established and is air cooled. It hardly ever gets run, and honestly I burn more gas just keeping it clean than I do for real world production (read 'emergencies') - I'm not off grid by any means. It's there to run the fridge primarily when the grid goes down, and to run space heaters in the winter during the same. Not much more. Probably could handle one of the A/C units if things were desperate...

So in my case, I would only be dumping the extra collector input.

I guess I should reword the question, as I can clearly see that it would be practical. What I really want to know is, what would be the sweet spot for the ratio of collector to storage with such a layout?

Going by what I like to see with the PV that I have, psychologically, I am 'happier' the more the dump load is dumping. Something about knowing that the juice is there no matter what. For water, I'd really like to see the same thing. As I mentioned before however, I wouldn't be so inclined to design a large scale PV system this way. The margins would be much tighter due to the cost of the panels.

But for DHW? Why not?

I won't be able to dump into the ground; the cost of doing so would be prohibitive in my situation. I will probably be stuck using something like an engine radiator (typical car comes to mind) to waste the excess.

One thing worthy of mention - I would not be using it for space heating (just yet), although with the radiator design I could set up a set of damper boxes and route the heat inside if I felt froggy enough for the winter months.

Am I pretty close in guessing around 5ft/gal? Or higher? Is 10 worthwhile to consider so that even winter means there is always plenty of hot water available (just as it is on-grid)?

My guess is 5 sq ft... ?

Steve

[rossw]

Maybe I should wait for the 'better' diagram... LOL

Replaced the old image with an updated one http://fieldlines.com/board/index.php/topic,145454.msg990827.html#msg990827

[jondecker76]

Its been a while since I posted and thought that I would give an update.

I originally planned to track things a lot better than I have, but its been a busy year!

Since I put the system online in Mid may, I have been in absolute awe of this system's performance.
I now have 3 electric bills in a row where over $100 per month has been shaved off! (I have a family of 6 and we use a lot of hot water. Also note, that at the same time I sold our air conditioner, and made boxes with fans in them that pull cool air into the house from the basement - I estimate $40-$60 per month savings from the solar hot water its self). Since being put online, it has provided 100% of our hot water (the tank has not dipped below 125 degrees since initially heating up past this point)

My tank is normally around 140 degrees F, and I have let it get as high as 166 degrees.  The 230 Gallons gain about 20-25 degrees of temperature on a good day.  Our daily hot water use usually takes about 5-10 degrees from the tank, and we loose about 4-5 degrees through the insulation - so the system is balanced very well with our hot water usage (every time I'm near max tank temperature, I get a cloudy stretch of days that bleeds the temperature back down).  I have had several times where we had 3-4 days of no sun and there was enough buffer in the tank to get through these cloudy days without the tank temperature falling below 125 degrees.

The max output I've seen from the unit is just a bit over 13,000 BTU/hr.

Here are the BTU output for each month so far:
May: 477,773 BTU
June: 688,220 BTU (June was unusually coudy this year)
July: 904,332 BTU
Aug: 1,103,389 BTU

[GaryGary]

Its been a while since I posted and thought that I would give an update.

I originally planned to track things a lot better than I have, but its been a busy year!

Since I put the system online in Mid may, I have been in absolute awe of this system's performance.
I now have 3 electric bills in a row where over $100 per month has been shaved off! (I have a family of 6 and we use a lot of hot water. Also note, that at the same time I sold our air conditioner, and made boxes with fans in them that pull cool air into the house from the basement - I estimate $40-$60 per month savings from the solar hot water its self). Since being put online, it has provided 100% of our hot water (the tank has not dipped below 125 degrees since initially heating up past this point)

My tank is normally around 140 degrees F, and I have let it get as high as 166 degrees.  The 230 Gallons gain about 20-25 degrees of temperature on a good day.  Our daily hot water use usually takes about 5-10 degrees from the tank, and we loose about 4-5 degrees through the insulation - so the system is balanced very well with our hot water usage (every time I'm near max tank temperature, I get a cloudy stretch of days that bleeds the temperature back down).  I have had several times where we had 3-4 days of no sun and there was enough buffer in the tank to get through these cloudy days without the tank temperature falling below 125 degrees.

The max output I've seen from the unit is just a bit over 13,000 BTU/hr.

Here are the BTU output for each month so far:
May: 477,773 BTU
June: 688,220 BTU (June was unusually coudy this year)
July: 904,332 BTU
Aug: 1,103,389 BTU

That sounds great -- thanks for the report.

Gary

[Madscientist267]

Agreed - I'd say that its a success...

Going to have to do this. And soon.

Steve