Boiler Selection on a Panel Rad system

rjwinz

All, we want to install panel rads and a hw boiler in a late 70s split foyer in Minnesota. I hope to install the panel radiators and run the pex to the boiler room and find a good contractor to install the boiler and near boiler piping, pumps, tank, etc. I will do a heat loss calc and size the rads accordingly. My main question is what HE boiler and what water temp? Simple system with home runs to each rad off a manifold. Panel rads seem to get derated significantly below 180 degrees, so they will have to be upsized accordingly. We need a direct vent boiler. They seem to go all the way from the cast iron WM GV90+, up to the most efficient mod con. I will hire a contractor but I want the Wall's help first. Thanks for any suggestions as to water temp and model of boiler.. PS, house is baseboard electric, so any hw system will be an improvement. Edit: I understand that the contractor is more impotant than brand. That said, this is Not hot water heat territory and your suggestions and information will help. I used you guys and Dan's books to learn about and tune my steam heat system.

Jamie Hall

The output of any radiator -- panel or otherwise -- drops with the temperature of the radiator. If you want to get higher efficiency from a high efficiency boiler than you would from a regular boiler, the return temperature has to be less than about 140 -- and the lower the better.

Therefore... step 1, as always, is to determine the heat loss of the space for each radiator. Step 2, assuming you want to maintain high efficiency, is to size the radiation assuming a water temperature low enough to get at least some condensation -- using a more or less normal delta T of 20, that would imply that the radiator is sized for a temperature of 150 (which would give you 160 in and 140 out).

Now having done that, if you do use a mod/con and use outdoor reset, you should be getting pretty good high efficiency. But I'm not going to suggest a boiler. Rather, I would say to do yourself a real favour and use a boiler which your installer is familiar with and which he or she likes to work with and maintain -- because an HE boiler does take a fair amount of careful and intelligent maintenance.

rjwinz

Thanks Jamie. BTW we currently have a historic home with a Burnham IN8, vaporstat running under 8 ounces. I understand steam heat. Hot water heat, not so much.

hot_rod

Here is some math to show derate number crunching

mikeg2015

Just size for 160F water, 140F return at design as a compromise and use outdoor reset and 95% of the time I’ll bet you need 130F or lower.

You can also design to a 30F delta T but using lower flow rates. Further, you could use cheap baseboard radiators piped in series with the panels (warmest) and again, get a 25-30F delta T for economy.

Efficiency is all about return water temp, not supply water temp. If the boiler will tolerate a 50F delta T, you could make 150F water and be 95% effecientt with 100F return temp.

If you have an high efficiency (ECM motor. Can be retrofitted cheaply and easily) air handler for AC, you could add a hot water coil and pipe that in series and run at at 50% speed and use that as a 2nd stage in coldest weather. Use outdoor reset on return water temp so it will modulate up when there’s a call for 2nd stage.

With high mass radiant, I like Combi boilers or indirect tank. Tank type gas water heater as all junk now it seems with the low NOX and and flame arrestor filters and race to the bottom on price and quality.

ch4man

whats currently heating the late 70's split foyer?, it cant be the IN8.......

edit, i see its electric BB, where in MN (my home state) is a late 70's house is an all electric house?

rjwinz

ch4man, on a hill over the Mississippi near Winona. Electric baseboard. Looks to be a Wisconsin built modular from 1977. OK construction, poured concrete foundation.

rjwinz

Mikeg2015, kindly explain your comment about using baseboard with panels. Do you mean run the return out of the panel through a section of bb to further lower the return water temp?
Thanks

Jamie Hall

rjwinz said:

Mikeg2015, kindly explain your comment about using baseboard with panels. Do you mean run the return out of the panel through a section of bb to further lower the return water temp?

Thanks

That's what I read it as, and it's not a bad idea at all -- good way to extract some more heat, get a bigger delta T -- and get your return temperatures down and efficiency up.

jumper

Are you going to switch whole house to hot water heat? For only one room hot water sounds expensive.

rjwinz

Whole house. About 12-14 panel rads. Some of the electric bb will stay for backup.

rjwinz

> @Jamie Hall said:
> Mikeg2015, kindly explain your comment about using baseboard with panels. Do you mean run the return out of the panel through a section of bb to further lower the return water temp?
>
> Thanks
>
> That's what I read it as, and it's not a bad idea at all -- good way to extract some more heat, get a bigger delta T -- and get your return temperatures down and efficiency up.

It is an interesting idea. Not sure what my wife would say. Lol.

Brewbeer

i did this a few years ago, except i used baseboards instead of panel rads. If you do a room by room heat loss calc, and put the results into a spreadsheet, you can vary supply temps and see how that impacts the amount of panel radiation that you need to meet the load. I used a design day supply temp of 130F.

clammy

If you install a cast iron direct vent boiler w a max temp of 167 your panel rads will be fairly competive in price for what your getting and semi zoning But as you start de ratting them for condensing equipment it will cost a lot more .i know this I used135 @10 ot and I spent a decent amount on 5 model 22 24 x 36 to meet my heat lose for a few rooms I also have some cast iron base and 2 panel rads .the rating at hi temp are fairly decent and add trv to balance it out .i used 1/2 pex al pex and a uponor 8 port w flow balancers for a pump I used a wilo pd ecm .i wouldn’t hesitate to install those type of systems on a hi temp or low temp as long as there sized for the heat lose and the water temp .i think they look much better then baseboard they blend into the room and don’t get as dusty and beat up plus you get back your base mounding .i did a mid temp w a wall hung a few years ago with about 15 panel rads and a buffer tank constant circ using a temperture averaging stat worked out great best of luck on your endeavors peace and good luck clammy

jumper

Interesting idea. Ceiling height panels at high temperature in series with low level ones for big delta T. You can use smaller tubes as well as higher efficiency from boiler. I think we can go too far to save energy.

mikeg2015

rjwinz said:

Mikeg2015, kindly explain your comment about using baseboard with panels. Do you mean run the return out of the panel through a section of bb to further lower the return water temp?

Thanks

Yes I mean to either run them in series sequentially or in 2 independent circuits in series. Whichever is easier to pipe.

Ceiling panels are problematic because air temps are already 80+ at the ceiling so capacity is diminished and there little connection generated.

Other option is hydronic air handler in series as mentioned.

rjwinz

Thanks. We would mount the panel rads under windows if possible. The ones on the lower level would be fed from the ceiling and might sit nicely on the knee wall.

At the moment I am struggling whether to go with a mod con or a cast iron boiler with a power vent. Or that WM gv90+ thing which appears to be a cast iron boiler with an add on secondary heat exchanger. Goal is comfort. Any of them will beat electric bb for cost of fuel.

rjwinz

Should add that another goal is low electrical power usage so i can design a battery backup system to run it during an outage. I have a 12v 460 amp system with an 1800w inverter for my current steam boiler, cpap, wifi, etc. As such, looking at ecm circs.

hot_rod

rjwinz said:

Thanks. We would mount the panel rads under windows if possible. The ones on the lower level would be fed from the ceiling and might sit nicely on the knee wall.



At the moment I am struggling whether to go with a mod con or a cast iron boiler with a power vent. Or that WM gv90+ thing which appears to be a cast iron boiler with an add on secondary heat exchanger. Goal is comfort. Any of them will beat electric bb for cost of fuel.

I think all the mod cons will have a much more robust control, compared to cast iron. The modulation alone is worth the cost, even if you are not always condensing.

rjwinz

Thanks Mr. Rohr. What reading can I do to learn more about hw heat? Do i start with Siegenthalers textbook?

hot_rod

rjwinz said:

Thanks Mr. Rohr. What reading can I do to learn more about hw heat? Do i start with Siegenthalers textbook?

What part of hydronics? Here are 24 free downloads covering most parts of hydronics. #12 is a Fundamentals, #15 shows some of the most current piping schematics. And everything in between. Sign up to receive the hard copies twice a year.

https://www.caleffi.com/usa/en-us/technical-magazine

rjwinz

Thanks much. Time to start reading.

SuperJ

Panel rads, outdoor temperature setpoint reset, TRVs and a constant circ delta p pump will keep your return water temp low and delta high. You'll want a tightly sized modcon with a lot of turn down or a buffer tank though. Do this and you have good results even if you size for 160f.

IMHO, I think it makes sense to size for a max of 140f SWT. But go lower if you can afford the space and $$$ for max efficiency and future heat source compatibility. I sized for 140f but found I actually run a bit higher due to some bad windows, but even with 150f water my mixed (from all zones) return rarely exceeds 100degf. Individual zones might be over 120-130degf at times but my other generously sized other zones keep my return low since the TRVs just throttle as the water temperature climbs as long as the zone temp is maintained. Often the top of the rad is hot and the bottom feels like room temperature, but the rad is nicely breaking the cold draft with minimal hot water flow and no off cycles.

Here's my return water temperature for the last month.