Buffer Tanks & Mod Con boilers

hr

should be fairly close to the output of the boiler attached to it. Sure you lose some efficiency every time you pass through a HX. I'd guess with the low return temperatures snowmelts provide it would run high 90's. So a 140K Munchkin times 965% = 134K or so to the snowmelt.

Basically I turned the indirect into a large surface area, high volume heat exchanger. Ideally the tank should last a good long time as both side operate at 12psi, give or take, and ne, one side glycolled. neither sees new water, both sides being closed loop.

I'm not sure how Weil would view their tank used this way, but with 30lb relief protection on both sides it has all the protection, and then some, that it would as a DHW exchanger.

The boiler is actually sized to the snowmelt load and it has a few floor warming zones for a basement kitchen rec room and the main level kitchen tile. The radiant load is probably under 50 K so the tank capacity provides a nice buffer volume.

hot rod

Wayco Wayne_2

What is the advantage

of using a buffer tank with a mod con boiler. I'm skulling through a design where I have a radiant floor (60000 btuh), a radiator loop (30,000), and a snow melt (45,000) all running off a mod con boiler rated 166,000 output. I've been playing with the HDS buffer tank simulator but it is hard to imagine things whith a changing boiler capacity. Does anyone have any experience or input? Thanks for any help. WW

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Paul Rohrs_5

Wayne

Edit: Lengthening the cycle times, or preventing short cycling is the short answer.

What is the minimum firing rate of your 166K mod/con? As long as your smallest load 30,000 btu's is larger than your minimum firing rate, I wouldn't think you need a buffer tank.


The HDS buffer tank simulator is awesome. I have a 210K BTU boiler that low fires at 42,000 input and 38,640 out. My smallest individual load is 17,000 in a SOG master suite. Here are the HDS representations with a 5 (minimum) and 50 gallon buffer tank. The cycle times speak for themselves. I would like to see a little more flexibility with the "burner on" and "burner off" temperatures in future releases.

Regards,

Paul

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Wayco Wayne_2

My boiler goes down

to 40,000 btuh. The load design are for when it's cold out though. We have a lot of mild temps in the Winter around here and seldom see design conditions. I'm leaning towards a buffer tank me thinks just as a hedge to keep the cycles longer. Thanks for your input. WW

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Paul Rohrs_5

Personal Preference I guess

Here is a HDS representing your 30,000 BTU load and a 40,000 BTU minimum output. Shown is a 20 gallon and a 50 gallon buffer.

I REALLY like long off cycles so I would probably opt for the 50 gallon, but I would love to hear others input.

I wish I had more solar experience to respond to your other thread on Solar and Geo.

Regards,

PR

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Wayco Wayne_2

Thanks Paul

I just got off the HDS playing with the buffer tank and the injection loop simulator. What fun. I should stop and get some work done some day. LOL. WW

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hr

one method I used

I connected a Munchkin to a Weil Plus 6o indirect tank. The boiler heated the tank side, and I pulled the snowmelt (glycol side) from the outer tank (smaller capacity)

This gave the boiler the larger tank capacity for buffer and heating zones, and the smaller capacity side of the "tank in tank" indirect for the snowmelt.

As the house had several forced air systems I actually put the snowmelt on priority! It was a small garage approch on a north side, fairly low load but critical for entry purposes.

hot rod

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Wayco Wayne_2

Interesting!

How would you predict your capacity for the snowmelt? I was going to just use a 50 gallon elc water hear tank as a buffer, in series with the heating returns and a flat plate HX to seperate the glycol from the boler loop. Using the indirect tank in tank would make it a dual function appliance and save space. WW

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