Seeking opinions on a boiler system redesign

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Old 03-18-13, 09:18 AM
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Seeking opinions on a boiler system redesign

I have a tri-level home build in 1956 with an original hot water heating system. The 2 upper levels use baseboard finned heating, and the basement has pipe embedded in the foundation. There are two thermostats, one for the basement and one for the upper levels. Both control solenoids to open or close circulation to these two separate water circuits. The original oil boiler heat source was replace in 2000 with a 82% efficient CGi gas boiler, 5 gallon, 130,000 BTU. The boiler is loud, inefficient, and has issues with the starting flame voltage rectification system that I have to fix from time to time.

I'm contemplating a complete redesign of the heat source and temp control, and am dreaming big. I want to solve a few issues I see with this system.

1. The boiler looks to be oversized; I've been measuring duty cycle during the winter months and think I can get away with 80,000-100,000 BTU.
2. Flow to the heating radiators is on or off, so the sudden influx of hot water causes constant tinging, pinging, and knocking as things expand and contract.
3. The boiler is inefficient and because of the placement in the home, the exhaust is pretty loud.

What I'd like to do is replace the boiler with a gas water heater. I would also like to replace the thermostat driven solenoids with a Labview controlled system that uses variable valves and an over damped PID loop so warm water is always flowing in equilibrium. The basic idea here is that instead of constantly cycling 160F water and then letting it cool to 70F until the thermostat kicks in again, a PID loop should be able to find a middle ground temperature based on outside temp and heat loss. If water is always flowing and only making small temp adjustments, I should eliminate the tinging and pinging of the heat cycles.

I have a friend who successfully runs a much simpler version of this type of system with two water heaters ,and a pump that always runs. He just adjusts the thermostats of the water heaters from time to time as the weather changes. He reports needing to keep the water temp around 85F for proper warming.

My system would operate differently. I would place a series of wireless thermocouples around the house and link them to Labview. Then, I'd write the PID program needed to directly control two variable valves for each of the two house circuits. With some testing and tweaking, I should get the feedback response I want. Instead of adjusting the water heater thermostats, I'd probably set them around 130F, and use the valves to control the percentage of hot water entering the system at any given time, versus recirculating.

Looking for advice or opinions on any part of this crazy plan. I believe I have the skills to make this happen, on the Labview side, and the hardware side. I will need to solder a new copper pipe configuration, as well as reconfigure the current expansion tank system.

Thoughts?
 
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Old 03-18-13, 09:39 AM
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1. The boiler looks to be oversized; I've been measuring duty cycle during the winter months and think I can get away with 80,000-100,000 BTU.
Do a heat loss calc on the home before you do anything.... There are stickys with links at the top of this forum.

2. Flow to the heating radiators is on or off, so the sudden influx of hot water causes constant tinging, pinging, and knocking as things expand and contract.
That is normal, although your boiler temps may be too hot.

3. The boiler is inefficient and because of the placement in the home, the exhaust is pretty loud.
How do you know its inefficient?


What I'd like to do is replace the boiler with a gas water heater.


Why in the world would you do that? They are really not designed for home heating and would really be inefficient....


I would also like to replace the thermostat driven solenoids with a Labview controlled system that uses variable valves and an over damped PID loop so warm water is always flowing in equilibrium. The basic idea here is that instead of constantly cycling 160F water and then letting it cool to 70F until the thermostat kicks in again, a PID loop should be able to find a middle ground temperature based on outside temp and heat loss. If water is always flowing and only making small temp adjustments, I should eliminate the tinging and pinging of the heat cycles.



Sounds like you want a modulating high eff 95+ boiler with outdoor reset... Thats essentially what they do.


Looking for advice or opinions on any part of this crazy plan. I believe I have the skills to make this happen, on the Labview side, and the hardware side. I will need to solder a new copper pipe configuration, as well as reconfigure the current expansion tank system.

Thoughts?
IMO your wasting your time. Sure you could do it but why in the world would you want to????

Did you run this plan past the spouse??????








 
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Old 03-18-13, 10:17 AM
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How do you know its inefficient?

Boiler is rated at 82% efficiency. Compared with modern boilers and water heaters, that is pretty low.

Why in the world would you do that? They are really not designed for home heating and would really be inefficient....

I know two people who have build homes around the use of water heaters and they work great. The nice thing about using these is how much energy you can store in 50 gallons of water compared with 5. Cycle times tend to be much longer because you have such a large heat reservoir, and using lower temperatures is generally more efficient.

Use a Water Heater to Make Radiant Heat Instead of a Boiler

IMO your wasting your time. Sure you could do it but why in the world would you want to????

Did you run this plan past the spouse??????


I'm willing to consider simpler options, or no change at all, but I do think some savings can be had and it would be a fun project. This is a DIY site right? The spouse trusts my opinion.
 
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Old 03-18-13, 10:45 AM
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Most standard boilers are the same eff at 82%... Water heaters have inefficient burners and a energy factor of only .62 or so..


Two 40 gallon water heaters would be 80k btu. Thats 80 k of inefficiency.


Here is a modcon that will probably heat your whole house. The burner modulates to the heat loss of the home. It will run at 11k - 55k... And is 95% eff.

http://www.lochinvar.com/_linefiles/WHN-02.pdf


but I do think some savings can be had and it would be a fun project.
Well have fun. Just trying to save you the grief.


This is a DIY site right?
Yep.... But you could install the proper equiptment yourself to. You are getting permits right? Curious to what the inspectors will say.




 
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Old 03-18-13, 12:52 PM
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What Mike is saying is that you want to reinvent the wheel... and that's fine if that's what you want to do. There's lots of things that I do that could be done more easily but I just do them because I want to.

Better keep a spare computer ready to run the system when that one crashes!

When / if you sell the place you will likely have trouble... new owners aren't going to have a clue what a PID loop is, or LabView, or any of that stuff, and you can be sure that the home inspector is going to ding you heavy for a 'real' heating system that won't require a college degree in programming to operate.

And yeah... the permits and inspections... that's gonna be problematic.

If it weren't for the fact that you just don't like the boiler I would suggest that you look into plumbing a BUFFER TANK, into the system, and use that as your 'battery'. Set up the boiler controls to maintain a setpoint temp in that tank. Use OUTDOOR feedback to run that tank as cool as possible, and then pipe the tank to your baseboards... constant circulation if you wish, and use indoor temp feedback to mix the circulating temp.

Google " BOILER BUDDY " and " iSERIES " valves.
 
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Old 03-18-13, 04:41 PM
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I would use ODR and constant circulation. The boiler only fires when needed and playing with the ODR you can get a perfect operation. No noises, lower fuel bills, even heating throughout the home.
Another option would be two stage hermits ate to use residuals heat first, providing your boiler is cold start.
 
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Old 03-19-13, 01:24 PM
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NJ:
The resale issue is a very good point, I hadn't even considered that. I don't plan on leaving anytime soon, but everyone thinks that before they need to move. The system I'm thinking of would be uselessly complicated for 99% of people. I was planning on having a spare computer, or a good override if things crashed.

rbeck:
What is ODR?
 
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Old 03-19-13, 04:00 PM
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ODR is Out Door Reset, a means where the circulating water temperature is lowered as outdoor air temperatures rise. Usually applied to the boiler and controls the temperature by the firing of the burner but sometimes is used with a three-way valve to only control the water circulating through the heat emitters. If you were to install the "boiler buddy" buffer tank I would strongly suggest the latter scheme.

I was a controls engineer in my former life and I also wanted to install a sophisticated temperature control in my house. The more I thought about it the less appealing it became. Experiments with micro-zoning some forty years ago taught me that you can easily spend far more on controls than you will ever receive in either comfort or economical payback. Even ignoring the complications that any new owner, or a significant other living with you might experience the capital costs vs. payback period usually makes these schemes nothing more than tinkering for the sake of just being able to do it.
 
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Old 03-19-13, 04:19 PM
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the capital costs vs. payback period usually makes these schemes nothing more than tinkering for the sake of just being able to do it
In my more energetic and foolish days, I designed, built, and installed a controller to limit my peak electrical demand by cycling my A/C. (We were on a residential demand rate.) Not a very good idea. I will be castigated here, but ODR, in my opinion, is a crock for many hot-water heating installations. The best boiler efficiency is achieved when the water temp is the lowest that avoids condensation. With a typical system with oversized radiation, best to leave the water temp alone at that temp, plus a reasonable margin. If there is excess radiation, jacking up the water temp in colder ambient temps is unnecessary, counter productive, and wastes fuel. In the remote event that the boiler itself in undersized, increasing the water temp will further reduce the net boiler heat output.
 

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Old 03-19-13, 05:26 PM
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I will be castigated here, but ODR, in my opinion, is a crock for many hot-water heating installations.
I'm not one that will castigate you... or even the other word that sounds vaguely similar!

I'm going to agree with you that ODR isn't a 'magic bullet' and may not in fact be appropriate for EVERY system.

For MANY it will help. For lots of others, not so much.

My home is very apparently over-radiated. In January this year we had about a week straight of design temps. The ODR was targeting a boiler max temp of 170 (which I had programmed it to).

While I don't have data logging equipment currently running, the numerous times I observed heat calls during that cold snap, only ONCE did the boiler temp hit 160 before the thermostat was satisfied.

HOWEVER... if one installed a CONDENSING boiler, and took the time to tune the reset curve to the actual heat loss of the home, and ran constant circulation in the system varying the heat output by WATER TEMP rather than BANG BANG ON/OFF, they could probably save some money. I'm SURE I could ... but I can't because no gas... but if I had gas, that's what I would do.
 
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Old 03-19-13, 05:53 PM
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I'm going to agree with you that ODR isn't a 'magic bullet' and may not in fact be appropriate for EVERY system.
Yeah, I wasn't thinking of condensing systems - for them, run the water temp as low as possible that will still heat the house, and ignore condensation concerns. With my natural gas for heating costing less than $1,000 per year (for a relatively large, 1950s house, 4 BR, 3 bath), it would be difficult to justify much capital outlay for ODR, etc., to save fuel, even if the savings were real. At church, I was consulted concerning an unsolicited proposition from the gas company to freeze their rates for a year, but of course the church would be on the hook even if gas rates dropped. My advice was, given the current glut of natural gas, forget it. Who was the gas company looking out for, do you suppose?
 
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Old 03-19-13, 06:21 PM
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Trooper, why not set your high limit at 160f and see what happens?
I am one that believes ODR is a good thing but one must take time to do the homework, heat losses, measure element, determine high and low water temps etc. the boiler efficiency is one thing but the largest fuel savings is system efficiency.
 
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Old 03-19-13, 06:31 PM
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the boiler efficiency is one thing but the largest fuel savings is system efficiency.
I think I know what boiler efficiency is, and how it is measured and calculated. How is "system efficiency" different and how is it quantified?
 
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Old 03-19-13, 06:34 PM
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Trooper, why not set your high limit at 160f and see what happens?
Not to hijack the thread, because I think DrJ can get good info out of the ODR discussion...

I plan to do that next year. I wanted to get a 'baseline' this year. I've got the smaller liner on hand ready to go in as soon as heating season is over and that will help with chimney condensation running at lower water temps and cooler flue gas. I'm planning on reviving the 'New MPO installation...' thread soon, with good info about how much oil it save me this winter! Keep an eye out in the coming weeks.
 
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Old 03-20-13, 10:54 AM
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It sounds like I may be better served considering a condensing boiler. I've also seen radiant systems run with on demand tank-less systems that seem to do well.

I like the principle of a continuous flow steady state system, but it seems like a big reservoir is needed to make that happen. I'm also not sure how to accomplish a variable flow (or temp) needed to make that happen unless the condensing boilers can minutely vary their temperature based on thermostat feedback.
 
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Old 03-21-13, 04:18 PM
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I like the principle of a continuous flow steady state system, but it seems like a big reservoir is needed to make that happen. I'm also not sure how to accomplish a variable flow (or temp) needed to make that happen unless the condensing boilers can minutely vary their temperature based on thermostat feedback.
With a STANDARD EFFICIENCY NON-CONDENSING boiler, yes, you would need a 'buffer tank' of some volume, because this type of boiler can not be run in the condensing mode without damage.

The tank in this case would feed a MIXING VALVE that would re-circulate a portion of the water returning from the radiation in order to maintain a setpoint temperature that was based on room temperature (INDOOR TEMPERATURE FEEDBACK)

A standard boiler would 'recharge' the buffer tank to a setpoint temperature not lower than it's condensing temperature, usually around 140. The tank temp COULD BE higher, up to 180, and the actual temp of the tank could be based on OUTDOOR temperature (ODR = OutDoor Reset)

With a CONDENSING BOILER (which are usually also MODULATING boilers, meaning that the actual heat output of the burners is being controlled by variable gas supply, the constraints about condensing don't exist.

A buffer tank won't be necessary when using a condensing boiler.

A condensing boiler is MORE efficient when operated in condensing mode, and it's built in controls will adjust the water temperature and heat output based on Outdoor, Indoor, or a combination of both, inputs.
 
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Old 03-21-13, 04:21 PM
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If you haven't already, check out the range of products offered by Tekmar Controls.

They've done most of your design for you already...

http://www.tekmarcontrols.com/

Read their essays and white papers...
 
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