Buffer Tank to extend cycle times

MikeBos

Hi, I live in Mass on the NH border ~ 1 hr west of Boston. Would anyone be able to suggest a contractor versed in buffer tanks? My goal is less frequent but extended burn times. I feel the frequent 1 to 2 minute burns are detrimental. I have a Taco RMB-1 mixing valve for 1st floor infloor heat coupled w/ oversize Buderus 95k BTU/Hr boiler. Indirect hot water tank and a 2nd floor baseboard radiant.

leonz

Speaking as a homeowner with a poorly insulated home,

How old is your home? Have you had a heat loss study completed on your home??

When was the last time your boiler was serviced and tested for efficiency? Is your thermostat near a window with extended solar exposure?

It is a case of how simple or complicated a buffer tank system you want if at all and whether it is piped in series piped into the boiler sump or parallel to your existing boiler.

With a buffer tank piped into the boiler sump the cooler return water while still warm will reduce the amount of energy needed to reheat it and you leaved the majority of the existing plumbing intact.

A parallel plumbed buffer tank would require a circulator to balance the water temperature to create more thermal mass.

Buffer tanks are typically used for wood fired boilers to create and store thermal mass. Buffer tanks offer you thermal mass and thermal mass is like money in the bank.

Do you have room for a large buffer tank??

The New Horizons people have a 490 gallon fully insulated rectangular tank that would give you a large amount of thermal mass to use, the issues are your boiler and your home and how efficient they are.

Using oil or gas to create thermal mass will become expensive if the home is poorly insulated.

I have a coal stoker boiler and it heats my home with 52 gallons of water in the boiler steam chest and the 225 feet of fin tube baseboard which I hate as it has low thermal mass. I use Anthracite Rice Coal for fuel.

Wood pellet stoker boilers will consume 2 tons of pellets for every ton of coal burned in a coal stoker boiler.

Have a heat study done on your home and then decide if the needed improvements if any like new windows, doors, added insulation and weatherproofing may benefit you more because it helps seal the home versus installing a 490 gallon buffer tank for thermal mass.

Jamie Hall

An hour west of Boston sounds like maybe the Greenfield/Orange area? If so, there are two contractors I can recommend who are excellent. Just click on the highlighted names to contact them. One I know services your area is @Charlie from wmass . The other is @GW , though I'm not quite sure if he will go that far north.

A one to two minute cycle time is not right, even without a buffer tank and even with an oversize boiler. Something is amiss either with the plumbing or the controls.

Charlie from wmass

garrityplumbing@gmail.com feel free to send me a few photos of your system and what you have for heat emitters. Well versed in buffer tanks and their use.

MikeBos

I am in Pepperell MA. Not western or even central Mass. I really would like a experienced HVAC guy to come by and eval things. @Charlie from wmass you still in scope ?

Charlie from wmass

Last I looked I had round tires not square ones on the truck. In all seriousness if you don't need me there in the next half hour we can discuss the issue and work it out.

Charlie from wmass

Buffer tanks are used for high temperature heat sources connected to liw temperature distribution systems. They fell out of fashion when modulation became more proficient at lengthening run times and allowing high delta T between the heat source and the distributor system. There are other ways to get away from short cycling by use of boiler controls that limit cycles based on outdoor temperatures. What is your fuel?

hot_rod

a determining factor with mod cons is how the lowest turndown matches the smallest zone btu requirement. 20-30 gallon buffers for mid cons are a typical size

You need to do some number crunching

Both formulas here

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_17_NA_Thermal%20storage%20in%20hydronic%20systems.pdf

MikeBos

My fuel is oil and a Buderus 115/4 95k BTU/Hr. It has a HydroStat 3250-plus. The mixer is Taco RMB-1 w/ outdoor reset. 3 microzones for the infloor on the 1st floor. I've tied 2 together for the extra load. The low temp each have a thermostat on the 1st fl. High temp zones are 2 on for 2nd floor baseboard and the DHW. Heat loss for the house, I believe, is 45k BTUH. This is only running in September to keep 40G DHW up to temp. What would be an optimum burn time? 1 -2 minute burns during the winter are not unusual but when DHW and/or any high temp zone calls burns are longer. My boiler does not modulate, correct? I was voted down when I considered a propane system back in 2016. What would you consider my options? I see:

Ignore and run w/ it.

Add buffer tank. If I used a buffer tank would it be only for the low temp?

Seems the controls keep coming up as a possible solution. I've been asked 'why dont you have a Buderus Logamatic`.

http://imgur.com/a/BnkwF

Charlie from wmass

Why don't you use the control by Buderus? Dropping your boiler temperature and increasing the the temperature range for on and off are also options. I understand the logic that brought you to a buffer tank, I am just a subscriber of K.I.S.S. and find adding elements seldom increases efficiency. There are exceptions but you are not using solid fuel, and you have a boiler designed to work with lower return water temperatures than a North American pin style boiler. Local ignorance of control function and operations should not prevent the consumer from having properly operating systems. This ignorance is not a thing local to you but to North America as a whole.

EBEBRATT-Ed

I would like to get a burn time of 15-20 min minimum, especially with oil the less cold starts the better.

MikeBos

Thanks everyone. @Charlie from wmass The 'control by Buderus'? Are you referring to the Buderus Logamatic. Is that thing magic? I will read the user manual. This https://www.supplyhouse.com/product_files/R2107-User.pdf Yes KISS is how I like it also. Dread having to cut into existing. @EBEBRATT-Ed hitting 15+ would be great.

Charlie from wmass

It has feedback options. The manual will explain it's potential fully.

MikeBos

After a look at https://www.supplyhouse.com/product_files/R2107-User.pdf I'm not seeing much that makes me think it has an advantage over the HydroStat 3250-plus. It does have a module to control a Buderus mixing valve for radiant but I already have the RMB-1.

hot_rod

General consensus is 10 minute run time, ideally 20 minute off cycle. the low temperature microzones will be the challenge. Short cycles really drive down the boilers efficiency, into the 70% or lower sometimes.

It's the dewpoint of the fuel that can cause condensation in the chamber or flue. That varies a bit with burner adjustment. 130F is a number used often for oil fired. That boiler design may be able to handle lower temperatures, but the flue needs to run hot, above condensing temperature also. How is it vented now?

Use the control as much as possible, second option a hydraulic fix.

Or downsize the boiler.

Here is an example of the math to determine what a small load, short cycle can do to efficiency.

Your observed 1- 2 minute run times are not kind to you.

Screenshot 2024-09-06 at 2.39.49 PM.png

Charlie from wmass

@MikeBos for your reference Hot rod literally writes the book on these systems.

Dave Carpentier

We have 6 zones (1 per room) on the in-floor, all on their own tstats, with a CI oil boiler. The random small zone calls were doing the short boiler runs, so I tied the 3 short non-bedroom zones together, and that helped a fair amount.

Playing with the mixer temp might help ? but watch for max recommended temps on the flooring (I cap mine at 100f due to laminate flooring).

Buffer tanks arent cheap, but a 12gal or larger water heater (with the elements removed) is.

MikeBos

@Dave Carpentier Thanks. I have 2 of the 4 tied together for the same reason. My infloor area is ~1200sq total My radiant has a poor deltaT (only a couple Deg). I have SmartTrac and 3/8 plywood over and then 3/8 floating eng wood. The floating floor was a mistake as there is an inherent air gap. In my opinion that is the issue w/ the deltaT. @hot_rod What do you have in mind as a hydrolic fix? If I was to double or triple the amont of H2O in my systems would I 2x,3x my burns? Also, Is downsizing done by replacing the Reillo 40 f5? We had a guy in to confirm the oil nozzle was the smallest possible. Also that screenshot sums up my motivation to improve. It is vented into an existing chimney that has been converted w/ a stainless liner direct to the Buderus.

DCContrarian

Looking at the spec sheet on a Buderus 95K boiler (https://www.supplyhouse.com/Buderus-G115WS4-109000-BTU-Output-Cast-Iron-Oil-Boiler-Chimney-Vent )

It has a water capacity of 10.8 gallons. With an aquastat range of 20F, just heating the water in the boiler takes 20F*10.8*8.3= 1792 BTU. That would take 0.0188 hours at 95K/hour, or 68 seconds. So that would be the expected cycle time with no load and no flow. Presumably the manufacturer is OK with that, they could have made the capacity bigger if they weren't.

hot_rod

If the goal is to lengthen the on/ off cycling, many of the new mod con type boilers can do that with the control, anti cycling, ramp delay, firing derate for example.

I doubt you have any of those functions? The manual should tell you what the control can do. You could home make an anti cycling control with a time delay relay, but no heat output during the cycle off time, if that is an issue.

So the mechanical fix would be to add fluid volume. If you have actual run data, loads, etc, use the formula in that Idronics for fixed fired boilers.

I recently bought a new out of box 18 gallon electric HW tank on FB marketplace for 150 and it has side and top tapings, so easy to use as a buffer. Fittings like these can increase the connection size.

I've used the 1" element holes also, but use Loctite or LeakLoc to put the nipples in, glue them in, it's not a true 1" NPT port.

There were some gasketed adapters around to turn that element port into a better NPT connection.

Two pipe direct to load is the simple way to pipe a buffer. The tank is involved as needed. It charges fully as the loads drop and you pull from it on the next heat call until it drops below a useable temperature. The boiler on/ off is controlled by a setpoint control with a sensor on or in the tank. Ranco ETC, Honeywell, etc for example. I just slide the sensor up under the tank insulation against the metal tank. It reads just fine like this.

More $$ complicated control would allow the tank to run up to 180F, pull the all the loads via an outdoor reset control. It just extends the drawdown time a bit. That info is in Idronics 10 also.

This is a tank I had at my last place. Low temperature via a 3 way manual valve, it floated with the ODR temperature. A 4.5KW element in case the boiler failed I had 15,000 btu/hr.

Screenshot 2024-09-07 at 9.51.21 AM.png

Screenshot 2024-09-07 at 9.43.35 AM.png

Screenshot 2024-09-07 at 9.42.06 AM.png

MikeBos

Thanks everyone. After reading the docs on the RMB and HydroState 3250-plus I don't believe there is a 'fix' that could get me to 10min burns via the controls. I could imagine improvement. That said a quick calc using the formula provide in Idronics 17 using a complete guess at loadmin of 1000BTU/hr and a10 minute burn to have 40f change in tank temp I get a 47gal tank requirement Does anyone disagree completely w/ me still considering a buffer tank? If tank then what is required for additional controls and how will tank be plumbed? And 40gal DHW has a good burn already so would be best to keep the separate? Would the tank ONLY come into play w/ the low temp infloor? Ie not the DHW or the top floor high temp baseboard. NOTE: I may not remain in this house for more than another 10-15 years.

hot_rod

You mentioned that you tied two of the micro zones together. Any idea of the load on those zones? 1000 btu is a fairly low number. Something like a towel warmer by itself on a loop :)

One thermostat for all the radiant? but you have 12 actuators on the manifold?

Or is the high temperature baseboard the smallest, low load loop? How many feet of fin tube X 550 btu/ ft as a ballpark load estimate.

Calculate that low load number more accurately and play with the tank size.

That being said, 40 and 50 gallon electric water heater tanks are the most common, and usually less $$ than the 10, 18, 20 and 30 gallon size. If you plan on using an HW heater?

There really is no black/ white, yes no answer as to when to add a buffer tank.

For some people just hearing a boiler banging on and off multiple times an hour all winter is enough to make them add some volume to the system.

For you is the juice worth the squeeze? Would 15 years of this on your mind be enough to spend the $$. How much would you want to throw at the upgrade?

In your case, looks like space is tight so some re-piping would be involved depending on where you can locate a tank.

MikeBos

The 12 actuators?? Yea I don't. I imagine it could have been 4 but the manifold….. I don't know.

The on/off does make me cringe AND it is just below the 'TV room' so I hear it. I can imagine ~ $2k w/ whatever controls. ?????

Using 55 btu/hr I'd guess my 'office' loops add up to 200 ft. So 11,000 BTU/hr. Interesting that only bumped down the tank by 5Gal.

hot_rod

On the fin tube baseboard, 550 BTU per lineal foot. So 20" X 550' would be 11,000 BTU/hr on that zone.

So the short cycle isn't good for you or the boiler and components.

If you are a DIYer a tank, control and piping could be 2 grand or less. The tank being the big unknown.

An "official buffer tank,. TurboMax, Boiler Buddy, Lochinvar, etc alone would be over a grand.

For my systems I have made HW tanks work. They are glass lined 300 psi test tank, plenty adequate for temperature and pressure.

You can also get stubby tanks if space is an issue.

MikeBos

I'm getting in over my head. I'm still interested in a well versed pro in my area to design and install. Pepperell, MA. Thanks.