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shashalou
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Posted: Sat Dec 8th, 2007 03:08 am |
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I'm completely at a loss in finding what I think I need in a water heater:
30,000 btu 30 gal
adjustable temp diff or minimal cycling 10 degrees
no electricity required for operation
possibly temp increase with outdoor temp
anybody have ideas?
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eleent
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Posted: Sat Dec 8th, 2007 07:08 pm |
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Hello: Not to be the bearer of bad news, but I don't think the attributes you're looking for exist in a single unit. Another way to deal with hot water is first to know what your need is and also, why you are looking for these specific criteria. There may be a different design that will meet your needs. So, let us know and perhaps with that info we can chip away at the problem 
Yours, Larry
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shashalou
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Posted: Sat Dec 8th, 2007 08:09 pm |
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We've talked briefly before, Larry. I use my tank for space heating, 30/30 is all that's required, no electricity is so I can use it during blackouts. The outdoor temperature sensor is purely for convenience (instead of manually adjusting the water temp). The most critical item is eliminating the 30 degree temp diff btwn on off cycles which raises hell with recovery in very cold weather.
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eleent
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Posted: Sun Dec 9th, 2007 12:27 am |
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Hello: Ok, some chipping away. Only an electrical control is likely to be able to get that ten degree differential. Another way to get the modern heater with a thirty degree differential to fire is to give it a small blast of cold water at the thermostat. This will make it fire up even though the bulk of the water isn't thirty degrees cooler. For example, it's a common complaint to have only slightly warm water first thing in the morning. It makes for short showers  . Opening a tap for a few seconds, fifteen or twenty minutes before showering, kicks on the heater and lets it get up to temp.
If there were a loop of piping hooked up to the heater, and this loop had a small pump in it, controlled by a timer, you could set the timer to cycle the pump periodically to force the heater to fire. Understand it wouldn't work in a power outtage, but would take care of the problem most of the time.
As this is for space heating, there likely is a loop already. (sorry I don't remember the details) Alternately, simply using a little hot water would put a slug of cold water to the thermostat, making it fire up.
For boilers there are outdoor reset controls. Boilers use AC power though. Depending on the length of power outtage, a battery and inverter, kept charged up and ready to go, could power modest loads. Although some boilers can modulate pretty low, 30,000 btus is a low starting point. If you could use a boiler, you could get that ten degree control with an electric thermostat.
How are you getting space heating out of the heater now, when power is out?
Yours, Larry
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shashalou
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Posted: Sun Dec 9th, 2007 04:46 am |
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Thanks for the interest. I understand there will be gives and takes. The question is which electric control is already fitted to a residential heater or which one can be retrofitted?
The heater only works by conduction during outages, I have a backup gas wall heater.
I use the cold blast in the morning to jump start the heater but I look for alternatives.
I dont understand your notion of a pump and timer since you need outside cold water to jumpstart. My pump runs continuously from Nov to Apr.
I could install a boiler and solve all the problems. Rather than getting involved in long dissertations, let's just say it's against my principles.
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eleent
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Posted: Sun Dec 9th, 2007 06:17 pm |
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Hello: More chipping... There is no thermostat I know of that can be used to control a standard gas heater, without replacing the existing control. I've looked for such a beast, with no luck. With the cold blast idea, I'm really talking about two different systems (although they both use the water heater as the heat source). One is the space heating system. which I imagined has a loop of water that cools down to ambient when it isn't running. The other was domestic hot water. If the heating pump were to shut off for a bit daily (instead of running continuously), on starting back up it cound provide that cold blast needed to kick the thermostat on.
I understand your reluctance to use a boiler. My place needs 27,000 btu at design load. I have a gravity driven radiant system, with a 40 gallon, 35,000 btu heater as backup. Wood is my backup of choice though. A boiler would likely be far more expensive and complex, aside from being about impossible to size for this load.
Not knowing the details of your system, understand I'm making some wild guesses about how it's put together. Whatever, there likely is a way to make it perform as you would like... Variable speed pumps are being introduced to the US market, and that may be another option to allow a greater delta T in the heating loop.
Yours, Larry
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shashalou
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Posted: Sun Dec 9th, 2007 07:24 pm |
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I dont mind replacing the existing valve, or the whole tank for that matter if I can eliminate that 30 deg differential.
My system is very basic, it is not closed, is fed directly from the hot side of the tank, a small pump in the return line goes directly to the cold side of the tank, 1" 10 ft copper manifold in and out, with four valved pex loops, the longest 150ft, with a switch on the wall to control the pump in the few instances that it gets too warm. Any plumber thats seen it says it cant work.
My problem is basically water temp and all I need is a steady 140 but I cant get it without setting the thermostat much higher than its designed for with some safety concern as well as economic loss.
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eleent
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Posted: Mon Dec 10th, 2007 12:53 am |
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Hello: One thought is that it may be possible to get what you're looking for by controlling that pump differently. It could be now that it is moving water through the tank quickly enough to mix it and prevent stratification. Do you know the difference in temperatures between water going to and coming back from the PEX loops? If a greater differential could be had, either by slowing down or throttling the pump, or by periodically shutting it down for ten or fifteen minutes, the control likely could be made to work as it is. I suppose a test would be simply to switch it by hand for a bit and see if that caused the heater to fire more regularly. Or, put the pump on thermostatic control, with the help of a relay or line voltage thermostat.
If you go to controlling the tank temperature thermostatically, the electric controls would be essentially what commercial heaters have, and aside from needing power, they are expensive.
One concern you may have heard is that there is a health risk in mixing potable water with heating water. When the heating system sits unused for long periods, there is a likelihood of bacteria growing in the stagnant lines. These get mixed with potable water when the system is turned back on when the weather cools. The usual fix is to put a heat exchanger between systems. Another approach is to not let it sit idle for any length of time. Even pumping it for a few minutes daily, throughout the year will make it difficult for bacteria to get a toehold.
Even though the plumbers are skeptical, clearly your system works. You probably have made the house very well insulated with very little air leakage. You may be giving the plumbers some ideas 
Yours, Larry
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shashalou
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Posted: Mon Dec 10th, 2007 01:19 am |
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A few quick answers, I'll be back to finish. I am aware of the bacteria concern. In the summer cold from the street passes first thru the loops to act as a basic air conditioner.
I have measured temp difference between source and return but memory fails now--I would guess its not more than 10 degrees.
My house is a barn remodeled in the 1930's. Ive got 7" cellulose in the ceilings and no more than 2 in the walls plus the 2" plank--not ideal conditions.
I have a 120 thermostat and tried it briefly--it never shut off.
Can you provide a link for commercial controls? Are they readily adaptable to residential heaters?
Thanks again for your interest.
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shashalou
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Posted: Mon Dec 10th, 2007 03:28 am |
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It could be now that it is moving water through the tank quickly enough to mix it and prevent stratification... If a greater differential could be had, either by slowing down or throttling the pump, or by periodically shutting it down for ten or fifteen minutes, the control likely could be made to work as it is.
I'm not sure I understand that. Would statification start the burner or prevent it from starting? Would fast moving water cause or prevent stratification?
Nor do I understand periodically offing the pump--the coolest the return water can be is room temp only 50 degrees or so less than the ave water temp and there's only a few gallons in the radiator. Seems tho washing your hands every hour would be as effective.
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eleent
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Posted: Mon Dec 10th, 2007 09:28 pm |
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Hello: It's good you're managing the bacterial risk... About temperature difference between in and out: it should be 20* or more. That low 10* differential suggests stratification in the tank is mostly gone. Stratification is good. If the pump is moving water too fast, water in the tank is mixed, eliminating stratification. Slowing the pump down and/or intermittant use will promote stratification and put cooler water back at the bottom of the heater, causing the thermostat to operate. If returning water was, say 80*, that still gives you 40* up to 120*; plenty to make the thermostat in the heater kick on. If the line voltage thermostat you tried didn't switch, try moving it to a spot on the floor, directly over a tube. There will be some sort of thermal lag to deal with when heating through the floor. Experimentation with thermostat location should give you a spot that works to control the pump and keep the house comfortable... All heater manufacturers use and have available commercial controls, but it's going to be around $1000 and not easily adapted to a residential tank.
The first thing I'd try is slowing/throttling down the pump to get a 30* differential, which is what you need to operate the thermostat in the tank.. Washing hands would probably work, but I'm not sure I'd want my hands that clean
Yours, Larry
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shashalou
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Posted: Mon Dec 10th, 2007 10:24 pm |
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one more please then I'll go try all this stuff. I have valves in all the loops would throttling them accemplish the same thing as slowing the pump?
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eleent
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Posted: Tue Dec 11th, 2007 01:45 am |
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Hello: Yes it would... but it would be better to use a valve on the outlet of the pump to accomplish the goal. There's a good chance of creating an imbalance in flow between loops if you use those valves to limit flow. The restriction should be on the pump's outlet to reduce the chance of cavitation. Ultimately, if it works, a smaller pump would be the best fix. There are pump curves and system curves. If they can be matched up, you get the best performance for pumping energy spent. I'm not conversant enough with the inner workings of the system curve to cogently explain it, but anything by John Siggenthaler on the topic would be good to have a look at
Yours, Larry
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shashalou
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Posted: Fri Dec 14th, 2007 03:23 am |
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No luck so far, Larry. I installed the 110 thermostat in the cellarway set it at the temp showing on a separate thermometer--no radical change in the operation of the pump.
I set the lever valve filling the radiator (suction side) at 3/4 and checked temperatures with a meat thermometer--no real change 10 degree ave. Cut it to 1/2 still no change.
Temperature in the house remained fairly stable during these changes.
2 pieces of info you dont have--the top 16" of the heater has a 6" blanket; the pump is a small grundfos probably 1/12 hp.
I'm going to buy another meat thermometer so I can tape them in place to get better readings. Meanwhile I am trying to make some correlation between burner start or stop, the temperature in the cellarway and the pump thermostat setting.
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eleent
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Posted: Fri Dec 14th, 2007 06:40 pm |
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Hello: Some Grundfos flanges/unions have a screwdriver slot in them, indicating they are isolation flanges. If yours has that, a screwdriver can be used to partly close a ball in the flange. The smaller Grundfos pump might be good to think about too. It would be a UP 15-18-SU or SF. That's about 1/20th horse power.
I suppose using the valves in the loops can work, but you would want to temperature balance things. That means fiddling with it for a while (days) till you get similar temperatures through all loops.
Some thermostats have an adjustable differential. Does yours? If so, it would be useful to know where it's set.
Keep tinkering and keep me posted. I'm sure things can be made better
Yours, Larry
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shashalou
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Posted: Sat Dec 15th, 2007 04:57 am |
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The outside temp dropped 15-20 deg today. Now at 15 deg the burner is off, pump on, the temp near the thermostat and in the house have remained the same all day, the temp feeding the heater is 120 return is 100. Last measure was about 15 deg diff.
My pump is the 1/20 hp groundfos you mentioned.
Burner just turned on as I write--5 min after measurement.
Please dont feel obliged to answer each of these. I will try to throttle the pump again tomorrow and report, now that I have thermometers affixed to the pipes.
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shashalou
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Posted: Tue Dec 18th, 2007 12:23 am |
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A couple days of readings show the temp in and out of the loop at 135 and 110 and the temp in the house steady btwn 63 and 65 while outdoors btwn 12 and 30. The heater is at its max setting but I can get more. The loop is throttled at about 1/3. The pump seems seems not to be a factor since it's on all the time. If I could determine which part of the heater cycle to have it on, I might make it work near the stack. Should I throttle the system further?
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eleent
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Posted: Tue Dec 18th, 2007 07:55 pm |
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Hello: I'm a little unclear on some terms, but would be tempted to throttle things a bit more, just to increase the differential. Before doing that, I'd mark the valves and temperature setting so you can quickly get back to it if needed. A 30 degree differential would be nice. I'm unclear if you have the heater firing continuously now, yes? If so, there is no need to play with things further, as you're getting everything out of it, it can produce. Anyway, sounds like progress
Yours, Larry
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shashalou
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Posted: Wed Dec 19th, 2007 01:18 am |
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I'm unclear if you have the heater firing continuously
Not even close-- but I'll se if I can get a better answer
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shashalou
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Posted: Sat Dec 22nd, 2007 03:23 am |
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| From the measurements I was able to take, it appears as tho the burner is running 2/3 of the time with outside temp 25-30 and inside 62-65. The lever valve going into the manifold (before the individual loops) is cut to 1/2; the return water is 100-110 and the feed is 125-138.
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