cw
ASR
ncfTmTSR
<5cJ«3RA70R
PlPtNS rOR MACHINE SiZES 16>® 077 THRO 124,
OR TWO St^íGt£-£^íO MACHINES fN PARAiXEL.
“Acid for 3-way vaive usaae. Pipe MC port (when 3-way valve
useO) to generator irvieris).
Fig. 6 — Suggested Piping For Hot Water Machines
Using Supply Hot Water 300 F or Below
P(PiN<3 FOR MftCHiNE SIZES 077 THRU t24
OR TWO SiNGL£-EN0 MACHINES iNRARALLEL
Fig. 7 — Suggested Piping For Hot Water Machines
Using Supply Hot Water Above 300 F
A three-way valve is recommended to ensure a
constant system flow of hot water supply re
gardless of load. A two-way valve is suitable when
throttling of supply hot water at partial load does
not adversely affect the boiler or primary circu
lating pump.
For Water Temperature Above 300 F —
gives suggested hot water piping when
Piping
Fig. 7
supply High-Temperature Hot Water (HTHW) is
above 300 F. The three-way valve — CVl, diverts
HTHW and allows cooler recirculated hot water to
maintain design hot water temperature (300 F
max).
Machine capacity is controlled by regulating the
flow of hot water thru the generator. As machine
load decreases, the chilled water controller senses
the lower chilled water temperature and acts upon
the three-way diverting valve(s) CV2
(CV2 + CV3) to reduce the supply of hot water
to the generator. The recirculating pump, however,
is actually pumping a constant gpm.
The sensor for CVl should be located, if
possible, on the discharge side of the recirculating
pump. The recirculating pump should be sized for
design hot water at a head equal to the pressure
drop through the generator and recirculating loop
piping.
An alarm should be used to warn of excessive
entering hot water temperatures. Excessive tem
peratures could develop if control valve calibration
were lost.
RECIRCULATING WATER CALCULATIONS -
Assume for example purposes;
Available supply hot water temp = 400 F
Design quantity of hot water needed = 243 gpm
Design entering hot water temp = 300 F
Design leaving hot water temp = 229 F
1. Determine the design hot water temperature
drop (ATi) thru the machine.
AT 1 = ent hot water (F) — Ivg hot water (F)
- 300 F - 229 F
= 71 F
2. Determine the temperature drop of 400 F
water (AT2) thru the machine.
AT2 = supply hot water (F) — Ivg hot water (F)
- 400 F^ 229 F
= 171 F
3. Determine the amount (gpm) of 400 F water
required.
Gpm of 400 F water
gpm of 300 F water
ATI
AT2
243 X-
71
171
= 101 gpm
Determine the amount (gpm) of recirculated
229 F water required to meet design quantity
of water needed:
Gpm of 229 F water - gpm of 300 F water
— gpm of 400 F water
= 243 - 101
- 142 gpm
