Document zz4Mn5xzmxRJb2eQkd8nNY597
,490 CHAPTER 19 ;.,; ;:'<i i ,1958 Guide
feeder ducts of the radial system extend directly from the subfloor plenum
to the perimeter diffusers, and there is no loop' duct arbund'the perimeter
of the floor., The feeders do provide floor-warming, but not ^to the same
degree provided by the feeder and loop ducts'of'a' perimeter-loop system.
The same considerations of slab construction and edge insulation apply to
both systems.'
\
A simplified design procedure6 using 6-in. diameter duct and subject.to limitations of : 1,000 to 1,200 sq ft maximum area, not more than approxi mately 15 ft along perimeter between diffusers, and no radial duct sub stantially longer than 20 ft, is'the following:
1. Calculate the heat loss of each room or area using the method explained in Chapter, 12. For subfloor and edge losses, see8 Manual 3 of the National Warm Air Heating and Air Conditioning Association.
2. Determine the required furnace-bonnet capacity from the heat loss.of the building.
3. Locate the diffusers on the plan. Allow at least one diffuser for each exposed wall in each room or area of the building and preferably beneath window areas.' For
Fig. 6. Pebimeteb Radial System with Feedeb Ducts in Concbete Slab ob Cbawl Space
residential installations, limit each diffuser to a maximum of 7,000 Btuh. This is a preliminary estimate of the number of diffusers needed.
4. Measure the length and count the number of elbows in each feeder duct. De termine Btuh capacity of each feeder duct from Table 3. Use Table 3 (Section A) for sidewall ind floor diffusers and Table 3 (Section B) for baseboard diffusers.
5. If the total Btuh capacity of all feeders to each room or area equals or exceeds the heat loss of that room or area, the number of feeders initially chosen is satis factory. If the heat loss exceeds the Btuh capacity of the feeders, use and locate additional diffusers and feeder ducts.
6. The cfm values in Table 3 are used for designing the return-duct system.
Perimeter-Radial System in Crawl Space or Basement Construction
The perimeter concept of warm air heating has been applied- to crawlspace and basement homes by locating the diffusers in the perimeter loca tion and by warming the area underneath the floor of such, structures. Although the construction of the crawl space and the foundation wall is the responsibility of the architect and the general contractor, it is impor tant that the engineer check the construction to make certain that it will not adversely affect the performance of the heating system. Details on crawl-space construction are shown6 in Manual 4 of the National. Warm
Warm Air Heating Systems
491
Table 3. Btuh Capacities and CFM of 6-Inch Feedeb Ducts in PebimetebRadial Systems in Concbete Slab Floors
SECTION A. FOR SIDEWALL AND FLOOR DIFFUSERS
Bonnet Pressure 0.15 *'n. Static
Bonnet Temperature J70 F
Actual Length op Pipe from Bonnet to Diffuses--Feet
Elbows Capacity 5 10 15 20 25
30 35
40 45
50 55
60 65
70 75 .80
0 Btuh Cfm
1 Btuh Cfm 2 Btuh
Cfm 3 Btuh
, Cfm 4 Btuh
Cfm 5 Btuh
Cfm 6 Btuh
Cfm
8700 8060 7460 6920 6430 5960 5550 127.7 124.8 122.3 119.7 117.4 115.0 113.0 8620 8000 7430 6900 6400 5930 5500 5100 122.8 120.0 117.6 115.3 113.0 111.0 109.0 107.3 8600 7960 7390 6860 6380 5940 5530 5150 4800 118.5 116.2 114.0 112.0 110.0 107.8 106.0 104.5 103.0 \ 8640 8020 7450 6950 6460 6020 5600 5200 4850 4500 114.0 112.0 110.0 108.2 106.5 104.7 103.0 101.4 99.6 98.0 8760 8160 7580 7050 6540 6080 5640 5250 4880 4550 4250 110.2 108.4 106.6 105.0 103.0 101.5 100.2 99.0 .97.5 96.0 94.6 8850 8250 7670 7140 6640 6170 5740 5340 4960 `4620 4290 3990 106.8 105.0 103.5 102.0 100.5 .99.0 97.5 96.0 -94.6 93.4 92.0 91.0 9050 8420 7840 7280 6750 6300 5850 5440 5060 4700 4370 4060 3760 104.0 102.5 100.7 99.2 97.8 96.5 95.3 94.0 92.6 91.4 90.0 .88.7 .87.6
The Equivalent Length Values used and included in calculating this table are: Diffuser and Boot = 40 ft;
Plenum Takeoff = 20 ft; Each Elbow *= 14 ft. For each additional 14 ft equivalent length of boot and diffuser,
count one additional elbow.
./?.
All cfm values are based on standard air.
SECTION B. FOR BASEBOARD DIFFUSERS ONLY
Bonnet Pressure 0.15 in. Static
Bonnet Temperature 170 F
No. OF Elbows
Capacity
Actual Length op Pipe from Bonnet to Diffuser--Feet
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
0 Btuh Cfm
8570 8000 7450 6910 6420 5960 5560 5150 4800 4450 4160 109.0 107.2 105.5 103.7 102.0 100.4 98.8 97.5 96.1 94.8 93.5
1 Btuh Cfm
8700 8100 7550 7000 6520 6060 5630 5250 4860 4530 :4220 3930 105.5 104.0 102.3 100.7 99.2 97.6 96.2 95.0 93.6 92.3 91.1 90.0
2 Btuh ' Cfm
8890 8270 7700 7160 6660 6200 5750 5350 4980 4620 4300 4000 3700 102:8 101.3 99.8 98.2 96.7 95.3 94.0 92.7 91.5 90.2 89.0 87.8 86.5
3 Btuh Cfm
8440 7870 7320 6820 6350 5880 5460 5070 4700 4350 4020 3710 3440 98.4 96.8 95.3 93.9 92.5 91.3 90.0 89.0 88.0 86.9 85.8 84.7 83.5
4 Btuh Cfm
8690 8080 7500 6980 6500 6030 5580 5180 4800 4450 4120 3820 3520 3250 95.8 94.4 93.0 91.6 90.3 89.0 87.8 86.7 85.7 84.6 83.7 82.6 81.6 80.5
5 Btuh Cfm
8940 8320 7740 7200 6680 6190 5720 5320 4920 4550 4220 3890 3600 3350 3100 93.4 92.2 91.0 89.8 88.5 87.3 86.2 84.8 83.8 82.8 81.7 80.8 79.9 79.0 78.0
6 Btuh Cfm
8580 7960 7380 6850 6350 5880 5440 5040 4660 4320 4000 3670 3400 3150 2930 90.0 89.8 87.6 86.5 85.5 84.2 83.1 82.0 80.9 80.0 79.0 78.0 77.3 76.5 76.0
m iaaeou = 20 ft; Each Elbow = H U3er count one additional elbow.
All cfm values are based on standard air.
le are: Diffuser and Boot * 100 t equivalent length of boot and
Air Heating and Air Conditioning Association. The crawl space or base ment should be heated to provide warm floors.
A simplified design procedure6 for an individual duct system is summanzed as follows:
qiA' peculate the heat loss of each room or area using the method explained in Pter 12. Consider the basement or crawl space as a part of the structure and