panel radiator sizing and design considerations

bmwpowere36m3

So I'm looking thru at various steel panel radiators and trying to figure sizing, SWT and placement. I found an interesting excerpt in the Buderus design guide which mentions:

Once a room exceeds 12 x 12', it is advisable to install 2 smaller radiators on the outside walls for more comfort

@SWEI‌
@Gordy
@Rich
@hot rod

Have you guys done this, i.e. install more than one radiator in a room? I have no problem sizing a single radiator that'll fit under a window in each room and supply the recommended BTUs. However what is your take on using more than 1 radiator.

GW

Seems a bit much, 12 x 12 is not very big, if you're talking normal rooms (not excessive glass, not excessive heat losses), I'd put one in double that room size. If you're talking old and clunky thermal envelopes yes load em up.

Do you think the old timers had wood stoves every 144 Sq ft? Maybe a silly example but still, it's all about how comfortable you wish to be.

Just my simple thoughts

Gary

bmwpowere36m3

GW said:

Seems a bit much, 12 x 12 is not very big, if you're talking normal rooms (not excessive glass, not excessive heat losses), I'd put one in double that room size. If you're talking old and clunky thermal envelopes yes load em up.



Do you think the old timers had wood stoves every 144 Sq ft? Maybe a silly example but still, it's all about how comfortable you wish to be.



Just my simple thoughts



Gary

Just something I read and thought I'd ask….

I thought maybe something to do with distance and amount of radiative heat.

Ironman

It's kinda like using two registers with forced air, instead of one big one. It distributes the heat around more evenly. You know, like "spreading the wealth around".

bmwpowere36m3

Ironman said:

It's kinda like using two registers with forced air, instead of one big one. It distributes the heat around more evenly. You know, like "spreading the wealth around".

I understand the premise… that's what I thought they were alluding to. However in practice, do a lot of guys install multiple radiators, when 1 can suffice and is not too big.

bmwpowere36m3

Different radiators have different plumbing options… what do you guys use to cover the piping coming thru the wall or floor.

All my pipes have to come thru the floor.

I figure the only options are either PEX or copper. I can run PEX or copper from the manifold. Or I can run PEX, but transition to copper right below the floor/radiator (so only the copper pipe is visible in the living space).

What's a good way to hide either the copper or pex pipe? Some sort of chrome tube (like a hollow tube/cover) and escutcheon would be great.

@‌ SWEI

I know you like the Myson Select radiators for price/value… Is there any benefit to having the TRV at the top of the radiator? If so, how do you best hide that pipe?

Most other panel radiators have a center/bottom connection, with the option of a TRV at the top. This way only 4-5" of pipe would be exposed (coming thru floor). Whereas with the Myson Select, if you mount the TRV at the top, you end up with 20+ inches of exposed piping to the TRV/fitting.

psb75

"Only options are pex and copper." (esp. if that includes: 1/2" copp., 3/8" and 1/2" pex AND Watts PERT). That leaves quite a lot of options. Esp. if you can also cover copper with chrome. Myson is the best value. They offer MANY different rad. sizes and styles of hook-up. The basic, Myson Select rads. each have three poss. piping configs--bottom to bottom, high right, or high left. Put the TRV on the supply-side. How far do you want to bend over to adjust? Myson T-6 Series has two low connections to the bottom center of the rad. Easy to pipe to. Pricey. If you want the pleasure of radiant panel heat and piping is underfloor, sometimes you have to be willing to look at plumbing! Sometimes the resulting comfort of panels makes customers' "vision adjust." This winter I installed 35 Mysons in three diff. houses. All working stellar.

hot_rod

If the room requires that much, split up the radiators so they are close to the "load"areas. If possible under windows works well as it blankets then glass with warm air flow.

Depending on the size you may put two in series with one TRV controlling the pair. Use an H valve with adjustable bypass, for series piping.

bmwpowere36m3

hot rod said:

If the room requires that much, split up the radiators so they are close to the "load"areas. If possible under windows works well as it blankets then glass with warm air flow.

Depending on the size you may put two in series with one TRV controlling the pair. Use an H valve with adjustable bypass, for series piping.

What do you consider "that much"?

Based on the load, I have no problem finding single radiators, approx. 24" tall that fit (width-wise) under a window in each room. For example my room to room loads are:

M.Bed: 4900 (6' casement window)
Bedroom: 5400 (7' casement window)
Living Room: 6900 (9' bow window)

hot_rod

I prefer the "look" of multiple radiators under the windows for example. If the room furnishings allow, outside walls and under windows is a good location.

I also like matching the width of the radiator to the window width if possible. That allows for furnishings to use the wall space and puts the heat output in the ideal location.

It's really what you like, as long as you cover the loads under design conditions.

bmwpowere36m3

psb75 said:

"Only options are pex and copper." (esp. if that includes: 1/2" copp., 3/8" and 1/2" pex AND Watts PERT). That leaves quite a lot of options. Esp. if you can also cover copper with chrome. Myson is the best value. They offer MANY different rad. sizes and styles of hook-up. The basic, Myson Select rads. each have three poss. piping configs--bottom to bottom, high right, or high left. Put the TRV on the supply-side. How far do you want to bend over to adjust? Myson T-6 Series has two low connections to the bottom center of the rad. Easy to pipe to. Pricey. If you want the pleasure of radiant panel heat and piping is underfloor, sometimes you have to be willing to look at plumbing! Sometimes the resulting comfort of panels makes customers' "vision adjust." This winter I installed 35 Mysons in three diff. houses. All working stellar.

That's why I asked about chrome covers, whether for copper or PEX. To me its a more appealing look... Plan was to home run with 1/2" PEX and maybe transition to 1/2" copper before coming thru floor. However I've only seen chrome covers ~ 4" in length, such as this: http://www.supplyhouse.com/Wirsbo-Uponor-F5600500-Chrome-Finishing-Sleeve-for-1-2-PEX-11-16-OD-4273000-p

I was focused on the "plain" panel radiators, like Myson Select or T6, Buderus, HA and DiaNorm. As far as pricing, they all seem about the same, except for Myson Select and Hydronic Alternatives which are less.

The "downside" of Myson Select is no bottom connection, but pricing is better.

Is the TRV more or less effecitive when mounted low, i.e. at the bottom of radiator (closer to floor) vs. top of radiator? Your right, I do not want to bend over to the floor to adjust the TRV and that wouldn't look good.

Which Myson's you install, Select? Plumbing thru wall or floor? Piping, PEX or copper? TRV mounted up high or low? Covered exposed piping to radiator or not?

SWEI

TRV needs to be high if at all possible. We use mostly Select (lots of sizes, nice price) with a few T6 where they owners really care about hiding the pipes. One or two of the fancy models per year if I had to guess. Be sure to factor in the appropriate derating when you size. If you balance the system properly, you will often be able to eliminate TRV's from 50% or more of the rads.

bmwpowere36m3

SWEI said:

TRV needs to be high if at all possible. We use mostly Select (lots of sizes, nice price) with a few T6 where they owners really care about hiding the pipes. One or two of the fancy models per year if I had to guess. Be sure to factor in the appropriate derating when you size. If you balance the system properly, you will often be able to eliminate TRV's from 50% or more of the rads.

Yeah I was sizing at 160-140F SWT/RWT. T6 are more expensive but doesn't seem by a whole lot (maybe if you have a large job). If my rough plumbing was in the walls, I'd totally go for the Select.

With thru the floor piping, TRV on top I would end up with ~30" of piping up to the fitting/TRV... Well, life is about compromise

I'd be nice if the T6 were offered in single convector... that way I could install ones as wide as the windows without either paying $$ or using really short panels.

bmwpowere36m3

How important is it to maintain a 2-4 fps flow thru the hydronic system comprised of panel radiators, PEX manifold, P/S piping and Mod Con boiler?

Given my heat loss figures per room, I figure with a delta T of 20*… I only need 0.55 to 0.7 GPM (per room/radiator).

If I go with 1/2" PEX, that'll be a flow rate of ~1 fps and that'll only get worse as the outdoor temp goes up from design day. Is it something worth worrying about?

I figure my longest run from the manifold is ~50-60', so factoring supply + return ~100-120'.

Rich_49

.55 gpm is about 1.835 ft/s & .7 is 2.33 ft/s . I would not worry too much about it though since when the TRV is near closed and as it is closing and opening you will often find your fluid lower than the standard which honestly needs to be brought up to date and recognize the tech we regularly employ at present . That rate was probably necessary with old air scoops but nowadays air bubbles hardly escape a quality air separator . Many radiant circuits also flow VERY LOW flows and I have not experienced an air problem in quite some years .

bmwpowere36m3

Rich said:

.55 gpm is about 1.835 ft/s & .7 is 2.33 ft/s . I would not worry too much about it though since when the TRV is near closed and as it is closing and opening you will often find your fluid lower than the standard which honestly needs to be brought up to date and recognize the tech we regularly employ at present . That rate was probably necessary with old air scoops but nowadays air bubbles hardly escape a quality air separator . Many radiant circuits also flow VERY LOW flows and I have not experienced an air problem in quite some years .

Based on Viega's literature, for barrier PEX I figure:

• 1.1-2.2 GPM for 1/2" PEX
  
• 0.6-1.2 GPM for 3/8" PEX
  

Based on the flow rates, I figured I'd home run 3/8" PEX… but,

when I ran it through TACO's circulator sizing guide, the head loss was HUGE! Then I double checked Viega's specs and the head loss should be about half.

Maybe the sizing guide is old and inaccurate values for PEX tubing.

Rich you saying I shouldn't be too concerned with the 2-4 FPS in the emitter loops? What about the P/S piping and thru the air separator?

hot_rod

Probably most if not all panel rads or Euro origin, or sold there are now tested and certified to EN442. This is a performance test based on flow and of course temperature.

The 2fps has to do with the ability of the fluid to carry along and air, even micro bubbles. To get the best performance all the air needs to be scrubbed from the system. Also the ability of the fluid to transfer the energy to the radiator is based on the min. flow velocity.

I agree there is some wiggle room, stay close to what the manufacturers suggest if you want the performance they have certified to the EN standard.
Not much available in tube size between 3/8 and 1/2 unless you get some metric sized tube, you need to decide which size will move the adequate amount of energy across the conditions your system encounters.

Buderus has a great panel rad calc pdf, and plenty of info online regarding various types and brands of rads and the sizing they recommend.

http://www.buderus.us/files/201003040246150.Panel_radiator_design_manual_12.2009.pdf

bmwpowere36m3

hot rod said:

Probably most if not all panel rads or Euro origin, or sold there are now tested and certified to EN442. This is a performance test based on flow and of course temperature.

The 2fps has to do with the ability of the fluid to carry along and air, even micro bubbles. To get the best performance all the air needs to be scrubbed from the system. Also the ability of the fluid to transfer the energy to the radiator is based on the min. flow velocity.

I agree there is some wiggle room, stay close to what the manufacturers suggest if you want the performance they have certified to the EN standard.
Not much available in tube size between 3/8 and 1/2 unless you get some metric sized tube, you need to decide which size will move the adequate amount of energy across the conditions your system encounters.

Buderus has a great panel rad calc pdf, and plenty of info online regarding various types and brands of rads and the sizing they recommend.

http://www.buderus.us/files/201003040246150.Panel_radiator_design_manual_12.2009.pdf

I've looked at that document, nothing in it stipulates flow rates... other than satisfying heat load. No examples of home-run piping and their examples are radiators in series.

They do sell 3/8" pex connectors, but don't list 3/8" PEX their pipe sizing table. However they do chart pressure drop vs. GPM and the curves go down to 0.06 GPM...

bmwpowere36m3

EN442:
As per January 1st 2002, Belgium, the Netherlands and Luxemburg will also use EN 442. Across Europe, one uniform method of determining heat outputs of radiators and convectors is used. This new norm measures heat output at a supply temperature of 75°C, a return temperature of 65°C and a room temperature of 20°C. This means an overtemperature (= average difference in temperature between object and the environment) of 50 degrees Celsius.

No mention of GPM requirement, just SWT/RWT and delta T. Obviously smaller radiators would need less GPM to satisfy the delta T.

bmwpowere36m3

That’s why I'm asking... in a home-run setup, with at least a delta t of 20*, you'd need an emitter outputting 10k to get 1 GPM. Yet guys talk about 30 and 40 delta Ts… the flow rates must be snail-like, unless they have very, very, very large radiators.

Anyhoo, it looks like running 3/8” PEX will at least keep me around 2 fps (theoretically, we know how that goes….).

SWEI

This has a lot of useful info in it.

bmwpowere36m3

SWEI said:

This has a lot of useful info in it.

I know you do a lot of these panel installs... the 3/8" can supply the BTUs and GPM, but the head loss adds up. Longest loop ~ 120 ft and about 10 ft of head (just tubing)... seems a little high. More than a Taco 007 can handle and Grundfos Alphas highest constant pressure setting is 12 ft. I bet there are another couple feet of head loss in the radiator, manifold and secondary piping.

It all goes back to whether maintaining a min of 2 fps is really that critical? Seems with radiant flooring the GPMs are really small, yet they use 1/2" PEX usually... right?

bmwpowere36m3

From PEX universe:



Based on those flow rates and PEX sizing, the water velocity ~ 1 fps. Do people with radiant floor systems suffer from air locks, air separator issues, insufficient heat transfer or other issues?

bmwpowere36m3

Another example is Uponor's Radiant Floor System Guide,

1/2" PEX, 0.6 GPM

I know, I know this is radiant flooring… and I'm interested in another system. I'm probably over-thinking this

hot_rod

I agree, you're over-thinking it.

bmwpowere36m3

@SWEI‌

Dude, you are the man!

I just looked at that document again. 3/8" hePEX is rated at 3.95' per 100 ft of tubing (0.6 GPM, 2 fps, 140F). I can totally work with that. I'm emailing them to confirm.

Good thing I looked at that again. I was looking at ViegaPEX and Wirsbo values from a grundfos technical document. Those numbers were closer to 6'. I think I also made a mistake when first calculating the head loss. Sometimes you need to take a second look

Rich_49

Nobody said they would be easy to size . They really are not all that difficult though . Your manifolded home run system appears on page 23 and is referred to as Multiple one pipe system . For sizing flows and all that good stuff you'll find work sheets and instructions on how to do the calculations and choose SWts and the proper Delta Ts for fluid as per Buderus . Don't get confused by mention of Delta t on page 19 , Table 9 . These are the Delta between the system water temp and desired room temp . So a Delta of 100* on this chart would mean a SWT of 165* with a room setting of 65* . Wish you well .

GW

Unfortunately hair splitting is required when room temps are a factor. As room temps increase the dT decreases. We can try all day long to aim for a certain design, but throw in the real world and it just gets wobbly.that is a nice document though, very thorough.

SWEI

Uponor has a ton of great info on both plumbing and heating applications. There's a chapter in the CDAM with numbers for 30%, 40%, and 50% glycol and also 5/16" PEX (which I've never personally seen, but they do sell it.) As far as friction loss goes, any SDR9 PEX will have the same performance. Do note that the fitting loss numbers are specific to their products (which use ASTM F1960 cold expansion.) Standard ASTM F1807 crimp fittings are significantly more restrictive.

Don't miss the PDAM either.

SWEI

bmwpowere36m3 said:

I know you do a lot of these panel installs... the 3/8" can supply the BTUs and GPM, but the head loss adds up. Longest loop ~ 120 ft and about 10 ft of head (just tubing)... seems a little high.

10 ft would be way high for a residential job in my book. I would look at reverse return and/or split manifolds to keep the 3/8" runs shorter.

It all goes back to whether maintaining a min of 2 fps is really that critical? Seems with radiant flooring the GPMs are really small, yet they use 1/2" PEX usually... right?

It's nice to keep the velocity up when you can. The overwhelming majority of RFH jobs we see which were done using 1/2" PEX could easily have been done using 3/8" PEX at the same head loss with a bit of planning. It costs about 12% less on a per-foot basis but it's much easier to work with -- especially with tight tube spacings (and even more especially if you're trying to install it in cold weather.)

RobG

SWEI said:

Uponor has a ton of great info on both plumbing and heating applications. There's a chapter in the CDAM with numbers for 30%, 40%, and 50% glycol and also 5/16" PEX (which I've never personally seen, but they do sell it.) As far as friction loss goes, any SDR9 PEX will have the same performance. Do note that the fitting loss numbers are specific to their products (which use ASTM F1960 cold expansion.) Standard ASTM F1807 crimp fittings are significantly more restrictive.

Don't miss the PDAM either.

The 5/16" is used for Quick-Trak. I would guess that they only make it so that you have to use their product with it.

bmwpowere36m3

Uponor/Wirsbo has some conflicting head loss #'s from their documents for the same sized "PEX" and conditions. Monday I'm going to confirm with their tech.

Seems like for radiant floor applications, loop-lengths, flow rates and delta ts are a different ball game... Flow rates are much lower and seem to result in velocities around 1fps.

bmwpowere36m3

FYI, I spoke with a tech at Uponor and here was his response:

Hello Mike- Since the 7th edition CDAM came out we have been aware of this issue. Since then we have come out with a radiant friction loss calculator available to use for free on line (linked below). This is the tool I use to assist customers over the phone and should be the most accurate.

http://www.uponorpro.com/calculator/#

Basically stating the pressure loss tables are inaccurate, not just in the CDAM... but other related Uponor documents.

bmwpowere36m3

Any recommendations for O2 barrier "PE" piping for the panel radiators and for over the top radiant (bathroom, aluminum xfer plates, sandwich between subfloor and tile)?

PEX-a/b/c, PE-RT, PE-AL-PE… Is there any real difference between PEX and PE-RT?

Locally I think I can get 3/8" in either Uponor (PEX-a) and Roth (PEX-c, PE-RT or PERT-AL-PERT)

SWEI

PEX-a where you need it to bend, PEX-Al-PEX where you want it to stay straight without a lot of support (radiator risers come to mind.)

Gordy

Pex al pex in plate installs keeps expansion noise in check along with constant circulation.

SWEI

Better brands of barrier PEX have an anti-squeak outer layer on top of the EVOH. It works.

bmwpowere36m3

SWEI said:

PEX-a where you need it to bend, PEX-Al-PEX where you want it to stay straight without a lot of support (radiator risers come to mind.)

It'll need to come thru the floor... I've never worked with PAP, but I'd imagine in 3/8" and 1/2" it should bend fairly easily no? I need a few bends, but not many... basically stringing it along floor joists and up thru floor.

I'd like it to stay "fairly" straight, look clean/neat.

I've only found ROTH carrying 3/8" PAP. Uponor, ROTH, Viega barrier PEX has a layer of PEX on the outside (protecting the EVOH layer).

hot_rod

I have seen cover tubes for the pex to protect and give it a nicer look above the floor. Chrome and white are common, I suppose you could paint any color.

If a section of the pex is exposed it should be protected from UV.

All in all transition to copper tube below the floor then paint or polish the copper that is exposed, simple and durable.

You can find compression or sweat fittings for copper to radiator.

3/8 or 1/2 pex would be my choice. If you want real flexible, look at Mr Pex tube.

If you want stiff, I like the FostaPex from Viega, it does require special tools to strip the outer layer, and only their fitting should be used.