Engineering Design - Radiant Heating

     Radiant panel perimeter heating systems are very compatible to the modern building design.
The performance capacity and width of the radiant panel is directly related to the construction of the
perimeter wall where the panel will be located. All Sun-el performance ratings are based on a 70°
Fahrenheit room air temperature and a 70° Fahrenheit AUST (Average Unheated Surface Temperature).
Wall conditions that would lower the (AUST) will actually increase the panel performance. Therefore
Sun-el performance ratings are established at a level that are safe to use in nearly all types of
perimeter heating applications.

     The design of an extruded radiant panel system should follow with all the usual design considerations
for a closed water system. The following criteria are needed to proceed:

1. Establish the indoor design temperature.
2. Estimate the heat loss for the exposure zone or room.
3. Establish the heating water design entering and leaving temperature.
4. Determine the capacity of the radiant panel from the catalog by using the mean water temperature.
5. Calculate the area, width and length of the panel.
6. Calculate the flow rate of the panel.

All the design criteria can be based on the following standard formulas:

1. Heat Loss

Total BTU/HR / Lineal Foot of Panel = BTU/HR Required Per Lineal Foot

2. Panel Width

Req. BTU/HR Per Linear Foot / Panel Performance BTU/HR (from catalog) = Panel Width in Feet

3. Flow Rate in Gallons Per Minute

GPM = Total BTU/HR
* 500 x Water Temperature Drop. F
* Constant

The following design criteria will apply to this building example.
The building is multi-floor and, this example is based on an intermediate floor.

Building Criteria
• 80 Foot X 80 Foot Building Dimensions
• 12’0” – Floor to Floor
• Wall U = 0.15 BTU/HR Per SF – Per Degree Fahrenheit
• Glass U = 0.6 BTU/HR Per SF – Per Degree Fahrenheit
• Glass Height 5 Foot Continuous
• Average U = 0.33 BTU/HR SF – Per Degree Fahrenheit
• Outside Design = 0 degrees F Dry Bulb
• Inside Design = 72 Degrees F Dry Bulb

Calculated Heat Loss Per Floor
320 LF x 12’0” x 0.33 BTU/HR Per SF – Per Degree
Fahrenheit x 72 degrees F = 91,238 BTU/HR Total per Floor

Indoor Design temperature = 72 Degrees Fahrenheit
Supply Water Temperature = 200 Degrees Fahrenheit
Water Temperature Drop (WTD) = 20 Degrees Fahrenheit
Mean Water Temperature (MWT) = 190 Degrees Fahrenheit
Heat Loss Per Floor = 91,238 BTU/HR

1. Calculate the Heat Loss Per Lineal Foot of Perimeter Wall

91,238 BTU/HR Total / 320 LF of Wall = 285 BTU/HR Per Lin. Ft. of Wall

2. Determine Length of Extruded Panels.

     Standard panel lengths are available in 10 foot to 16 foot lengths : Select lengths most compatible
to room dimensions or column spacing. (For example : A 20 Ft. center line to center line of column
dimension will use two 10 Ft. panels between columns.)

3. Calculate the Width of Panel Required.

     Sun-el Extruded Panels are available in various surface configurations.
Fluted face (ELF), V-Groove(ELV), or Smooth(ELS) face patterns will have the same
performance ratings. Select the face pattern desired by the architect or building owner.

     The performance curve for Extruded linear series will produce 290 BTU/HR per sq. ft. with
a 190 degree MWT.

Therefore, the panel width will be as follows :
285 BTU/HR Per Lineal Foot Required / 290 BTUH/HR Per Square Foot Panel Capacity = .98 Foot Wide

Therefore, a 12” wide (2-6” Wide Extrusions) panel will meet requirements for this design.

4. Determine Flow Rate Required

GPM = ( Total BTU/HR ) / ( 500 x WTD )

Example :
91,238 / ( 500 x 20 degree F (WTD) ) = Total GPM per floor (9.12 GPM)

Conversion for Exposure.
22,810 BTU/HR Per Zone / ( 500 x 20 degrees F (WTD) ) = 2.28 GPM Per Zone

5. Establish Piping Design and Water Pressure Drop Per Circuit.

Below we will illustrate two scheme of panel circuit design.

      For this example, split an 80 LF exposure using four 10 foot panels in each circuit. Each circuit
will have 80 foot of copper tubing with 1.14 GPM per circuit. Referring to the Sun-el pressure
drop curve each circuit will produce a headloss of 1.9 foot.




Supply Water Temperature = 190 Degrees Fahrenheit
Water Temperature Drop (WTD) = 50 Degree Fahrenheit
Mean Water Temperature (MWT) = 165 Degrees Fahrenheit
Heat Loss Per Floor = 91,238 BTU/HR

At 50 degrees F WTD panel performance = 190 degrees F EWT; 50 degrees F WTD;
165 degrees F MWT; 200 BTU/HR per square foot.

Calculate Width Requirement

285 BTU/HR Require Per Lineal Foot / 200 BTU/HR Panel Capacity = 1.43 Foot Wide

Therefore, an 18” wide panel (3-6” Wide Extrusions) will be nearest width to wall loss requirements.

Calculate GPM

91,238 Total BTU/HR Per Floor / ( 500 x 50 degrees F WTD ) = 3.65 GPM Per Floor
.91 GPM Per Zone = 3.6 Foot Head