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Need advice regarding adding buffer tank and replacing mixing valves

scott w.
scott w. Member Posts: 188
edited November 2022 in Radiant Heating
Have 4 zones at present that run of a W/M Ultra boiler. Zone 1 is for cast iron radiators, the other 3 zones are radiant heat in bathrooms, kitchen, and a large family room on a slab. Adding another zone for radiant heated floor in garage that is under the house.

At present some of the smaller zones are on and off quite a bit which seems inefficient. Would it make sense to add a buffer tank and change out the manual mixing valves to something a bit more sophisticated? Have a proposal for changing the mixing valves and adding buffer tank when adding the additional zone for the garage radiant heated floor.

What is the general thoughts on Vaughn buffer tanks? What are the parameters for sizing buffer tanks? What to think about when choosing a buffer tank?

Would the Taco mixing valves that are attached give better efficiency than the manual mixing valves that are currently installed.

Any advice would be appreciated. A professional would design and install all components.

Thanks

Comments

  • Ironman
    Ironman Member Posts: 7,076
    Smart mixing valves  with ODR are a much better choice for a slab and a properly sized buffer tank can prevent short cycling.

    Have you done any type of load calculation to determine if your boiler is sized right or if it has enough capacity for an additional zone?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 18,222
    Here is the formula for sizing a buffer on a modulating type boiler.

    Download this Idronics for info on reset controls.

    Either run the boiler on ODR, or run the tank hot and pull the load off the tank via ODR.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • scott w.
    scott w. Member Posts: 188
    edited November 2022
    Forgot to mention I do have ODR tied to the boiler. The boiler does have spare capacity. It is a W/M ultra 230 . Only adding about 6 or 7 thousand btu's to the load due to the removal of a vary large ceiling radiator in the garage. I think the rad is about 13 thousand btu's.
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,011
    edited November 2022
    Does the boiler turn on and off frequently or just the zones? I’m not convinced a buffer is needed with slabs and cast iron. How much fuel did you use last year? That’s a massive boiler. 
  • hot_rod
    hot_rod Member Posts: 18,222
    I think the Ultras are only 5:1 turn down. Is it a 230,000 input? Do you know the size of the smallest load? Is it common for only that load to be running? Very often?

    That is how you would "predict" how viable a buffer would be.

    Even with high mass distribution, if you had a single radiant zone, like a bathroom or any load under 10,000 btu/hr you run in to short cycle possibility.

    Depending on how sophisticated the data logging is on that model, it may tell you run times at various % of fire. Maybe % or hours at various turndown rates.
    That too could help make the decision.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • scott w.
    scott w. Member Posts: 188
    Unfortunately the W/M is an older model from 2008 or 9 and does not have some of the newer features. The reason the boiler is so large as the house built in 1928 is three stories built of exterior brick and inside walls are plaster over the clay tile behind the brick with 4,300 square feet and 36 windows (all now energy efficient), a few windows are quite large. House has 13 cast iron radiators and the piping for most of the second & third floor rad piping are in uninsulated chase's consisting of the exterior brick and clay tile. The boiler also heats the domestic hot water.

    I have insulated the heck out of the place where I could get access to several of the attics and knee walls. Even studded out a few exterior walls during renovation such as kitchen, den, living room and two bedrooms. All of the new windows and increased insulation and renovation plans were used in calculating the proper size of the boiler at the time of the boiler installation.

    Zone 1: Cast iron rads.

    Zone 2: gypcrete pour over slab with tile floor. This on slab zone runs the most. I did a gypcrete pour over on a slab as this bar/pool room was a later addition to the east side of the house in the 50's that also included a porch that that was made part of this space by a previous owner, Room is 36 feet long and had its own forced air furnace before the renovation. Just to many dollars to break out all the old concrete and insulate underneath. Included on this zone at the rear of the house is an enclosed porch/conservatory which is also on a concrete slab with a gypcrete pour over. Both slabs, I know, an energy drain and paying for it now with the high coat of gas. Thermostat is located in the large bar/pool/family room which also controls the other space, enclosed porch/conservatory. Porch/conservatory needs just enough heat to keep it in the 50 degree range.

    Zone 3: Gypecrete pour over joists (insulated) with tile floor The smallest of the four radiant zones has three bathrooms: master, guest and 1/2 half bath with one thermostat that is controlled from the master. I do not know what the load is for the three bathrooms. This zone runs alot does have a tendency to make the boiler short cycle.

    Zone 4: Kitchen and dinette, gypcrete pour over joists (insulated) with stone floor.

    Future Zone 5: Concrete garage floor ( insulated with two inch foam board) Pex designed and installed by professionals but not yet tied into the boiler. Another story......found the cast iron sewer line through the garage was all bad and could literally put a shovel through it. Only the dirt was holding it together. Have to have 75 feet of the cast iron pipe lined in the main basement. Cast iron was replaced to all baths from second floor to basement slab in renovation in 08/09.


    The three radiant zones are on and off quite a bit, sometimes within minutes of each other. Call for heat on zone 2 and when that zone has been satisfied zone three will come on a few minutes later. Same on and off with the radiant. I am thinking if the five radiant zones can pull off an appropriate sized buffer tank with some intelligent mixing valves including my current ODR could give me an boost in efficiency with energy costs and possibly help to extend the life of the boiler. Also included in the design is a ETC commercial temperature control by Ranco.


    Will this idea of using a buffer tank and ODR and intelligent mixing valves give me what I am looking for, a boost in energy efficiency and help lengthen the life of the boiler? Any thoughts on another design would be appreciated.

    Thanks

    Scott
  • scott w.
    scott w. Member Posts: 188
    edited November 2022
    Large boiler is due to a 4300 square feet Tudor three story home that was built in 1928. The construction of the exterior walls are brick with clay tile. Plaster over the clay tile on the interior. House has 36 windows, some quite large. I have insulated the heck out of the house with new windows & doors, studded out some exterior walls on the inside where I could such as the kitchen, den, living room and 2 bedrooms. Installed more insulation in the three attics and knee walls. Much of the piping to the cast iron rads are on the exterior walls that run to the second and third floors through exterior wall chases in the brick and clay tile and are uninsulated. The renovation including boiler and in floor heat was done during the 2008/2009 renovation of the complete house

    The W/M boiler was installed in the fall of 2004 so it does not have the updated tech of the newer models. The heating design in 2004 included all the new windows, doors, new insulation, on slab gypcrete pours and installation of the radiant heated floors in kitchen and baths when calculating the proper size of the boiler.

    I have four zones working at present and the boiler high fire has been set to 165 degrees. Zone 5 (garage) is not tied in to the boiler as yet until a decision is made un upgrading the mixing valves and installing a buffer tank. The work will be held off until the heating season ends.

    Zone 1: Fifteen cast iron rads and two in wall fin tubes, first floor: 6 rads and one in wall fin tube; second floor: 6 rads and one in wall fin tube; 3rd floor: three rads

    Zone 2: Bar/Pool/Family room was an addition constructed in the 1950's on the east side of the house. At that time former owner incorporated a 3 sided porch into this Bar/Family room addition by removing one side of the brick arches from the porch and makes the room 36 feet long on a concrete slab. Above this porch is the original master bath room. Porch had brick walls that had two large arches per side that were enclosed using studs and windows. New windows in the 04/05 reno now fill these arches on two sides This space before the 04/05 renovation had its own gas forced air furnace which I removed and did a gypcrete pour over with pex. Also included in this zone is a rear enclosed porch/conservatory also used gypcrete pour over on the rear porch slab. Both spaces are on one thermostat that is located in the Bar/Pool/Family Room. The Porch/Conservatory only needs enough heat to keep it in the 50 degree range in cold weather. Cost to pull up the old slabs and insulate was just to many dollars. This zone runs the most. I do realize these two spaces are probably the costliest to heat. I know, I have a nice snowmelt system on the exterior perimeter of this space. Both spaces have tile floors over the gypcrete

    Zone 3: Three bathrooms; master, and two guest baths on second floor. The thermostat is in the master that controls all three baths. This is the smallest zone and has a tendency to short cycle. All baths are a a gypcrete pour over joists and well insulated below the floor. All floors are covered in tile or stone.

    Zone 4: Kitchen & dinette, gypcrete pour over joists well insulated below floor. Stone covering gypcrete.

    Future zone 5: Garage floor, removed old concrete, two inch foamboard, pex installed per professional design with heat loss calculation for number of loops. New concrete pour. Not yet tied to the boiler. Am removing a massive radiator from the garage ceiling that is about 13,000 btu's. If I remember correctly the radiant heated floor load will be about 16 or 17 thousand btu's. The boiler has that extra capacity.

    Zones 3 and 4 seem to run off and on a great deal more so than the cast iron rads do. My thoughts are that an appropriate sized buffer tank and improved higher tech mixing valves (manual ones now and not sure if set properly) plus using my current ODR with the buffer tank will give me improved energy efficiency and help to prolong the life of the boiler. Utilizing the buffer tank should help to stop the on off cycle such as zone 2 fires and then is off and a few minutes later another zone fires and then goes off. Shouldn't the zones drawing off a buffer tank help to slow the number of times the boiler fires on and off in a twenty four four period? Seems the colder the weather the more the zones are on off within a few minutes of each other. I think colder weather makes some of the smaller zones short cycle much more often. Can't remember maybe it is the large zones on slab that short cycle in really cold weather.

    Also included in the proposal I have is a Ranco ETC Commercial Temperature Control. Not exactly sure how this piece of equipment will be utilized.

    Any other design ideas are greatly appreciated. Hope my description above can give some what of an idea of the layout.

    Thanks

    Scott
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,011
    edited November 2022
    Sounds like a great house Scott! 

    Just to clarify: you said “I think colder weather makes some of the smaller zones short cycle much more often.”

    Short cycling usually means the boiler turns on for a short amount of time. So the zones can open and close quickly but as long as one zone is open, the boiler should be okay - there will be a lot of overlapping demand with this much mass. A buffer tank cannot help the zones short cycling, which I understand to be what you’re describing. It will help with the boiler short cycling of course. 

    Do you have any sense of how many boiler cycles you average? And how much gas do you typically use per year?

    I’m leaning towards installing the next zone, then when the boiler is replaced (given it’s ~14 y/o) either get one sized correctly (assuming it’s oversized) and/or get one with a higher turn down ratio. The buffer tank is helpful, but you can improve without it in my opinion. 
  • hot_rod
    hot_rod Member Posts: 18,222
    I don't see this system benefiting much from add a buffer tank. Sounds like you have a lot of mass and fluid volume already.

    One option for the lower radiant temperature requirements is a manual 3 way mix valve. As the ODR changes the boiler SWT, that mix valve tracks along with it. Unless you know and can measure the exact SWT for the radiant it will be a bit of trial and error adjusting.

    Look at all the adjustment parameters available on that boiler in addition to ORD there are other functions to help lessen the on/ off short cycles.

    You will be hearing this a lot, the home and distribution drives the operating condition of the boiler. That much poorly insulated home will be an $$ heat.

    Balance comfort against efficiency. The most efficient operating condition of the boiler is when it is turned off. That may not be a popular option for you and the family?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • scott w.
    scott w. Member Posts: 188
    I may have caused a bit of confusion in the last post with my phrasing about short cycling and zone cycling. I do have short cycling where the boiler is on and off several times while calling for heat in a zone with the pump running until the room thermostat has been satisfied. Checked on the boiler this evening as it is getting colder and noticed boiler is doing that several times till the room thermostat has been satisfied. Shouldn't a buffer tank solve that issue? Thought that is what I have read in past posts here on The Wall regarding a buffer tank?

    Sorry I don't know all the abbreviations. I am trying to learn the lingo. What is SWT short for for?

    Thought the buffer tank could help also with the on off of the boiler when zones have call for heat at very close intervals by pulling heat out of the buffer tank that would help minimize starts and stops with the boiler......how is the buffer tank supposed to function? Does the boiler fire up to heat the buffer tank as soon as there is a call for heat and a zone pump kicks on? Isn't there a thermostat in the tank telling the boiler to kick on only when the internal temp of the tank drops below a set point? During real cold periods in the low twenties a zone will shut off and within a minute or two and another zone will kick on. That happens quite a bit.

    Not having the proper education in the subject is a bit frustrating for me. Wish I had a great deal more of an understanding of hydronics.

    Have the manual for the boiler but do not remember seeing anything about adjustments to the boiler. Hot Rod, can you point me to a source that I can learn a bit more about my boiler functionality if it has the capability? Could my boiler be of a vintage (2004) that may not have any adjustments? Assuming you mean internal adjustments to the W/M ultra.

    Mixing valves on each radiant zone are manual . Not sure if they are at the proper setting. Have tried to learn as much as I can from reading The Wall on the subject. Have seen posts from some of the knowledge people that say the water temp for pex should not operate above 110 degrees.

    Hot Water Fan, I don't know how many boiler cycles I average. How would I be able to find that info? I don't think the boiler itself is that sophisticated due to it's age. I think later models would give that info. Just looked at my paper records on usage and found the boiler was installed in the fall of October 2004. The big renovation was about at the same time. Time flies and memory gets kinda fuzzy. Thought reno was 08/09. Will have to revise earlier posts on age of the boiler. As far as usage, the CCF's from Jan. to Dec. starting full calendar year 2005 through 2021 range from a low of 1600 CCF in 2012 to a high of 1904 CCF in 2019 during a 16 year time frame. House is located near Pittsburgh Pa. The lowest dollar amount for twelve months was of course 2012 and the highest dollar amount for 12 months was in 2021.

    If I have a boiler failure and the current boiler needs to be replace I would install two boilers to fit the load. Looked at this several years ago. One to run during the shoulder season and then the second would kick on only when needed during very cold periods. I think that would most likely give me the most efficiency. Of course unless there are better boilers now available.

    I hope I am not beating a dead horse here.
  • scott w.
    scott w. Member Posts: 188
    edited November 2022
    After looking at my records I had to go back to revise the age of the boiler and the renovation project which was also done during the 2004/2005 period. Boiler was installed in Oct of 2004 so guessing the boiler does not have any ability to adjust it in any way and does not have a way of checking boiler cycle averages due to the age. later models were built with more sophisticated technology.

    Hot Rod my writing of the last post may have not been as clear as it could have been. Do have short cycling. Checked on the boiler tonight and found boiler doing several on off on off during a zone call for heat while the pump continued to run until the thermostat was satisfied. Buffer tank should stop this from happening???

    I do have manual mixing valves on the radiant heat zones. I am not sure they are set properly. I have read some posts on The Wall from what I can tell are from some of the more knowledgeable posters that pex should not have more than 110 degree water through it. That is how I set the manual mixing valves. Would that be correct? Is there some other formula for setting mixing valves.

    What is the abbreviation SWT ? I may have known this but have since forgotten

    Shouldn't a buffer tank also help with less boiler cycles when a couple of zones go off and on within short intervals (minutes) of each other ???? With a buffer tank I thought a zone or zones would draw hot water from the tank and the boiler would not fire until enough hot water would be withdrawn and the temp of the tank would go below a set point. I assume the boiler should not fire the instant a zone comes on and starts to pump hot water out of the tank?

    A bit frustrating for me not having a better understanding of hydronic design......wish I knew more. Reading The Wall has been very helpful over the years.

    Hot Water Fan, my lowest consumption of gas was 1500 ccf for the calendar year Jan. thru Dec. of 2012.
    I think that was a warm winter for near Pittsburgh, Pa. My highest consumption was calendar year 2019 which was 1904 CCF's. My records are for a 16 year period from 2005 through 2021. In dollars of course the lowest cost was 2012 and the highest cost
    was 2021 even though consumption was less than 2019. Have attached a photo of the pile of bricks.
    Hot_water_fan
  • hot_rod
    hot_rod Member Posts: 18,222
    One common length of time is 10 minutes or more of run time when a boiler fires up, and maybe a 20 minute run cycle after it fires. See how yours matches those numbers. The shortest cycles will be with the one smallest load zone calling. Has it run since 2005 without any repairs? Short cycling often takes out the fan motor, gas valve, igniters, or other components in the gas train of the boiler.

    I think that boiler came with several manuals, one dedicated to the control setup options. Do you have the manuals still? If not they are at the Weil website. It could be a function like anti cycling, that prevents the boiler from firing until a set time interval. But you need to make sure you still get adequate heat when you enable functions like that.

    Adding a buffer could be $$ and may not solve any issues or even reduce the heating cost. Normally the are used for RE systems like solar, or geo systems. On hydronics they can help if the boiler is way oversized, and the home has a lot of small loads, like maybe just a bathroom zone, or a single room zone.

    So, two way to see if a buffer would help. Sit and watch the boiler operate on low load days or single zone heat calls. Or do a lot of number crunching, a room by room heatload calculation as a start.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    scott w.
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,011
    edited November 2022
    Shouldn't a buffer tank solve that issue? Thought that is what I have read in past posts here on The Wall regarding a buffer tank? 
    Correct, in this situation a buffer tank would help with cycling. The tank temperature could be what controls the boiler, so you understand the operation well. It’s just…you add a buffer tank to a 18 year old boiler that uses between 1600-1900 CcF per year, maybe you save a couple of %? $20? $40?

    Back to the usage: awesome record keeping! The larger issue, which will be fixed when you replace the boiler next, is that your are extremely oversized. I’ll double check this, but Pittsburgh is around 5000 annual heating degree days, so you’re using about 1900*103kbtu*.95 efficiency/5000HDD = 37,000btus/HDD. If a day averages 5 degrees out, that’s 60HDD using a base temp of 65. So on that day, you’re using 60*37,000 = 2.2MMBtu. Divided by 24 hours, you get 93,000 btu heat loss. When the time comes, install a smaller boiler! You could get a 125kbtu or even 150kbtu with a 10:1 turndown, and with the proper settings deal with short cycling that way. As it stands, your lowest modulation level is about half your heat loss on the coldest day. Going from a low end of 46kbtu to 12-15kbtu will triple or quadruple the length of the shortest cycles. Add in a ramp delay setting and you're likely to have overlapping calls. 

    I wonder if a thread of the houses of the wall has been compiled. Yours is towards the top!
    scott w.
  • hot_rod
    hot_rod Member Posts: 18,222
    edited November 2022
    A pic of you piping may help. That boiler needs to be piped primary secondary. Improper piping could lead to short cycling if the boiler cannot move the heat into the system.

    I looked at the series 3 manual, there are some adjustments avail that may help. Do you know what series you have? You can adjust the modulation intervals, and a boost function could help with a conservative ODR reset curve.

    A good understanding of the system and what adjustments would effect would be needed. It would take some trial and error to assure any control adjustments were helping correct the undesirable condition.

    I believe that boiler turns down to 46,000, so it should not be oversized on a home that size, if the control allows it to be adjusted to the smaller loads.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • scott w.
    scott w. Member Posts: 188
    edited November 2022
    I looked at the paperwork on the boiler and it is a series 2 and is piped primary secondary Watched the on off today and boiler shuts down 3 or 4 times during a call for heat when boiler water reaches 165 degrees. Shut down lasts about 2 to three minutes. Then fires up again. Will get picture of the piping tonight.

    Hot Water Fan, I am kind of a bit anal when it comes to tracking gas and electric usage. It can be a way to tell if something is terribly wrong. At least I can use the data to see if there is some kind of trend. Have some of the prior owners usage and the winter bills were huge when the cast iron boiler was in use.

    The firm that installed the boiler, radiant floors and piping mentioned today about reviewing the heat loss calculation they did back in 2004 if and when I need a new boiler. The guy who designed the system in 2004 said the 150K W/M boiler was to small for the load and and the next size up was the ultra 230.

    I try to keep the thermostat in the high sixties during winter....Think a cooler house is healthier. Thanks for the nice compliment on the house.
  • hot_rod
    hot_rod Member Posts: 18,222
    It would be nice to find an installer, dealer or local factory rep that really knows that control. I suspect there is just enough function in that early version to "tune out" some of the cycle issues that you are concerned with. Lower the target temperature, let the boost take over if the heat call last too long, might be an option.

    https://www.weil-mclain.com/sites/default/files/field-file/ultra-series-2-control-supplement_1.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    scott w.