Please critique domestic hot water plan

mike95490 · January 2012

All,
Asking for some advice on what I want to be "self managing" low energy, domestic hot water system. Off grid, so electrical consumption reduction is very important.

Let me explain the layout of the attached sketch (.jpg)

Cold water would first enter a heat exchanger loop, in the flue, above the secondary combustion chamber, of a site built masonry heater. http://www.tempcast.com/ The loop is 3/4" SS high pressure pipe, installed a few degrees off horizontal (to initiate thermosiphon) it would connect to insulated hard copper pipe, and travel to a 2nd floor, 85gal storage tank, located nearly directly above the heater.
The proposed tank looks like it may be a RHEEM Marathon Thermal Storage Tank #MTS852000. It is a plastic (polybutene & filament wound fiberglass, 170F limit) tank with a layer of insulation (R value not stated) and an outer plastic shell, it also has several ports in different areas. Manual at:
http://globalimageserver.com/fetchDocument.aspx?id=7db02d15-1283-4cdf-a3fe-7ab73aac67e3

In the winter, I've been told, each firing of the masonry heater, can be expected to transfer 30,000 BTU to the water loop. The heater can only be fired 2x a day, 12 hours apart. I calculated that 30K BTU into 85 gallons would be a 44F rise of the tank temperature, per firing. Right ?

I believe, with 45 bends, and not 90 elbows, this would self-thermosiphon. Anyone know how to verify this, before it's built, and found not to? I don't want to have a circulation pump if I don't need one.

Then, this tank-o-warm water, would feed the inlet of a rooftop solar water heater, which in cloudy winters, not provide much gain, but I'll take what I can get. It could be bypassed if it looses too much heat, or hopefully, a bit of gain is to be had. The Rheem Solaraid rooftop unit is supposed to have some sort of high temp valve (according to the plumber) that "burps" a slug of too hot water, to keep it's temperature within limits.

Output of this, finally, feeds the high efficiency, tank-less water (which has a 2 gallon tank in it) and a 2nd generation controller, supposed to deal well with any inlet water temps, and prevent the "cold-slug-o-water" in the middle of your shower.

Then the faucet recirculating hot water scheme, with a return line run from the most remote faucet. Some brand of pump. Taco is mentioned a lot. Grundfos and Wilo also supposed to be OK. Taco has a "D-Mand" system with timer, thermostat, remote. Who makes a good pump, that's easy to rebuild ? Taco, Grundfos, Wilo ? Magnetic coupling - pro/cons? Bronze vs. SS ?
Taco has a $30 "aquastat" for cycling the pump off/on after the timer kicks it on, so once the pipe heats up, it can save a few watts. Any idea if these work reliably, or if they are always failing.

Open system, no inlet check valve, about 70psi water pressure, fed from elevated tank.

So, there is a bunch of questions, and I hope to get some critique and/or advice, before I go down the wrong path too far.

Thanks, Mike
Attachment not found.

niel · January 2012

Re: Please critique domestic hot water plan

hi mike,
i'm not an expert with water systems, but i do know that the solar collector could wind up being a good radiator of heat too. at least one of your masonry heater cycles will be in the dark of night so the heated water passing through the solar heater could radiate the collected heat. i think the solar collector would normally best serve by being placed in the masonry cold water return as a preheater to the masonry heater, but when the masonry heater is off the direction of flow in the masonry loop could reverse if installed wrong. i guess the easiest way to insure no radiation of heat through the unilluminated solar collector would be to have bypass plumbing to optionally take the solar collector out of the equation. if doing this manually this can be a pain in the butt and would get very complicated if done with automatic controls based on temperature. maybe on a timer would work, but could allow radiation through the collector on a cloudy overcast day after the masonry heater has been running.

mike95490 · January 2012

Re: Please critique domestic hot water plan

niel wrote: »

i'm not an expert with water systems, but i do know that the solar collector could wind up being a good radiator of heat too. ..

The rooftop collector has a closed loop heat exch that heats the storage tank, I think it's set up to not radiate at night, I hope, otherwise, it would always cool off. But I have considered possibly needing to bypass it in winter, if it proves to be loosing heat. I'd use a manual byapss valve, like a bypass for a watersoftener, and switch it over. I'd bettger go look that one up now too.

BB. · January 2012

Re: Please critique domestic hot water plan

One thing to always double check... Most hot water "devices" assume cold water input. If you feed pre-heated water into their cold water input, you may have problems melting a plastic dip tube etc.

-Bill

stephendv · January 2012

Re: Please critique domestic hot water plan

I haven't looked to closely at the thermal store, but if it can accept more connections, why not connect the solar directly to the thermal store - so you effectively have one central "battery" and multiple charging sources connected in parallel.

Thermosiphon on the masonry may not get the most heat out of it in a reasonable amount of time - no idea how to calculate this, but it would depend on how much flow you can get through the pipe. A circ pump would be able to heat up the tank quicker IMO - and they're very frugal these days with energy use.

westbranch · January 2012

Re: Please critique domestic hot water plan

Mike , a couple of quick thoughts from what I have contrived for our new place (in progress) I am planning on in floor heat so these may work for you.

1 use a drain back system so no fluid in solar heaters at night but in a closed loop system, will need a heat exchanger to isolate DHW
2 use a small pv powered pump to circulate fluid ( we have to be 50% glycol) sun in daytime pumps when the heater is collecting Btu's, self draining at sundown
http://www.oberread.com/Download%20Files/D5_Solar.pdf
3 rather than wasting hot water use an open pipe up to a reservoir placed higher than your collector.
4 keep heater fluids separate from house water - shut offs

hth
Eric

n3qik · January 2012

Re: Please critique domestic hot water plan

As for Taco pumps, have them for the past 30 years. Not one failure.

sawmill · January 2012

Re: Please critique domestic hot water plan

Mike
Some points you might want to consider for your DHW system. My limited experience with thermosiphon found it worked energy free, abeit very slowly. Once your furnace burns down and is radiating its stored heat through the masonry I don't know how efficient the thermosiphon would continue to operate? Since you would need very little lift a low wattage circ pump might be more efficient in the long run?

If this furnace has not been built yet, have you considered installing a metal storage tank within the masonry for direct transfer of heat with no pumps or thermosiphon involved. With bypass valves this pre-heat tank would only be used when fired, with the solar thermal taking over in moderate weather. With new construction it would be simple to make this tank accessible for service or replacement.

In respect with using wood heat I can speak from a lifetime of experience. If your combustion air is coming from the living area, cold outside air is being drawn in somewhere to replace it. Design your ash removal to be outside as it is almost impossible to remove ashes in your living area without some fogging. This is something you don't want to breathe especially if anyone has respiratory issues.

Keep in mind that it is impossible to burn wood and not have soot and creosote build-up in your flu. Some stoves will be better than others in respect to build up but you are still going to have it. Without flu maintenance there will have a flu fire in the future, the only question will be when.

I have had great success with Taco, these are great pumps.

westbranch · January 2012

Re: Please critique domestic hot water plan

Mike, Taco has a a warning on their replacement pumps NOT to mount it at the top of a tank. Excessively hot water, or steam, will soften some plastic parts, Impeller if I remember, anywhere else is OK, good pumps when mounted correctly.

n3qik · January 2012

Re: Please critique domestic hot water plan

The top of tank warning is due to air entrapment. These pumps do not purge air trapped in the impeller chamber that well.

SolarLurker · January 2012

Re: Please critique domestic hot water plan

I am by no means an expert in Solar thermal, so I apologize in advance if I am missing something in you plan or discription.

Thinking Outloud, wouldn't you want the solar to preheat the incoming cold water before it hits your masonry heater. Heres my logic please everyone correct where I am wrong.

If you use the solar thermal array to warm the coldest water, you will increase the amount of time the array can contribute some heat. I.e the array can warm 60 degree water to 70 degrees, when it cannot raise 90 to 100. Under this scheme even raising the masonary heater inlet temperature a few degree would mean that less BTUs are robbed from the thermal mass.

I am not sure if I am being clear; under what you described I am picturing a scenario where the incoming water sucks too much heat out of the thermal mass warming the water to the point where your solar thermal array can not contribute.

SolarLurker · January 2012

Re: Please critique domestic hot water plan

So I am think it would look like this;

Incoming water goes to solar thermal tank, heated by thermal array.
Preheated solar water passes thru masonry heater
Masonary heater water goes to back up on demand heater
Back up heater goes to end use.

You would need a bypass valve to circumvent the Masonary heater during summer months.

If you have sufficient thermal mass, there should be no need to pull heat out of the Masonary heater and store the heat in solar thermal tank.

mike95490 · January 2012

Re: Please critique domestic hot water plan

Masonry heater loop, is in free air, and only heats for the hour or so, that the fire is burning. Then 12 hours later, another fire may be lit. My hope is to thermosiphon heat a 100 gallon tank, on the floor above the heater, which may only heat the water up to about 70-90F after 2 firings per day. And if we used water, the tank would be cooled somewhat by incoming cold water. The preheated water, would feed the inlet of a rooftop solar heat-ex collector/storage on the roof, with about 40 gallons storage. The collectors, below the storage tank, are a closed loop glycol, and have a fresh water cool-down if stagnant in sun for too long. The solar heated water feeds the "tankless" and it has a smart, variable stage burner, to accommodate varied water flow rates, and inlet temps.
Summer, only thing changes, is no masonry heater, and more solar. No plumbing changes/switching foreseen. Domestic water flows through all but the glycol collector on the roof.

Updated sketch attached.

Attachment not found.

westbranch · January 2012

Re: Please critique domestic hot water plan

Mike, I don't see the closed Gycol loop ??

have you considered evacuated tubes? like these http://www.wsetech.com/WSE58ST.php

SolarLurker · January 2012

Re: Please critique domestic hot water plan

I think the water tank is going to steal the heat our of your masonry heater. I would think you want the Solar to heat the coldest water. Unless of course if that is your desire to use the water tank as a thermal store, if so a two tank solution might be best. Inlet ->Solar tank ->masonary heater->storage tank->on demand->end use.

lets say its sunny out and you rob the thermal mass to heat your domestic water tank, if your tank temperature is above that of your collector, you will reject usable BTU's.

BB. · January 2012

Re: Please critique domestic hot water plan

If you have snow in your area--Evacuated tube collectors may not do as well has flat plat. The evac tube are so well insulated, they will not shed snow very well.

Evac Tube many be better for installations that need very hot water:

Solar hot water

I worry that they are expensive and fragile.

-Bill

mike95490 · January 2012

Re: Please critique domestic hot water plan

Mike, I don't see the closed Gycol loop ??

It's the Rheem Solaraide - and for frost, using good insulation should keep the external fittings from frosting up at night, there is 40 gallons of semi-warm water there.

"Hartgard fluid is a non-toxic, food-grade liquid, which provides freeze protection for the closed loop heat transfer loop."

"The Rheem Thermosiphon systems operate on the passive thermosiphon principle a ‘closed loop’ to provide fail-safe freeze protection up to -30°F of the collector closed loop. The closed loop consists of the solar absorbers, a single wall heat exchanger around the outside of the storage tank, and plumbing attachments."

westbranch · January 2012

Re: Please critique domestic hot water plan

OK , got it, the closed loop is inside the tank attached to the panels...
I had to rethink this setup... I see that you are wanting to use the 40 gal. solar heater as a pre-heater for the DHW. From RHEEM's brochure, since they do not indicate the tanks R value, I am not so sure about how long that tank would stay warm especially overnight.

Since you want to try to run this system without a pump have you given thought to plumbing the SHW (solar hot water) into the 120 gal tank. Would probably have to be mounted at or below the level of the larger tank to thermo-syphon.
Not sure about your winter solar insolation rates so winter may not gain you much, but in summer there should be no need for wasting ANY SWH due to stagnation/overheating.
What are your avg winter low temps, what is the risk of a pipe freezing frost?

HTH

CDN_VT · January 2012

Re: Please critique domestic hot water plan

westbranch wrote: »

What are your avg winter low temps, what is the risk of a pipe freezing frost?
HTH

Westbranch / Williams Lake , I believe Mr Mike is in Los Angeles, CA , I know it rains pollution particulates , but Frost ? In LA ?
Google reports 27F was the coldest on record in 1922 , 31f in 1944. Must be a warming trend.

So in the winter months we heat the DHW with our "Air-Tight" fireplace stove . I have had 5 over the years from the 70's to today. My (late) neighbour has had his stove and water heating system since 1950's so his wife once told me. Just last year that system was removed and ??

Mine is all stainless steel tanks with copper lines that have 4 FOUR !! Pressure / temperature safety valves and there release & drain is piped outside ..This is a must , You are now getting into boiler operation. I have no water pump to Thermosiphon or convection flow.
In the winter time WE get 2 showers in AM and then a load of washing, or 1 shower , 3 washing loads , dishes , and always have enough that were washing in warm water. Here you get to know your system .. The heat in the summer time is set by the DHW heater @ 130F , once the Airtight fireplace stove is working (November- march-april) the hot water is just below boiling , and the shower taps are pointed towards the cold side , summer it's 75% towards the hot side.

After a sunday , like 2day , No showers , washing, so later on the pressure reliefs will be singing off , might need to start a wash.

My tank is in series with the fireplace internal heating coil and the cold enters from below and hot rises to the top of the tank that is also out to a temperature mixing valve. After that valve it now enters the normal DHW tank that is off for the winter.

Every pound of pressure added to the water increases the boiling point of water , so your ~ 50# system pressure can make a deadly bomb ..
Your wood burning fuel is not a way to control the water temp , and the water pipes MUST always be filled with water / liquid in any flame area, if you allow steam / knocking pipes ETC. Then you will have leaks & a nightmare ..I have seen this ,, & I run . Seamed copper pipes split , house is just a mess..Not mine , but DIY'ers ..

The last 3 stoves I bought,I made the insert coils , Because the power's / dictators or now, want you to pay for fuel..and have stopped many from selling stoves with the water coils. My first stove was a anthracite stove called a geezer that heated the hot water, not in North America , and was later adapted to burn coal gas in the 50's . I last fired it up in 80's on CNG just for grins.

It works well but as some who post here have said , slow it is , but steady.
think as air bubble try to get UP and out so you cause no hot air pockets that will cause problems .

VT

westbranch · January 2012

Re: Please critique domestic hot water plan

Hi VT, are you getting the snow yet? 6 inches we got, not forecast... -19 while plowing the stuff off the road with the quad.

Yes I know from Mikes ID that he lists LA as home, but he is in the process of building a new abode and it, from his posted pics, seems to be up in the hills somewhere, hence the Q.

A geezser?, you want to talk to my SWMBO'ed. she grew up in Glasgie and speaks fondly of that 'new fangled contraption!' and laments the switch to Calor gas.

CDN_VT · January 2012

Re: Please critique domestic hot water plan

Is that what this white stuff is.
Dusting only here . 3 years ago we had over 5 feet / 2 meters /12 hands

.. I use a honda tracked or Kubota power driven snow shovel/blower. I live rural so need to look after ourselves. The Island has one snowplow and our dictators require it so Starbucks is open for there morning coffee,down @ the stew-pot.

Yes I see Mr mike is @ the BBQ , probably doing up that special Springfield flounder

.
Either way , Mr mike should think about any Plastic and real heat.. I hate microwaving plastics, boiling my food grade plastics for wine / beer making is considered to be toxic , there only food grade below a set temperature . So there is another thing to really consider.

I do have air expansion / anti knockers inline on the washing machine lines , Dishwasher line and a spare set( large 1.5 " copper and 2 foot tall each line) at the very top of the second floor guest bathroom . That is also with the pressure pump accumulator , but distance and pressure waves are handled faster by have the stand pipes closer..

Just many things to consider .. Safety / health first, pluming sucks,and stains.

VT

mike95490 · January 2012

Re: Please critique domestic hot water plan

1) site is northern calif, 1500' 25F nightly, 15F record. So, I'd hope insulated pipes do the trick.

Rheem is selling the Solaraide as a water heater, so I'd hope it has a respectable R value.

All the hot water is going to be the hard (L I think) copper line, not plastic. After the mixer valve going into the LPG final heater, it could be PEX.

Our new washer has "fast action" valves, it really shakes the pipes, anti-hammer traps will be in the laundry, and maybe other places too.

Entire "boiler" will be domestic water, stainless in the Heater, and copper for the rest of the hot, at about 60 psi from a 1500 gal elevated tank.

I'd like to use the roof top solar to cycle through the large storage tank, but as you say, I'd have to get it below the tank, which is on the 2nd floor, no easy roof to mount it on. But that would be a great idea, maybe I can sell SWMBO on a solarm canopy or something....

Dave Angelini · January 2012

Re: Please critique domestic hot water plan

If you want to avoid going down the wrong path then you need to experiment and start small with an open loop and learn the basics. Very few people do this right from the start without a pro.

mike95490 · January 2012

Re: Please critique domestic hot water plan

Dave Sparks wrote: »

If you want to avoid going down the wrong path then you need to experiment and start small with an open loop and learn the basics. Very few people do this right from the start without a pro.

Exactly. That's what this thread is about. So far, I've altered the storage tank from plastic, to metal, made it larger, and I think I will install a PV powered circulation pump between the roof top panel, and the storage tank, I can't get the collector low enough to thermosiphon, but a PV panel works with my low power, low risk ideas. All "seem" like good ideas at this time

I need to locate some thermal sensors that I can wire up in the closet, to get readings from the various portions of the system, anyone have suggestions ?

solar_dave · January 2012

Re: Please critique domestic hot water plan

Mike if your looking for a controller here is what my system uses
http://shop.solardirect.com/product_info.php?products_id=151

westbranch · January 2012

Re: Please critique domestic hot water plan

How far is the closet from the furthest sensing point?
for real close points, one for each point: http://www.dealextreme.com/p/digital-compact-lcd-thermometer-with-outdoors-remote-sensor-15553

CDN_VT · January 2012

Re: Please critique domestic hot water plan

mike90045 wrote: »

Exactly. That's what this thread is about. So far, I've altered the storage tank from plastic, to metal, made it larger,

That was a major point I was making , the heat from my airtight fire into the storage tank is VERY hot, this is where plastic melts or will release toxins.
The "anti-hammer traps" are close because IF the Pressure / temperature safety valves work , they make the violent shutters , and YOU have no control at that point , It's all good and safe , but hammering lines are just before failure.
K, L ,M copper Is thin wall , thick wall , thick & malleable type .

My stove is supplied and received with Thick walled soft ACR type for Air conditioning type , 3 Feet of it as a flexible connection, When the stove is hot to cold , Never seen any movement , but I need expansion and contraction areas that have the correct pipe/tube.

Myself If the solar has it's own coolant/transfer fluid , I would use a heat exchange system, be able to always have water to flush the throne and have a system off line while the sun or fireplace came back online.
Filtration of all incoming water is also a must, we have filter steps from sand/10microns etc.
Settlement in heating tanks must be flushed also.. Just things to consider..

Not trying to pea on your porridge , just stuff I have learn't over my trials. If i knew about flushing out settlement of sediment from the bottom of the convex formed end storage tank , I wouldn't have lost my tank 4 years ago. 20 year old tank.(edit add: my flush valve was not on the total bottom, but up just 3"/5cm's from the convex end) & i flused the tank. Now my replacement is raised and the flush drain is from that bung.
The old 20 year tank has been cut and a new formed convex bottom has been pressure welded on and now stands on legs for the drain bung & piping .. Spare ..

Who-da-thunk

not me twenty years ago.. So it was one day down while plumbing repairs halted the ranch life NOW..

HTH's

VT

mike95490 · January 2012

Re: Please critique domestic hot water plan

yep, I'm a nut about flushing water heaters, and plan to do so in the future.
Potable water is filtered in a slow sand filter, and stored in a 1500 gal tank, with ozonator to keep it fresh. Tank is > 100 feet in elevation, giving about 60 psi at house site. I'll plan on having a "whole house" final filter on the inlet water, which will split for hot and cold.

How long are those Deal Extreme thermometer leads ? ever tried splicing the cable ?? I've got about 40' runs to do.

re: differential controller - would prefer just a solar PV and matching pump.

stephendv · January 2012

Re: Please critique domestic hot water plan

mike90045 wrote: »

re: differential controller - would prefer just a solar PV and matching pump.

Not ideal without a diff controller, e.g. early morning, the main tank is still warm from last nights wood burn but the water in the solar tank is cold; when the sun comes out the solar pv/pump will start cooling down the main tank with the cool solar water. If not a full blown difference controller, then perhaps just a simple thermostatic switch that prevents the pv pump from coming on if the water isn't at least X degrees.

CDN_VT · January 2012

Re: Please critique domestic hot water plan

I haven't needed to cut and lengthen one , but for a few bucks ? leads are 28" long.
I use one of these also here is the spec sheet on it.

I think this is what stephendv is hinting at also.

VT

Bheki · February 2012

Re: Please critique domestic hot water plan

mike90045 wrote: »

All,
In the winter, I've been told, each firing of the masonry heater, can be expected to transfer 30,000 BTU to the water loop. The heater can only be fired 2x a day, 12 hours apart. I calculated that 30K BTU into 85 gallons would be a 44F rise of the tank temperature, per firing. Right ?
Attachment not found.

Hi. I'm new to this forum. Full disclosure: I am a Creative Spirit. That means I'm good with my colors, shapes, words, and wild ideas but NOT technical stuff. I have been living off-grid for two years now. I do understand completely what our system consists of, basically how it works but mostly exactly what the capacity is and isn't. Our system includes two masonry heaters. One with what I call a water jacket or water loop (ss) that exits into and runs through insulated copper piping going into a 75 gallon boiler tank (with built in additional heat exchanger for future addition of solar hot water). The tank is all tricked out with thermostats and valves and zones for in floor heat for the bathroom, one for the front porch and one dump zone outside which the water has never been hot enough to go to any of these other zones. We're running the Grundfos Alpha circulating pump. Yes, on the firing of the masonry heaters every 12 hours. I was told that I could fire them a MAXIMUM of every eight hours. Last Winter was a cold and windy one so I did fire them every eight hours for one twenty-four cycle on a couple really bitter spells. (Contractor problems equal envelope/draft issues with the cabin.) I did NOT do this continuously for fear of over firing the heaters. The water temp in the boiler tank does NOT, repeat NOT go up 44 degrees with each firing. The hottest the water in the tank has been is 107 degrees. The only thing I use hot water for is 20 minutes worth of showering which drops the tank 20 to 30 degrees. I then need at least two fires (24 hours) to raise the tank temp 20 degrees. Not using any hot water, I loose a couple of degrees between fires depending on how cool the mechanical room gets due to the weather outside. Summertime, it's cold showers. Woo-hoo, baby! I highly, highly recommend a licensed boiler, otherwise you could be building a bomb in your house ultimately ending in a very bad hair day at the very least. You can check out more of my adventures in off-grid living at my blog.

Please critique domestic hot water plan

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