b 2 b may 2010 solutions

2Back BasicsBack BasicsMay 2010

SolutionBased on Cx-3 ATC/FPT software

TAB Existing AHU-1Measurement

PointCriteria On 24/7 Max Cool-

ingOn 24/7 Min Cooling On 24/7 Max Heat-

ingTAB Tester Questions

Design Actual Design Actual Design Actual

1Mixed air plenum

FlowStatic pressureVelocity

7,000 cfm-0.25 in. sp500 fpm

6,300 cfm-0.35 in. sp450 fpm

A. OK per basis of designB. OA damper D-1 open 100%C. OA damper D-1 closed creating excess static

pressure drop via excess return air (RA) -ANSWER

2After filter and before supply air fan


7,000 cfm-0.5 in. sp500 fpm

6,300 cfm-0.45 in. sp450 fpm

A. OK per basis of designB. Filter pressure drop excessive. Issue PM work-

order to replace filtersC. Filter pressure drop OK at reduced total cfm

-ANSWER

3After fan and before cooling coil


7,000 cfm+1.50 in. sp1,200 fpm

6,300 cfm+1.65 in. sp1,080 fpm

A. OK per basis of designB. OK based on reduced total supply air -ANSWERC. Supply fan needs to be re-sheaved to increase cfm

4After cooling coil and before reheat coil


7,000 cfm+0.50 in. sp400 fpm

6,300 cfm+0.50 in. sp360 fpm

A. OK per basis of designB. OK based on reduced total supply air -ANSWERC. Coil pressure drop excessive. Issue PM workorder

to clean coil

5After reheat coil


7,000 cfm+0.30 in. sp600 fpm

6,300 cfm+0.35 in. sp540 fpm

A. OK per basis of designB. OK based on reduced total supply air -ANSWERC. Coil pressure drop excessive. Issue PM workorder

to clean coil

63/4 Downstream In supply air duct


7,000 cfm-0.20 in. sp1100 fpm

6,300 cfm-0.20 in. sp990 fpm

A. OK per basis of designB. OK based on reduced total supply air -ANSWERC. Duct static pressure drop is excessive - Issue PM

workorder to clean ductwork

7CHWR downstreamof three-way V-1 valve

FlowHeadTemperature

48 gpm30 ft54˚F

48 gpm45 ft44˚F

A. OK per basis of designB. Excessive pump head from coilC. Coil is piped backwards -ANSWER

8CHWS upstream of three-way V-1 valve

FlowHeadTemperature

48 gpm45 ft44˚F

48 gpm30 ft54˚F

A. OK per basis of designB. Inadequate pump head to the coilC. Coil is piped backwards -ANSWER

9HWR downstream of three-way V-2 valve

FlowHeadTemperature

34 gpm30 ft180˚F

0 gpm35 ft190˚F

A. OK per basis of designB. Valve to reheat coil is closed per design sequence

-ANSWERC. Coil is piped backwards

b 2 b may 2010 solutions

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