Correct Plumbing for multi-temp radiant heat?

flyingmeatball

Hello,

I asked a question a few weeks back about choosing circulators correctly for a radiant heat flooring (thread here).

I'm now on to the plumbing design and I have a few more questions

As little background, I settled using radiant floor heating on the first floor, and I'm going to use a heating coil through the Unico high velocity system to heat the second floor. This will also serve as a secondary heat source for the first floor.

My three loads look as follows:

Unico heating coil: 140F water, 10gpm flow, 14.6 ft max head
Floor Zone 1: 120F water, 4.2gpm, 9.6ft
Floor Zone 2: 120F water, 9.2gpm, 14.5ft

In total, I need ~110K BTU/h, ~60K from the two radiant heating zones and ~50K from the heating coil

Currently, I have an old water heater that I would like to use if possible for DHW. At a later date I would like to add an indirect water heater to the system.

Questions I have:

1) Does my design look reasonable? Are there any glaring issues I haven't noticed? Is it advisable to run the heating coil, which requires a higher temp, in series with the two radiant floor circuits as drawn? the floor circuits are in parallel to each other.
2) I'm in Illinois, where we have wide temperature swings. In the spring and fall it can oscillate between 40 and 60 over a day, which doesn't always work well with radiant heat. How can I best setup the heating coil and the floors to run together? The heating coil is the ONLY heat upstairs, but on the first floor I have both radiant and vents. Is there a good way to be able to switch which is the primary heat source? In the deep winter the floor should be primary, but in spring/fall it should probably be
3) Would it be a better design to combine the two pumps that go to the radiant floor zones into one, and do zone controlling with actuators? I can't imagine a scenario where I would have the heat totally off in one zone and not the other, only reason to have two different pumps is manifold placement/temp control for bedrooms vs common areas.
4) Does anyone have a good recommendation for a boiler to use? I've oscillated between tankless, Polaris water heater, combi boiler. I want to make sure I'll be able to expand later with a tanked unit, but also so that with just the three heating zones I won't be short cycling.

Plumbing layout attached.

Thanks!

newagedawn

the primary pump should be close to the air separator and you can use 1 pump for your radiant zones with zone valves, dont want to push the gpm to fast on those and a single pump can handle the gpm, happy piping

newagedawn

also,the unit heater piping configuration looks spot on, but want to pump into the 3 way valve for the radiant zone,
if i can recommend a great book for this application, it would be "primary- secondary pumping made easy" by dan holohan cant go wrong reading this again and again, it will truly help your install, good luck friend

GroundUp

Layout looks pretty good. I'm a proponent of the zone circs and would leave it that way myself. As for the heat source, please forget about a tankless. Go with whatever boiler your installer recommends and is knowledgeable about. Don't wanna end up with a piece of equipment that parts are unavailable for and nobody in the area will service

nicholas bonham-carter

Have you done a heatloss survey, using the SlantFin app or similar?
Is that 120 degree temperature ok for your flooring?—NBC

flyingmeatball

Thanks Everyone for the insights. I have updated the diagram (attached)

@newagedawn just so I understand when you say:

newagedawn said:

also,the unit heater piping configuration looks spot on, but want to pump into the 3 way valve for the radiant zone

If I pump directly into the radiant zone from the heating coil, wouldn't that mean the flow rate through the radiant zones couldn't be higher than through the coil? I can envision many times when I have the heating coil completely off, but want to feed the radiant zone. (IE - night time when my wife and I are downstairs and we don't mind if the upstairs zone gets cold). I fed the heating coil back into the primary circuit so that I could control the flow rates independently, but let me know if I've missed something here.

@nicholas bonham-carter I have done a couple of load calcs, and drew up all my radiant zones in LoopCAD. The 120 temp gets me very close to the theoretical flooring limit. In actuality, If it's that cold I'd probably dial the temp back slightly and use the heating coil as a secondary to the first floor - I have about 20K BTU/h excess capacity on it relative to what's needed to heat the second floor.

newagedawn

your new configuration looks better, the indirect will need to be before the fan coil as you want the highest temp water going to the highest temp draw first, and indirect water heaters need all that 180 degree water for make up, as stated before get dan holohans book on primary secondary pumping made easy , its a real eye opener to understand multiple secondary loops off a primary loop, your a quick learner, do you know the size of the pipes you will need for the primary secondary loops? happy piping

newagedawn

have you considered true multispeed pumps like the grundfoss alpha? they will work great on your radiant

Rich_49

newagedawn said:

also,the unit heater piping configuration looks spot on, but want to pump into the 3 way valve for the radiant zone,
if i can recommend a great book for this application, it would be "primary- secondary pumping made easy" by dan holohan cant go wrong reading this again and again, it will truly help your install, good luck friend

Don't quite understand what Newagedawn is saying here . That being said , your circ placement for the radiant and mixing valve is correct , you must locate the circ within the mixed loop and cannot pump into the mixer .

flyingmeatball

Thanks @newagedawn

Copper is going to be 1". I would love to read that book - as soon as I get all this figured out though I'm moving on to learn about low-voltage electrical (cable, smart home system). I won't actually be doing the install (fortunately!)

I didn't think indirect water heaters required input temps of 180F, I've been eyeing the Lochinvar Knight/Squire combination and didn't see anything about the input temps being so high If that's the case, I would imagine the indirect water heater return should also be before the heating coil.

I'll take a look at the multispeed pumps, although I had been focusing more on getting a boiler with 10-1 turndown, which I thought would allow me to use a fixed pump.

newagedawn

yes, the fixed pump would work for the primary loop, because its a fixed gpm and btu, but consider multi speed for secondary loops, especially the radiant, good luck

Ironman

Why are you showing a mixing valve on the fan coil? It's not necessary: just set the boiler's limit to the water temp needed to meet design temps and adjust the ODR accordingly.

Also, you don't need 10 gpm going to the fan coil; 5 gpm would be sufficient to get a 50k output at a 20* delta T. The 10gpm rating of the coil is what the manufacturer used to get the highest rated output from it.

Also, as mentioned, you want to go with an actual boiler, not a tankless, or a Polaris, or a combi. I'd recommend that you look at the HTP UFT Fire tube boiler and size it to match the actual heat loss of the house and NO more.

Rich_49

Ironman said:

Why are you showing a mixing valve on the fan coil? It's not necessary: just set the boiler's limit to the water temp needed to meet design temps and adjust the ODR accordingly.

Also, you don't need 10 gpm going to the fan coil; 5 gpm would be sufficient to get a 50k output at a 20* delta T. The 10gpm rating of the coil is what the manufacturer used to get the highest rated output from it.

Also, as mentioned, you want to go with an actual boiler, not a tankless, or a Polaris, or a combi. I'd recommend that you look at the HTP UFT Fire tube boiler and size it to match the actual heat loss of the house and NO more.

Unnico is very specific about the flow rate through their coils Bob . Can't fault a guy for using Manufacturer spec

Ironman

Rich said:

Ironman said:

Why are you showing a mixing valve on the fan coil? It's not necessary: just set the boiler's limit to the water temp needed to meet design temps and adjust the ODR accordingly.

Also, you don't need 10 gpm going to the fan coil; 5 gpm would be sufficient to get a 50k output at a 20* delta T. The 10gpm rating of the coil is what the manufacturer used to get the highest rated output from it.

Also, as mentioned, you want to go with an actual boiler, not a tankless, or a Polaris, or a combi. I'd recommend that you look at the HTP UFT Fire tube boiler and size it to match the actual heat loss of the house and NO more.

Unnico is very specific about the flow rate through their coils Bob . Can't fault a guy for using Manufacturer spec

I know Rich, but so are a lot of others if you want full output. I just wanted him to know that he didn't need that many gpm to get 50k btu.

flyingmeatball

Hi @Ironman - I put the mixing valve at the end of the heating coil circuit to divert away from the loop into the radiant floors in the event that the return from the heating coil was < than the required temp into the floors. I'm not sure that it's an event that will happen frequently, but that was my thinking. For example, if nobody is home upstairs and we're fine letting that zone go colder, the heating coil, which heats the 2nd floor, might only be taking in 120F water. Then out the other end would be ~110ish? If I DO want to heat the radiant floors on the first floor, they couldn't get an input of 120 if it called. Am I thinking about this wrong?

Thank you for the recommendation on the HTP boiler - I'll take a look at it, looks like a decent unit. I have been oscillating between a Lochinvar WHN156 and a Navien NHB-150. This seems like another good candidate.

Ironman

You need a boiler in the 120k btu input range - don't over-size.

The mixing valve is not gonna get you any more hot water to the floor, nor do I think it's necessary to do so. It also won't work the way it's drawn. Just pipe it p/s and regulate the flow rate to the coil with the correct speed selection on the pump.

SuperJ

If you decide to pump everything separately make sure you don't end up with 500watts of pump running all winter. It's not necessarily bad to pump each zone separately but often the most available (not most suitable) pump gets used and you end up overpumping, wasting electricity and killing system efficiency by lowered your delta. Don't forget your checkvalves if you have pumps in parallel. (you can often make up for a slightly undersized pump with a tiny bump in SWT, but it's really not feasible to overcome a low SWT with more pump.)

Personally I would put a single delta P pump on your infloor system, and put actuators on your manifolds.

The Unnico might be a good candidate for for a delta T pump since it won't need anywhere near 10gpm for 98% of the year I bet. You could set up the delta T pump to supply a constant air temperature too. I agree with others, you don't need the valve on the return from the Unnico.

Putting a OAT reset mixing valve on the infloor is a great idea, that way you can run basically constant circ for improved more even heating. The thermostat will just shut off the call for heat if things get too warm, but the valve can do the heavy lifting for temperature control.

For your primary pump you want to size for maximum reasonable delta T at high fire. Depending on where you place your system sensor the boiler will modulate to maintain a constant system temp even if primary flow < secondary flow. But, a nice plus for Lochinvar if you're a controls geek, is that they support a 0-10v signal to modulate the primary pump. Grundfos has some 0-10v capable variable speed (non-ecm though) small wet rotor pumps.

Have you considered a hydraulic separator? Just run all your secondary supplies/returns off a decent sized header on the secondary side, and place your boiler system sensor next to the secondary outlet port. Simplifies piping and gives you more functions in one device.




(image from this article: https://www.pmmag.com/articles/99599-out-of-touch )

flyingmeatball

Thanks @SuperJ and @Ironman

I will go with a ~120K boiler.

I have updated my layout (attached). The output from the unico coil now feeds directly back into the primary circuit. and I added a delta T circ there. I added a delta P circ to the radiant zones. I have check valves in place, but let me know if they are incorrectly placed.

I considered a hydraulic separator, but all of the literature/threads I could find on it seemed to point to it being unnecessary for this small of a load (apart from the fact that they're pricey. I'm not quite following what the advantage of that design would be over mine - I still end up with the same 4 circs (primary, unico, radiant, indirect tank). Maybe it's just me but that diagram is harder for me to follow .

Ironman

A hydraulic separator like the Caleffi Sep4 would take the place of the air separator, the need for closely spaced Tees, and provide dirt and particle removal.

I'm not sure where the load size becomes a determing factor, but I wouldn't consider 110k btus a small load.

flyingmeatball

@Ironman

So in that example how would I size the pumps? My loads look as follows:

Unico heating coil: 140F water, 10gpm flow, 14.6 ft max head
Floor Zones: 120F water, 13.4gpm, 14.5ft
indirect water heater: 140F water, ?gpm, ? head

The first two are easy enough to size, but I don't quite know how to do the indirect water heater or the primary pump.

Lets assume I go with Lochinvar KH-155 boiler and SIT-050 indirect.

Would my primary pump need to max out at the floor zone? Anything to the floor will first go through the heating coil at worst.

Ironman

Size them for the head loss through the boiler and the indirect coil. Nothing on the secondary side of the LLH.

The Loch I/O manual has head loss tables for the boiler.

SuperJ

Choose a pump from the table in the manual that matches you desired delta. You don't have to worry about the pressure drop of your zones for the primary because you've used closely spaced tees to decouple pressure. You can select a higher delta (25-30f) to ensure low return temps as long as you place the system sensor in the right spot. You don't want the hot supply being pumped straight into the return on mild days. A lot of people overpump their primary and get hot diluted return water temperatures.

I'd wager the grundfos 15 58 on speed 3 would work for your primary pump. See the attached manual screenshot. It has sizing details.


Indirect will probably be another 15-58 pump. It has 3 manually selectable speeds.

SuperJ

The popular grundfos alpha2 and the Taco VR1816 don't have the ability to move the required flow at the design pressure drop of both infloor zones simultaneously.

This one should work for you infloor if you want a single delta p pump (it does way more than delta p).
https://www.supplyhouse.com/Grundfos-98126819-MAGNA1-32-60-GF-Cast-Iron-Circulator-Pump-w-Speed-Drive-1-6-HP-115-230V
The magna pumps are awesome but $$$. You can hook up extra temp and pressure sensors to do all kinds of funky stuff.

Ironman

I think that I'd go with two Taco 007E or two Alphas and set them to the needed speed. The Magna would be over-kill for this job.

@flyingmeatball
How did you come up with 9.6' of head on one manifold and 14.5' on the other one? Those numbers seem off. What is the length of the longest loop on each manifold?

flyingmeatball

@superJ thanks for the recommendations - what about a circ to the indirect water heater? Would that need to be a 15-58 as well?

@Ironman the 007E has a max head loss of 10 ft - both of my zones are at or above that. The zone with the higher head loss has longer runs, averaging 230 ft, whereas the other zone is only 170 ft on average. The higher head loss zone is also going through some high heat loss areas - we have a sunroom that is 50% glass with unconditioned space on 5 sides. We also have a wall that is floor to ceiling glass. The actual numbers are coming from LoopCAD, where I entered all of the structural information and loop design.

Ironman

Are the loops 1/2" pex?

flyingmeatball

Yes - 1/2" PEX

Ironman

Something's off in your data. How many loops on the larger zone and what's their spacing O.C.?

.7gpm is about the maximum you can expect on a 1/2" loop. At that flow rate, the head loss is 4', not 14'.5'. You only use the head loss of the longest loop + the manifold and branch piping. You shouldn't be more than about 6' of head total. An Alpha or a 007e will pump that just fine.

I've got jobs with 2 or 3 manifolds and 14 - 16 loops of 1/2" pex, 250' length and ONE 15-58 is pumping all of it just fine.

flyingmeatball

Here is my PEX layout. There are 7 circuits on the manifold. Circuits B6, B9, B11 are what drive the high head loss. I believe those areas are 8" OC, but I'll have to check when I get home.

SuperJ

I agree with @Ironman based on your BTU requirements, it should be possible to pump your all your infloor with a single residential ECM circ pump (like the Alpha2).

But, infloor heating is not forgiving to underpumping. If possible, better to bring your fthd requirement down, than overcome it with a bigger pump. But if the design is fixed, than make sure you select your pump carefully by plotting your system design point (10gpm@14.5fthd) on the pump curve.

Lots of small pumps give you 10gpm or 14.5fthd BUT NOT AT THE SAME TIME. That's why looking at the curve is so important.

10gpm for 50k btu seems off. There should be a table to derate the Unnico coil with lower temps and lower flows. 10gpm would give you a 10F delta which is pretty low, is it a single pass coil? The 10GPM is probably to give you the max rated btu output which is likely way higher than 50kbtu if it needs 10gpm to get there.

Your layout is solid, I'm just trying to give you some feedback to maximize your systems potential. Don't think I'm being overly critical.

flyingmeatball

@SuperJ Totally appreciate the feedback! I'd rather you give it to me straight and I can adjust/learn than go ahead with a sub-optimal design.

I'm at a bit of a loss of how to modify the fthd - The only thing I cant think is that the software is not recognizing the wall between the garage and the mudroom as being solid, which means the heat loss in those rooms is super high, I will double check that when I get home. My only real choice for reworking the layout would be to shorten the loops, right? The problem I'm having in doing that is then I use most of my PEX getting back and forth to the high heat loss areas. The center of my living room/dining room will be hot, but I really want the windows to get most of the heat. If possible, I don't want to add manifolds if I can avoid it because it's going to boost the complexity/cost.

There is in fact a detailed table for the Unico coil - here. It's the HW3642 model. In theory I could hit the required load for the 2nd floor with 4GPM @ at a head loss of 2.6. However, I had in the back of my mind that I could use the the heat coil to heat the whole house in the spring and the fall when the loads aren't high. Because the radiant flooring will be high mass (1.5" concrete), it won't be good for those days where it gets down to 40, only to be back to 65 the next day. If I could keep flexibility with the Unico coil to hit the 10GPM/14.6 ft head, it would let me cover days where load might only be 70k, instead of the full ~110k design load. Does that make sense?

SuperJ

Consider designing for a slightly higher than 10F delta, will allow you to use water a bit hotter with less flow. Since you are doing a OA reset at the mix valve the hotter design temperature may not be an issue.

Another thought is, since you have the Unnico do you need to carry the whole heat loss on the floor? You could keep your floors warm and deal with design day heat loss with the Unnico.

With the Unnico coil, you'll notice the capacity goes up a lot with a boost in temperature, but changing the flow from 6-10gpm gives barely any extra capacity. So it looks like you could use the VT2218 on the coil. You'll end up with about 9gpm max which is sufficient.

Here is the coil pressure drop overlayed on the pump curve.

flyingmeatball

The den will no longer have radiant - top floor is now heated by Unico instead.

Also, I can't operate at 160 or 180F - I will have outlets close to the ground, but It looks like I can still probably use that pump and get most of what I want from the heating coil.

SuperJ

The 15_58 would be a safe bet for the water heater as well.

flyingmeatball

Thanks SuperJ - appreciate all the help!