ASHRAE Journal - August 2019 - 40

TECHNICAL FEATURE

40

ASHRAE JOURNAL

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Operational Cost Savings (%)

Operating Cost Per Year (USD)

Lifetime Cost Savings (%)

Lifetime Cost Over 15 Years (USD)

leaving the recovery chiller ranging from 104°F (40°C)
TABLE 1 Cost considered in the study.
to 140°F (60°C).
COMPONENT
UNIT
INVESTMENT COSTS
Figure 17 shows, respectively, the operating cost and
Chiller Only
USD/kW
200
operational cost savings function of recovery chiller
Recovery Chiller*
USD/kW
300
capacity and leaving hot water temperature. It shows
Boiler
USD/kW
115
clearly the decrease in energy cost (LPG + electricity)
COMPONENT
UNIT ANNUAL MAINTENANCE COSTS
where the savings can reach 17% for 104°F (40°C) leavAll Above-Listed Units
% CAPEX
4%
ing hot water temperature. At 140°F (60°C) leaving hot
ENERGY COST
UNIT
CURRENT PRICE
water temperature, the savings in energy cost are more
14
LPG
USD/kWh
0.025
than 26%.
15
USD/kWh
0.033
Electricity
Increasing the recovery chiller capacity has an impact
*Recovery chiller + additional auxiliaries
also, as more heat and cold can be produced by the
latter. However, the savings in
FIGURE 17 Operating cost and operational cost savings function of recovery chiller capacity and leaving hot water
operational cost (OPEX) reaches a
temperature.
30
450,000
saturation threshold due to the fact
that heat produced by the boiler is
25
420,000
always needed for the 176°F (80°C)
hot water production.
20
390,000
Figure 18 shows, respectively, the
15
360,000
lifetime cost and lifetime cost savings function of recovery chiller
10
330,000
capacity and leaving hot water
temperature. It shows clearly the
5
300,000
decrease in lifetime cost (CAPEX
0
270,000
+ OPEX + LPG + electricity) where
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
the savings can reach 13% for 104°F
Recovery Chiller Heat Capacity (kW)
(40°C) leaving hot water temperaHot Water RC 40
Hot Water RC 45
Hot Water RC 50
ture. At 140°F (60°C) leaving hot
Hot Water RC 55
Hot Water RC 60
water temperature, the savings in
lifetime cost are almost 20%.
Increasing the recovery chiller
FIGURE 18 LCCA over 15 years function of recovery chiller capacity and leaving hot water temperature.
capacity has an impact also as
9,250,000
22
more heat and cold can be pro9,000,000
20
8,750,000
duced by the latter. However, the
18
8,500,000
16
savings in running cost reach a
8,250,000
14
saturation threshold due to the
8,000,000
12
fact that heat produced by the
7,750,000
10
boiler is always needed for the
7,500,000
8
176°F (80°C) hot water production.
7,250,000
6
The peak savings is reached in the
7,000,000
4
range of 800 kW to 1,000 kW (228
6,750,000
2
ton to 284 ton) chiller heat capac6,500,000
0
0
200
400
600
800 1,000 1,200 1,400 1,600 1,800 2,000
ity. For larger capacities, lifetime
cost savings start to decrease due
Recovery Chiller Heat Capacity (kW)
to the large increase in capital
Hot Water RC 40
Hot Water RC 45
Hot Water RC 50
expenditure (CAPEX) and less savHot Water RC 55
Hot Water RC 60
ings in running cost.
A U G U S T 2 0 19
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ASHRAE Journal - August 2019

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