Zoning, Piping, and Panel Radiator Questions

Pulse

Piping plan: https://imgur.com/a/YmCSWOq

House floor plan: https://imgur.com/a/yCbw3w9

The pictures in the house floor plan include panel radiator sizes, calculated BTU load per room, ect.

I hope my heat loss calculations are good to go. I made my own excel spreadsheet. I even used a blower door test from 2013 to calculate air infiltration by volume and area. My home should have roughly a 33K BTU load. Certain things like the fireplace, upstairs hallway, hallway bath, and bathroom exhaust vents were not included.

I have my panel radiators sized for 120° SWT with a 63° Delta T. 70° indoor temp with a 7° design temp(99%). I do not know if using 120° SWT is the correct way to size them? I want max efficiency out of my condensing boiler. All of the rad sizes and locations are in the above picture.

My piping diagram shows 4 zones with homeruns. I am a bit concerned over short cycling since my boiler choices are either 85k, 110k, or 115k, with the minimum turn down being 8.5-11k. I am also tight on space with a 5'x4' mech room.

I plan to use 1/2" PEX for the homeruns to the panel rads, but what are the calculations to properly size my primary loops/manifolds?

Any thoughts/insight is very much appreciated!

Hot_water_fan

I do not know if using 120° SWT is the correct way to size them?

120 is not a "correct" or "incorrect" decision, more like a weighing of different parameters. 120 will work great. It means more panel radiators than using 140 but less than using 100. It should condense all the time.

I am a bit concerned over short cycling since my boiler choices are either 85k, 110k, or 115k, with the minimum turn down being 8.5-11k. I am also tight on space with a 5'x4' mech room.

Low heat loss + many zones + low design SWT can definitely lead to short cycling. On a 50 degree day, your SWT would probably be well <100, so not much Delta T to work with, and the minimum fire is probably > the max heat loss of any single zone. Only way to really do it is with a buffer tank. 30 gallons would get you there but space would be a concern. The boiler buddy tanks are tall and thin. One way around this is to use the buffer tank (in 2 pipe configuration) as the hydraulic separator.

Also, would you consider a single circulator for the zones? Using TRVs on each radiator, you could use a constant pressure pump and greatly reduce your pumping energy and save some space.

Pulse

Hot_water_fan said:

Low heat loss + many zones + low design SWT can definitely lead to short cycling. On a 50 degree day, your SWT would probably be well <100, so not much Delta T to work with, and the minimum fire is probably > the max heat loss of any single zone. Only way to really do it is with a buffer tank. 30 gallons would get you there but space would be a concern. The boiler buddy tanks are tall and thin. One way around this is to use the buffer tank (in 2 pipe configuration) as the hydraulic separator.

Also, would you consider a single circulator for the zones? Using TRVs on each radiator, you could use a constant pressure pump and greatly reduce your pumping energy and save some space.

What about switching to just two zones, first floor and second floor, and keep the TRVs on only the bedroom rads.

I like the stainless buffer tanks, IBC, Lochinvar, and HTP came out with. How do I calculate the BTUs a 25gal/30gal tank can hold? I could put the buffer tank in the garage, worst case.

mattmia2

Keep in mind buffer thanks are in the system water which is deairated, the steel buffer tank is no more likely to rust than the steel panel radiators.

Hot_water_fan

What about switching to just two zones, first floor and second floor, and keep the TRVs on only the bedroom rads.

Good option!

How do I calculate the BTUs a 25gal/30gal tank can hold?

BTUs = Delta T (Supply - return) x 8.34 (lbs/gallon) x gallons.
So a 30 gallon tank using a 10 degree delta t would store about 2500 Btus, allowing a 8k Btu minimum output boiler to run for about 20 minutes, not including the water in the rest of the zone.

Pulse

mattmia2 said:

Keep in mind buffer thanks are in the system water which is deairated, the steel buffer tank is no more likely to rust than the steel panel radiators.

Initially, I was trying to design a system with zero rusting components, but choose panel rads because I believe they are so much better than baseboards. ..based on your reply, I assume worrying about rust is irreverent with a properly deaerated/filtered setup? ..even decades later?

Hot_water_fan said:

BTUs = Delta T (Supply - return) x 8.34 (lbs/gallon) x gallons.
So a 30 gallon tank using a 10 degree delta t would store about 2500 Btus, allowing a 8k Btu minimum output boiler to run for about 20 minutes, not including the water in the rest of the zone.

Thank you, what is considered a good run time for these new condensing boilers?, ~20 min?

A turbomax indirect/buffer might be a good option for me.

mattmia2

There are hot water systems that are 70 or even 100 years old that used black iron pipe and cast iron radiators that are still in good condition. The most important part is to make sure it is leak free so fresh water with more oxygen is not added in to the system.

The only issue I can see to watch out for with the turbomax is that with your very low swt design you might need to run the system at a significantly higher temp to effectively make hot water. You would need to look at that carefully, I'm not saying it necessarily is the case but if it turns out you only need 95 degree water 4 months out of the year to cover the heating load that isn't going to be very effective at making domestic hot water.

Rich_49

Hot_water_fan said:

What about switching to just two zones, first floor and second floor, and keep the TRVs on only the bedroom rads.

Good option!

How do I calculate the BTUs a 25gal/30gal tank can hold?

BTUs = Delta T (Supply - return) x 8.34 (lbs/gallon) x gallons.
So a 30 gallon tank using a 10 degree delta t would store about 2500 Btus, allowing a 8k Btu minimum output boiler to run for about 20 minutes, not including the water in the rest of the zone.

Pulse

mattmia2 said:

The only issue I can see to watch out for with the turbomax is that with your very low swt design you might need to run the system at a significantly higher temp to effectively make hot water. You would need to look at that carefully, I'm not saying it necessarily is the case but if it turns out you only need 95 degree water 4 months out of the year to cover the heating load that isn't going to be very effective at making domestic hot water.

This is specific to the turbomax or any indirect? I thought the putting it on priority solved this?

-------

@Rich_49
Nice PDF, so..

If I have a 115K BTU boiler that modulates down to 14K(8:1) - 4K smallest zone = 10K left over BTUs x 20 minute cycles(10 min in the PDF seems low) = 200K / 10K = 20 gallon tank ..with a 30 gal buffer tank, I could have it run for 30 minutes

I am still trying to find out how long I should plan my boiler to run. I have no idea what the ideal run times are.

..but, either way it seems 4 zones for my house is a no go, maybe 2 max?

Hot_water_fan

@pulse with a large enough buffet tank (30 probably is enough for an 80k boiler with 10:1 turndown) you can have as many zones as you want. 20 minutes is a good start. The only quibble with the PDF is that your smallest zone may have a heat loss of 4K (if your calculation is 100% right) but that only occurs 1% of the time. That 1% of the time should find plenty of overlap with the other zones. What you’re really worried about is when that zones heat loss is 1k btu/h and your outdoor reset is sending it 85 degree water or whatever. 

Rich_49

HTP Pioneer , ODR I Series mixing valve , FPHX and flow switch for DHW , 2 circs .

https://www.htproducts.com/pioneer.html

OR

See page 19 of this document

https://htproducts.com/literature/lp-179_0921.pdf

Pulse

@Hot_water_fan
Exactly, my design delta T is 63°, if its 55° outside, that delta drops to 15°. That brings my entire BTU load down to ~11k with my smallest zone going to ~900 BTUs. Even then a 30 gal buffer should give me ~30 min run time with a 11k min BTU output boiler, even better with an 8.5k BTU min boiler.

@Rich_49
That Pioneer is pretty cool, but I dont think it is ideal for me. Looks like I can only get a firing time of about 15 minutes with that 55 gal buffer and 35k min BTU on a low demand day.

mattmia2

You can increase the delta t between cut in and cut out to lengthen cycles, as long as your return water temp is under maybe 110-120 you aren't going to get much increased efficiency so running a slightly higher cutout can give you longer cycles. this will also lengthen the off time so maybe you can get more like a 30 min on 30 min off.

The comment about the supply water temp is specifically about the turbomax which is a reverse indirect(or similar products). It is filled with boiler water and runs dhw through a coil to heat it so dhw priority won't help you, it will need to heat that whole tank of boiler water to get a higher outlet temp. If the system is sitting at 90 you won't get dhw over 90 until it heats the buffer tank over 90.

(you still might be able to hold it at say 120 and get decent condensing and mix the outlet of the turbomax system water down for the system)

Rich_49

Pulse . It actually is Ideal for you . Storing water at 160 -180 to make DHW and programming it to fire at 140* and using the ODR I Series mixing valve for heat exactly fits the bill .

mattmia2

except then he loses the efficiency gained from his larger emitters to run the system mostly in the condensing range if he is making 140 or 160 degree water.

Rich_49

mattmia2 said:

except then he loses the efficiency gained from his larger emitters to run the system mostly in the condensing range if he is making 140 or 160 degree water.

Maybe you missed the part about the Taco I series ODR mixing valve

mattmia2

Rich_49 said:

mattmia2 said:

except then he loses the efficiency gained from his larger emitters to run the system mostly in the condensing range if he is making 140 or 160 degree water.

Maybe you missed the part about the Taco I series ODR mixing valve

The boiler is still going to have to make higher temp water, the mixing valve won't help it stay in the condensing range.

mattmia2

Oh, the other thing you will encounter with your run time and buffer tank calculations is that the boiler won't fire at the lowest rate, it will try to meet the requested supply temp as quickly as possible so it will likely fire at a higher rate and run a shorter on cycle than the calculations suggest.

Rich_49

mattmia2 said:

Rich_49 said:

mattmia2 said:

except then he loses the efficiency gained from his larger emitters to run the system mostly in the condensing range if he is making 140 or 160 degree water.

Maybe you missed the part about the Taco I series ODR mixing valve

The boiler is still going to have to make higher temp water, the mixing valve won't help it stay in the condensing range.

Excuse me ? Geez , I must have been wrong all these years believing that RETURN or Entering water temp determined how much a boiler condenses . Please tell us more .

In regards to a buffer tank also , if one uses a 2 pipe buffer arrangement the buffer will see less flow and the boiler will always see the lowest water temps possible . If you store at high temp in that buffer and also use an ODR mixing valve on the system piping and program things properly the boiler will fire less often . Besides having low entering water temps and condensing , the most efficient boiler is the one that is idle / off .

mattmia2

Oh, i see you aren't pumping in/out of the tank with a boiler pump and using the buffer tank as a hydraulic separator, you are returning the water from the system through the boiler in to the buffer tank and heating it at that point. How do you keep the minimum flow of the boiler if doing that?

Rich_49

Download a copy of Idronics 17 . It's all in there , been doing it for years . The buffer is still a hydraulic separator

Pulse

I am confused how you use a mixing valve on the boiler supply side of things. I thought introducing new water into a closed system like this was something you never wanted to do?

Rich_49

The mixing valve does not introduce fresh water or any water for that matter . The Taco i Series ODR mixing valve simply has an outdoor sensor and opens and closes the valve mixing supply and return water until it achieves the desired SWT based on the outdoor temp .

https://www.tacocomfort.com/documents/FileLibrary/iSeries_R.pdf

Pulse

Im thinking ill drop down to "two zones", then use two Cross manifolds instead of TRV valves.

A 12 port manifold and a 4 port manifold for each zone. The 12 port manifold will have 11 panel rads on it, with a design day load of ~25k BTU and Delta T of 63.

Is the math below correct for the head loss of a single panel rad:

.067 GPM = 2100 BTU / 63 * 500 - for a single panel rad

0.05(120 water temp) * .71213(1/2" PEX) * 65'(Pipe length) = 2.314 * (.067(GPM)^1.75) = .02

So for my longest run the panel rad head loss would only be .02?

I am also not using any multipliers for the pipe length since they are home runs, no fittings.

Rich_49

Is the math below correct for the head loss of a single panel rad:

.067 GPM = 2100 BTU / 63 * 500 - for a single panel rad

0.05(120 water temp) * .71213(1/2" PEX) * 65'(Pipe length) = 2.314 * (.067(GPM)^1.75) = .02

So for my longest run the panel rad head loss would only be .02?

@Pulse I think you're using the wrong DeltaT and formula . Is the delta you're using the delta between supply water temp and room air temp ? It would appear that is the case . The Delta you want to use the formula you have is the Delta between SWT and RWT .

.21GPM / 20x500 is what I think you are looking for .


You realize using a Cross manifold you'll have to use thermostats and wire them correct ? They are zoning manifolds also so you'll be paying for features you'll not get the benefit of . You'd be better off using someone else's manifold and 2 zone valves , 1 on each manifold . Room by room zoning w/o the wiring will be all but gone

Pulse

I was probably using the wrong Delta, corrected

Calculation for 1 manifold with 11 panel rads: https://imgur.com/a/QY2JgaS

Headloss is only 1.26 and total GPM is only 2.6, seems low, but a 1" manifold and 1/2" pex will handle this no problem. Should I be calculating velocity/turbulence?

I know I will have a lot of thermostats, but right now with our **** electric baseboard there is already a thermostat in each room, so all the holes are there. I also wasn't liking having to go to each panel radiator and it seems turning off right at the manifold is a lot better than TRVs. What unused features are you referring to?

Hot_water_fan

1. Is the feet to panel roundtrip? If not, double those.
2. The head loss of parallel circuits is not actually summed, so your head loss is even lower.
3. Velocity is important: you can use a smaller tube and/or use a tighter delta T to increase velocity.

Pulse

I was only using the supply length, not return, so those all doubled. Either way my GPM and headloss is low all around, dont need very powerful circulators..

What is the equation for velocity?

EDIT:
61.75 density @ 120°
0.000375 viscosity @ 120°
0.485" ID of 1/2" PEX or .0404'

Flow Velocity = .295 = (.408/.485^2) * .17(GPM)

Reynolds Number = 1962 = (61.75 * 0.404 * .295) / 0.000375

My numbers are way low! I was using .17 GPM, which is my lowest panel rad flow rate.

How do I increase these rookie numbers, going to 3/8" pipe doesnt cut it. I would rather stay @ 1/2"