Panel Radiator piping

Tim Davis

Iam looking for some ideas on piping multable radiators using thermostatic radiator valves.

Thanks TD

Tim Davis

Panel Radiator piping

I am looking for some ideas on piping multiple radiators using thermostatic radiator valves.

Thanks TD

kevin

how many rads?

I am in the LONG process of putting in a new system in my house.I am using Buderus rads and using TRV piped from a manifold(s). Thee was a great artice by John Siegethaller a while back in P&M. Hot Rod might have the proper reference. kpc

Tim Davis

Kevin, there will be 5 total I have seen these piped using moniflow Tees but not sure how this works.

Thanks
TD

ChrisL

Here's the link on a good article for panel rad piping options: http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,23759,00.html

Chris

Mike T., Swampeast MO

Buderus

"Panel Radiator Design Manual" available in .pdf format at their website is REALLY good.

TRV'd panels are best installed two-pipe. START with a well-designed two-pipe system WITHOUT considering that TRVs are installed. Then just add the TRVs--you don't need any piping changes at this point.

Since TRVs strive to MAINTAIN setpoint while giving the ability to control each space independently, they really want constant circulation for best operation.

TRVs and constant circulation go hand-in-hand with outdoor reset. If you don't use reset and just keep the supply temperature at the level required for design heat loss, you can and will wind up with situations with very low flow/very high delta t so you have to be VERY mindful of the potential for low return temperature.

Personally, I would design the sytem with a condensing boiler and size the panels such that return temp is expected to be at/below 140° at least 80% of the time. While the condensing boiler costs more, the near boiler piping is GREATLY simplified and you can very often use only a single circulator and a differential pressure bypass valve. Such a design will cost a bit more up front (the condensing boiler and possibly somewhat larger panels) but it will be simple enough that any reasonably-qualified technician can trouble-shoot easily. I'm also firmly convinced that lowered supply temperature equates directly with both increased efficiency and increased comfort.

Regarding the reset: The output of panel radiators is reasonably linear. If you have done your heat loss calculations well and balanced your radiation carefully, the supply temperature requirement will be quite linear as well. Remember that one of the BIG benefits of TRVs is the ability to keep some spaces significantly warmer (BR when you're sick, baby's room, grandpa's room, etc.) so even with "perfect" calculations you want water about 10° higher than truly necessary--if the calculations were truly perfect, it would be impossible to raise the temp for lack of supply temp. This "headroom" in the reset curve will also allow somewhat quicker recovery if you're setting TRVs down during periods of vacancy.

I mean no disrespect to the mfgrs of electronic reset controls here, but if the "headroom" requirement is greater than the deviation from linearity of the heat emitters in most of their useful output range, you really need nothing more than a mechanical reset (base and ratio adjustable) UNLESS you're producing DHW or have some other special requirement.

One last thing. When computing heat loss, be VERY picky paying particular attention to ceiling construction. If using HVAC-Calc, use about 80-85% of the heat loss reported for your panel sizing, but use the "real" number for sizing the boiler. This effectively "builds in" your headroom.

Sorry, still not done...

If you have sized and controlled this way it is practical to add small radiantly heated areas with reasonable exposure controlled with the acme of simplicity--simple balance valves at supply/return connections at the mains. No t-stat, no 2-or-more-way valve, etc. You must though CAREFULLY choose your method of transferring heat to the floor to work with the available supply curve.