|
Design Reference for Heat Loss Calculation
This section gives a general idea to design a space heating system;
it can vary system to system and case by case.
Initial step in any heating system design is to determine the
heating requirements (same as ¡°heat loss¡±) of each individual room
or area. More accurate heat loss calculation is to assure the
potential of maximum energy savings and to achieve maximum level of
comfortness. By using the conventional heat loss calculations for
radiant heating design can result to over size the system.
As
an example, when desired room temperature is 65 ¡ÆF ~ 70 ¡ÆF and
ambient temperature is -10 ¡ÆF at seasonal
low temperature, following resistance to heat flow values can be
used for basic heat loss calculations in each construction site.
|
Constructed Components and Sections |
R Factor at -10 ¡ÆF Seasonal Temperature |
|
Ceiling |
R-19 Insulation |
5 |
|
|
R-30 Insulation |
3 |
|
|
R-38 Insulation |
2.5 |
|
|
Interior above Heated Ceiling |
0 |
|
Walls |
R-11 Insulation |
8 |
|
|
R-19 Insulation |
5 |
|
|
Interior wall between rooms |
0 |
|
Floor |
Un-insulated wood frame over a crawl space |
18 |
|
|
R-11 insulation |
8 |
|
|
R-19 Insulation |
5 |
|
|
R-30 Insulation |
3 |
|
|
Un-insulated slab on grade |
13 |
|
|
R-10 insulated slab on grade |
4 |
|
|
Interior between heated spaces |
0 |
|
Window |
Single Glazed |
80 |
|
|
Double Glazed |
40 |
|
Door |
1-1/2¡± Wood |
35 |
* More detail heat loss data can be collected from the heating
design software and heating design engineers.
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From above table, factor in areas as square feet to figure out heat
loss calculation (or required heat calculation and unit for the heat
requirement is BTU/hr in each section.
Pipe spacing in a radiant floor heating installation can directly
affect the heat output. The commonly recommended pipe spacing is
8¡± ~ 9¡± with ¨ö¡± PEX pipe. Also the typical pipe lengths are from
150¡¯ to 450¡¯ in each loop where pipe lengths can be calculated (in
each loop, heating area times by 1.3). For an example, if heating
area is 200 square feet, pipe lengths are approximately 260¡¯.
Finally calculating the each loop requires flow rate divides by the
total required heat output (BTU/Hour) by 500 times the design ∆T of
the system. A design ∆T of 28 ¡ÆF is considered optimum for
on-demand tankless water heaters.
Required
heat output (BTU/Hr) each loop
Flow Rate =
¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬¦¬
500 X ∆T
This is very rough formula to design a radiant heating system,
please consult you¡¯re your heating design engineer for more accuracy
of your heating system design.
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