Retrotec USACE - Manual (Page 387)

Appendix J J11
J.9 AHU and Their Cooling Coils Retrofi t Strategies
8.1. The AHU should be confi gured in a blow-through rather than draw-
through confi guration. The fans should be upstream of the cooling
coils, blowing through them.
8.2. Provide cooling coils that meet the desired leaving air temperatures
with 50 °F entering chilled water temperature and as close to 70 °F
leaving chilled water temperature as possible.
8.3. The maximum cooling coil face velocity should be 350 fpm for blow-
through and 300 fpm for draw-through.
8.4. The desired fans are direct drive plug fans.
8.5. The cooling coils should be eight rows deep.
8.6. The cooling coils should have 12 fi ns/25.4mm (12 fi ns/in).
8.7. The maximum leaving air temperature should be 55 °F.
8.8 The minimum fi n thickness is 2 mm (0.008 in).
8.9. The minimum tube wall thickness is 0.71 mm (0.028 in).
8.10. The minimum tube diameter is 15.8mm (5/8 in).
8.11. The coils shall be equipped with individually replaceable return bends
of no less than 0.89 mm (0.035-in) thickness.
8.12. Hairpin return bends are not acceptable.
8.13. Stainless steel coil casings and intermediate tube supports must be
provided.
8.14. The maximum height between drain pans should be 0.6 m (24 in).
Provide coils that have drain pans that completely pass through the
cooling coil fi nned surface area.
8.15. The coil air pressure drop should be less than 0.8 in wc.
8.16 The coil water pressure drop should be less than 4.6 m (15 ft).
8.17 Provide low pressure drop (13.8 kPa (2 PSID) maximum) automatic
control valves for the cooling coil duty. Desired valves are pressure-
independent characterized port ball valves—Belimo or equivalent,
designed for outdoor duty. Provide with a sun/rain shield for the
actuators.
8.18 Insulation system should be vapor-tight and aluminum-skinned.