Panel Rad design

Dave_22

I had a good thread on here a month or two back on Panel Rad's and TRV's. I now have another question-In a homerun system, what are the pluses and minuses if I were to design with a large (40 deg) delta T OR if I design with a lower supply temp with a smaller delta T?? If I designed both ways for a return temp of 130 lets say- what would be each plus and minus?? Thank you for your comments.

Mike T., Swampeast MO

All other things equal, if you design for a higher delta-t you'll need less circulation power, but higher supply temp to maintain the same average temp in the rads. With 130° return and 40° temp drop, supply would be 170° with an average rad temp of 150°. Select your rads to give your design requirement at 150° average temp. Note that this will require slightly smaller panels than if 20° delta-t were used (average rad temp in this case would be 140°). Good things: Besides the reduced circulation power, you might save a bit on panels. Bad things: your supply temp is higher and efficiency will most likely drop (particularly with a condensing boiler) as the system approaches design conditions. Also, there appears to be a direct relationship between lowered panel temp and increased comfort.


If you don't want to increase supply temp with the higher delta-t, then you have to increase rad size so that you get the same output ability at the lower average temperature. Say you wanted a design supply temp of 150°. With 40° temp drop, your return would be 110° and average rad temp of 130° and you'd side the rads accordingly. Advantages are reduced pump requirement, increased efficiency (particularly with a condensing boiler) and increased comfort. Only real disadvantages are increased cost of the panels and perhaps difficulty in placement because of increased size.

Note that in actual operation your design temp drop may rarely if ever stay constant at your design level. The TRVs will vary the delta-t to suit the current load on the system and can be further manipulated by the reset curve.

G. Gibbs

Tool

Here is a great tool for Dianorm Rads...If you use a new Taco Delta-T circulator you may be able to keep more of a constant temp. diff. I was just shown the new circulator last week. Greg

G. Gibbs

Delta T & Panel Rads.

I've attached a great sizing spred sheet for Dianorm Rads. It will show you the btu outputs based on delta t's...
Our local Taco rep. Billy Garnett just showed me the new
"delta T" circulator they have on the market...I think I'm going to give it a go on our new building. I've attached a drawing, P-1 will be the delta-t circulator, I've designed a 30 deg drop in our Rads. 165-135. I will let you know how
the circulator does. Greg