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KRA
User Manual
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Keeprite KRA User Manual

Run Around Heat Recovery
PRODUCT DATA
Bulletin K70-RA-PDS-11
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www.keepriterefrigeration.com

GENERAL SELECTION INFORMATION

Quick Selection Data 8 Row Coils
AIR VELOCITY
Selection Charts show performance from 400 to 600 S.F.P.M. and are based on an 8 row deep coil. Low velocities result in increased recovery performance; however, coil size and initial costs will be greater.
FIN SP ACING
For standard Heating and Ventilation applications, a fin spacing of 12 fins per inch is recommended. For applications where heavy deposits of foreign matter are present, a fin spacing of 8 fins per inch should be used.
MASS FLOW RA TIO AND RECOVER Y F ACTOR
The mass Flow Ratio is:
Larger Air Flow (SCFM) Small Air Flow (SCFM)
The recovery Factor, Ra, (Fig. 1) is always for the smaller air flow. The Recovery factor, Ra, divided by the mass flow ratio equals the recovery factor, Rb, for the larger air flow.
APPLICA TION
SELECTION CRITERIA
This Run-Around cycle selection data is based on the following criteria:
1. 8 - Row deep coils only.
2. Sensible heat recovery only.
3. Glycol flow rate of 3 USGPM/Feed.
4. 50% Glycol solution.
5. face velocity and fin spacing is determined by the type of system, the degree of fouling expected and the general space limitations.
6. Ten basic steps are outlined to make a complete selection with all necessary air and fluid side data. However, Step 9 (fluid temperatures) may be omitted unless specifically required.
7. Coil row depths are the same for the exhaust and supply side with the fluid conditions balancing to suit.
8. Data based on minimum supply air temp. of 0 °F.
EXHAUST AIR TEMPERATURES
For exhaust air temperatures lower than 200 °F the recovery factor must be corrected accordingly as shown in Fig. 1, Page 5.
LIMITATIONS
The method of selection will result in an approximate capacity only. In the interest of simplicity, some degree of accuracy must be forfeited.
For more accurate selections for various row depths, consult the local KeepRite Refrigeration Sales Office.
TERMS AND DEFINITIONS
ITD = Initial temperature difference between supply and exhaust entering air, °F. ITD
= Initial temperature difference between entering
ff
supply air and hot glycol, °F.
ÄTs = Supply air temperature difference, °F. ÄTe = Exhaust air temperature difference, °F. ÄTg = Glycol temperature difference, °F.
Ä
=
g
SCFM = Actual air, cubic feet per minute. ACFM = Actual air, cubic feet per minute. M = Mass flow ratio. R
= Recovery factor for smaller air flow.
a
Rb = recovery factor for larger air flow. GPM = U.S. gallons per minute
Supply air temperature difference, °F Glycol temperature difference, °F
SAMPLE RUN AROUND COIL SELECTION
GIVEN: Exhaust Air: 20,000 A.C.F.M. (Actual Cubic feet per minute) at 200 °F.
5. BTU/HR AND PERCENT AGE HEA T RECOVERY
(a) Supply S.C.F .M. x Supply side ÄTs x 1.09
= 10,800 x 124 x 1.09 = 1,459,728 BTU/HR.
Supply Air: 10,000 A.C.F.M. at 0 °F .
NOTES: - Exhaust air is relatively clean
- Altitude is 2,000 ft. above sea level
- Glycol solution is 50% (by weight)
- Face velocity to be used is 400 F.P.M.
GENERAL REQUIREMENTS AND ASSUMPTIONS:
- 8 Row coils only (circuiting to be determined)
using 12 F.P.I. fin spacing.
1. CONVERT TO S.C.F.M.
(Air frlow at 70 °F, sea level) For exhaust air at 200 °F. Altitude density ratio is .75 (Table 1) Converted exhaust air flow is therefore 20,000 A.C.F.M. x .75 = 15,000 S.C.F.M.
For supply air at 0 °F. Altitude density ratio is 1.08 (Table 1) Converted supply air flow is therefore 10,000 A.C.F.M. x 1.08 = 10,800 S.C.F.M.
2. CALCULA TE MASS FLOW RA TIO (M)
Mass flow ratio =
Large Air Flow S.C.F.M.
Small Air Flow S.C.F.M.
M =
15,000
10,800
= 1.38
3. RECOVERY F ACTOR (Ra)
The Recovery Factor (Ra) for small air flow, using 12 F.P.I. fin spacing, 400 S.F.P.M. face velocity and mass flow ratio (M) = 1.38, Ra = .62 (Fig. 1, Page 5). Temperature Correction Factor =-1.0 The recovery Factor (Rb) for the large air flow =
M
Ra
=
.62
1.38
= .45
4. EST ABLISH LEA VING AIR TEMPERA TURES
Initial temperature difference (I.T.D.) is entering exhaust air temperature minus entering supply air temperature:
200 °F - 0 °F = 200 °F I.T.D.
(b) Heat Recovery Effectiveness
Supply Side ÄTs I.T.D. 200
=
124
= .62 = 62%
6. COIL SIZING AND SELECTION
Knowing the face velocities and the air quantities, the exhaust and supply air coil face areas can be determined as follows:
Exhaust Air Coil Face Area
15,000 S.C.F .M.
=
400 F.P.M.
Supply Air Coil Face Area
10,800 S.C.F .M.
Knowning the face areas required , consult Table 2 and select coils that will result in face areas as close as possible to those above. (Coil lengths should be approximately double the coil width for the most economic selection).
Exhaust Air Coil: Select a 45” wide x 120” fin
Supply Air Coil: Select a 45” wide x 90” fin length coil Face Area = 28.1 Sq. Ft.
=
400 F.P.M.
length coil Face Area = 37.5 Sq. Ft.
= 37.5 Sq. Ft.
= 27.0 Sq. Ft.
7. DETERMINING INITIAL MINIMUM GL YCOL G.P.M.
U.S.G .P.M. =
= 34 U.S.G.P.M.
Large S.C.F .M. X 1.09 x (M+1)
2M x 410
= 15,000 x 1.09 x (1.38 + 1)
(2 x 1.38) x 410
8. CIRCULA TING AND ACTUAL GL YCOL G.P .M. REQUIRED
The approximate number of circuiting feeds required may be determined by using the minimum glycol G.P.M. required (Step 7) and dividing by 3 G.P.M. / feed.
TEMPERA TURE DIFFERENCE ( ÄT)
(a) Supply side ÄTs = I.T.D. X (Ra) Recovery Factor
= 200 °F x .62
= 124 °F
(b) Exhaust side ÄTe = I.T.D. x (Rb) Recovery factor
= 200 °F x .45
= 90 °F
(c) Supply side leaving temperature = Supply air
entering temperature plus supply side ÄT
= 0 °F + 124 °F
= 124 °F
(d) Exhaust side leaving temperature = Exhaust air
entering temperature minus Exhaust side ÄT
= 200 °F - 90 °F = 110 °F
s
This is as follows: 34 = Approximately 12 feeds 3
Referring to Table 3, a 45” wide coil KWH circuiting has 15 feeds. The actual G.P.M. / feed would be
34
= 2.26. This is lower than the allowable minimum
15 of 3 G.P.M. / feed. In order to operate at the minimum G.P.M. / feed, the total
G.P.M. would be 15 x 3 = 45 G .P.M. This is the final G.P.M. that should be used.
e
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9. DETERMINING GL YCOL TEMPERA TURES
(This step may be omitted if not specifically required) (a) Find the glycol temperature difference (ÄTg) as
follows:
BTU/HR recovered (Step 5a) Final GPM (Step 8) x 410
= 1,459,728
= 79 °F
45 x 410
(f) Cold Glycol Temperature = Hot Glycol Temperature (Step 9e) minus Glycol ÄTg (Step 9a)
= 158 °F - 79 °F = 79 °F
10. DETERMINE FLUID AND AIR SIDE PRESSURE DROP
(a) Fluid Pressure Drop: Refer to Fig. 2, Page 5 and using 3 GPM / feed, the base fluid pressure drop can be read as 10.5 feet of water. The conversion factor for the exhaust air coil is 2.93 (Table 4) and 2.31 for the supply air coil.
(b) Find the approximate hot and cold glycol temperatures as follows:
Supply Air ÄTs (Step 4a)
Factor Ä
=
g
= 124
Glycol ÄTg (Step 9a)
79 = 1.57
(c) Find Factor ITD / ÄTg from I.T.D. factor Chart Fig 4B Page 6 using factor Äg above of 1.57. Factor ITD / ÄT = 2.0.
(d) Initial temperature between entering supply air and hot glycol (I.T .D.f) =
ITDf / ÄTg Factor x ÄTg (Step 9a)
= 2.0 x 79 °F
= 158 °F
(e) Hot Glycol Temperature = ITDf + Entering Supply Air Temperature °F
= 158 °F + 0 °F = 158 °F

TEMPERATURE AND ALTITUDE CONVERSION FACTORS

TABLE 1
The exhaust air coil glycol pressure drop is
10.75 x 2.93 = 31.5 ft. of water.
The supply air coil glycol pressure drop is
10.75 x 2.31 = 24.8 ft. of water.
(b) Air side Pressure Drop: Fig. 3, Page 5 indicates the air side pressure drop for an 8 row coil, 12 FPI at 400 F.P.M. face velocity is .49 inches W.G.
g
CONCLUSION
The following are the final coil selections:
Exhaust Air Coil: 1 - 8 row, 12 FPI, 45” x 120”
Fluid pressure drop -31.5 ft. of water Air side pressure drop .49” W.G.
Supply Air Coil: 1 - 8 row, 12 FPI, 45” x 90”
Fluid pressure drop - 24.8 ft. of water Air side pressure drop - .49” W.G.
Required Glycol Flow Rate: 45 U.S.G.P.M. of 50% Glycol solution. (By wt.)
RIA )TEEF(EDUTITLA
F°PMET000010002000300040005000600070008
02-
0
02 04 06 07 08
001 021 041 061 002 052
02.161.121.180.140.100.179.39.98.
51.101.180.120.199.59.29.88.58.
11.160.120.189.59.29.88.58.28.
60.120.189.49.19.88.48.18.87.
20.189.49.19.88.58.18.97.67.
00.169.39.98.68.38.08.77.47.
89.49.19.88.48
49.19.88.48.18.87.57.27.07.
29.88.58.18.87.67.27.07.76.
98.58.28.97.67.37.07.86.56.
58.28.97.67.47.07.86.56.36.
8.77.57.27.96.76.46.26.06.
0
57.27.96.76.56.26.06.85.65.
.18.87.57.27.
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