hvac myths and realities - ashrae® illinois...
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![Page 1: HVAC Myths and Realities - ASHRAE® Illinois Chapterillinoisashrae.org/images/meeting/042917/2016_17_Documents/hvac...HVAC Myths and Realities ... • 55°F supply air temperature](https://reader036.vdocuments.mx/reader036/viewer/2022070608/5ab0d1327f8b9a00728b8668/html5/thumbnails/1.jpg)
HVAC Myths and Realities Trane Engineers Newsletter Live Series
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AGENDA
• Low delta T is unavoidable • 55°F supply air temperature is adequate for today’s loads • ASHRAE Standard 15 has to be updated before new refrigerants
can be used • Single-zone VAV units do not need hot gas reheat • VFDs and affinity laws • Small changes in pressure can have a huge impact on airflow for
flat fan curves and may cause the system to surge • New chilled-water systems need to be variable-primary flow • System airflow issues are the fans fault • Claims to energy savings
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Low delta T is unavoidable.
Myth Number 1
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• Tons= (∆T ×GPM)/24 Solving for gpm…
• GPM= (Tons ×24) /∆T Pumping power…
• Frictional Head ∝ Flow
2
• Water HP (bhp)= (GPM × head (ft))/3960
• Water HP ∝ Flow 3 ∝ Delta T 3
Transport Energy is low delta T unavoidable?
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v • AHRI Certified Coil • Air Flow (VAV)
unloading
Coil Delta T is low delta T unavoidable?
2015 Engineer’s Newsletter Live Coil Selection and Optimization
ASHRAE 90.1-2016 6.5.4.7 Chilled-Water Coil Selection Chilled-water cooling coils shall be selected to provide a 15°F or higher temperature difference between leaving and entering water temperatures and a minimum of 57°F leaving water temperature at design conditions.
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1. 3-way control valves
Reason 1: 3-Way Control Valves undesirable mixing in variable flow systems
CHWS 42°F
Bypass 42°F
CHWR 50.5°F
Coil LVG 59°F
50% Coil Load
CHWR = [(42° x 50) + (59° x 50)] / 100 = 50.5°
• Eliminate them!
Coil Delta T = 17°F
System Delta T = 8.5°F
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0
5
10
15
20
25
50 52 54 56 58 60
CHW
Del
ta T
leaving air setpoint
1. 3-way control valves 2. Control setpoint depression
Reason 2: Supply Air Setpoint Depression overdriving coil capacity
• Avoid, limit and return
55° LAT = 16° DT 52° LAT = 11° DT 50° LAT = 8.5° DT
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0
5
10
15
20
25
35 40 45 50
CH
W D
elta
T
entering CHW temperature
1. 3-way control valves 2. LAT setpoint depression 3. Warmer chilled water
Reason 3: Warmer Chilled Water Supply reduced heat transfer driving force “LMTD”
• Chilled water reset only at part load
42° CHWS = 16° DT 47° CHWS = 7.5° DT 50° CHWS = 5° DT
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1. 3-way control valves 2. LAT setpoint depression 3. Warmer chilled water 4. Deficient control valves
Reason 4: Deficient Control Valves poor flow control at full and part loads
Control Valve Issues 1. Improperly
Selected / Oversized 2. Worn-out 3. Unstable control 4. $29.95 (cheap) 5. 3-way valves
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1. 3-way control valves 2. LAT setpoint depression 3. Warmer chilled water 4. Deficient control valves
Reason 4: Deficient Control Valves poor flow control 8th floor
control point 20 ft pd
2nd floor pressure 90 ft pd
• Specify quality valves specific to use
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1. 3-way control valves 2. LAT setpoint depression 3. Warmer chilled water 4. Deficient control valves
Reason 4: Deficient Control Valves poor flow control
Pressure independent valves? (PIV) 1. Mechanical 2. Electronic
Pressure independent valves • Not required • May be beneficial
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1. 3-way control valves 2. LAT setpoint depression 3. Warmer chilled water 4. Deficient control valves 5. Tertiary pumping /
bridge tender circuits
Reason 5: Tertiary Pumping undesirable mixing is hard to prevent
CHWS
CHWR
“Bypass” Valve
DP
• Don’t mix to the return – simply pressure boost
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1. AHRI certified coil selections 2. AHU set point limits 3. Chilled water reset only at
part load 4. Properly selected /
high quality valves 5. Pressure boosting –
no tertiary “mixing”
Design Delta T and Greater is Achievable
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Low Delta T is unavoidable.
Myth Number 1
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55°F supply air temperature is adequate for today’s loads.
Myth Number 2
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full load OA 96°F DB,
76°F WB
MA 80°F DB
RA 74°F DB, 52% RH
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
full load
OA
MA RA SA
SA 55°F DB (1,500 cfm)
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full load OA 96°F DB,
76°F WB
MA 86°F DB
RA 74°F DB, 57% RH
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
full load
OA
MA RA SA
SA 55°F DB (800 cfm)
RA'
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full load OA 96°F DB,
76°F WB
MA 89°F DB
RA 74°F DB, 52% RH
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
full load
OA
MA RA SA
SA 51°F DB (630 cfm)
SA'
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Improving Dehumidification • Cool and reheat • Face-and-bypass dampers • Reduce airflow • Dual paths • Desiccants
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full load OA 96°F DB,
76°F WB
MA 86°F DB
RA 74°F DB, 52% RH
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
full load
OA
MA RA SA
SA 52 (55)°F DB (800 cfm)
CA SA'
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Type III Series Desiccant (CDQ)
MA
SA
55°F DB 64% RH 42 gr/lb (43°F DP)
50°F DB 97% RH 52 gr/lb
MA'
80°F DB 50% RH 77 gr/lb (60°F DP) (10,000 cfm)
75°F DB 67% RH 87 gr/lb (64°F DP)
8-12 rph
CA C
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full load OA 96°F DB,
76°F WB
MA 81°F DB
RA 74°F DB, 52% RH
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
full load
OA
MA RA SA
SA 63°F DB (1,350 cfm)
CA
MA'
SA'
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55°F supply air temperature is adequate for today’s loads.
Myth Number 2
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Single-zone VAV units do not need hot gas reheat.
Myth Number 3
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outdoor condition
sensible load
latent load
space SHR
supply airflow
outdoor airflow
space temp
supply air temp
peak DB
96°F DB, 76°F WB
29,750 Btu/h
5,250 Btu/h
0.85
1,500 cfm
450 cfm
74°F
55.7°F
Classroom Example basic CV system
29,750 Btu/h 1.085 × (74°F – Tsupply)
1,500 cfm =
Jacksonville, Florida
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180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
OA
MA
RA
SA
Jacksonville, FL
84°F DBT 76°F DPT (450 cfm)
77°F DBT
63°F DBT (1500 cfm)
part load CV
96°F DBT 68°F DPT (450 cfm)
81°F DBT
74°F DBT 52% RH
55°F DBT (1500 cfm) (4.8 tons)
full load CV
peak DPT OA
MA SA peak DBT OA
MA RA SA
RA
74°F DBT 67% RH
Example: K-12 Classroom
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OA
MA
RA
SA
84°F DBT 76°F DPT (450 cfm)
77°F DBT
63°F DBT (1500 cfm) (3.7 tons)
96°F DBT 68°F DPT (450 cfm)
81°F DBT
74°F DBT 52% RH
55°F DBT (1500 cfm) (4.8 tons)
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
peak DPT OA
MA SA
MA RA SA
RA
74°F DBT 67% RH
part load CV
full load CV
Jacksonville, FL
peak DBT OA
Example: K-12 Classroom
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peak DPT day zone humidity, %RH 67% cooling load, tons 3.7 fan airflow, cfm 1500
mild/rainy day zone humidity, %RH 73% cooling load, tons 1.6 fan airflow, cfm 1500
constant-speed fan
Example: K-12 Classroom
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Hot Gas Reheat packaged DX units
condenser
MA
reheat valve
CA
reheat coil
evaporator
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constant-speed fan
constant-speed fan with hot gas reheat
60% 2.4
1500
55% 3.7
1500
Space humidity is maintained
Example: K-12 Classroom
peak DPT day zone humidity, %RH 67% cooling load, tons 3.7 fan airflow, cfm 1500
mild/rainy day zone humidity, %RH 73% cooling load, tons 1.6 fan airflow, cfm 1500 compressor energy
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SA OA
1500 cfm
EA
Improved Part-Load Dehumidification
RA
450 cfm
55°F 96°F DBT 68°F DPT
1050 cfm zone 74°F
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OA
MA
RA
SA
84°F DBT 76°F DPT (450 cfm)
77°F DBT
63°F DBT (1500 cfm) (3.7 tons)
96°F DBT 68°F DPT (450 cfm)
81°F DBT
74°F DBT 52% RH
55°F DBT (1500 cfm) (4.8 tons)
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
peak DPT OA
MA SA
MA
RA SA
RA
74°F DBT 67% RH
part load CV
full load CV
84°F DBT 76°F DPT (450 cfm)
79°F DBT
55°F DBT (900 cfm) (4.0 tons)
74°F DBT 57% RH
part load SZVAV
Jacksonville, FL
Example: K-12 Classroom
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peak DPT day zone humidity, %RH 67% cooling load, tons 3.7 fan airflow, cfm 1500
mild/rainy day zone humidity, %RH 73% cooling load, tons 1.6 fan airflow, cfm 1500
variable-speed fan
constant-speed fan
constant-speed fan with hot gas reheat
60% 2.4
1500
55% 3.7
1500
57% 4.0 900
60% 1.9 750
Example: K-12 Classroom
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SZVAV Dehumidification Performance
• VAV may be enough • Consider hot gas reheat for:
§ Even lower space humidity levels § Widely varying loads § Oversized units
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180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60
OA
MA
RA
SA
96°F DBT 68°F DPT (450 cfm)
80°F DBT
58°F DBT (1750 cfm)
96°F DBT 68°F DPT (450 cfm)
81°F DBT
74°F DBT 52% RH
55°F DBT (1500 cfm)
peak DPT OA
MA MA
74°F DBT 56% RH
Oversized SZVAV
full load SZVAV
84°F DBT 76°F DPT (450 cfm)
78°F DBT
58°F DBT (1050 cfm)
74°F DBT 59% RH
part load SZVAV
Jacksonville, FL
MA RA SA
peak DBT OA
SA SA RA RA
Example: K-12 Classroom
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Avoid Oversizing!
• Oversizing supply airflow leads to: § Warmer supply-air temperature § Less dehumidification
(in non-arid climates) § Elevated indoor humidity
• Examples include: § Auditoriums § Gymnasiums § Church sanctuaries § Etc.
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Humidity Control with SZVAV
• Avoid oversizing equipment • Verify proper fan speed and discharge air temperature
setpoints • Equip the unit with hot gas reheat,
if necessary
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Single-zone VAV units do not need hot gas reheat
Myth Number 4
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Slap on a VFD and you are entitled to get full advantage of the affinity laws.
Myth Number 4
= Speed3 Savings
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Background: 1. Fans, pump impellers and other “dynamic compression”
devices. 2. Application limited to systems with only frictional flow losses. 3. Ignoring changes in device efficiency at different conditions.
If and only if the above are true then: 1. Pressure varies proportionally to the square of the impeller
speed. 2. Flow produced varies proportionally to the impeller speed. 3. Power (BHP) required varies in a cubic proportion to the
impeller speed.
The Affinity Laws dynamic compression fans/impellers
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The Affinity Laws – Graphically dynamic compression fans/impellers Device performance in frictional pressure loss systems • Pressure is proportional to the
speed squared • Flow is proportional to the
speed • Power is proportional to the
speed cubed
75
50
25
0
100
0 25 50 75 100 flo
w/p
ress
ure/
pow
er (%
) speed (%)
pressure flow power
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Systems and the Affinity Laws compliant systems
Systems that comply • Cooling towers • Single zone VAV air systems.
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Cooling Tower Fans affinity laws
Cooling Tower
85°F 100°F
Cooling Tower
60 HZ OFF
15 kW
75
50
25
0
100
0 25 50 75 100 sp
eed/
pres
sure
/pow
er (%
) flow (%)
speed pressure power
100% flow 100% pressure 100% power
P
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Cooling Tower Fans affinity laws
Cooling Tower
85°F 92.5°F
Cooling Tower
60 HZ OFF
1.88 kW
For “Free Discharge” Fans W2 = W1 x (S2 / S1)3
W2 = 15 kW x (30 / 60)3
W2 = 1.88 kW 75
50
25
0
100
0 25 50 75 100 sp
eed/
pres
sure
/pow
er (%
) flow (%)
speed pressure power
P
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Systems and the Affinity Laws non-compliant systems
Systems that don’t comply: • Chilled water • Hot water • MultiZone VAV • Condenser water • HVAC cooling units • HVAC heating units (HP)
Non-compliant characteristics:
Control valves and setpoints
Fixed lift Refrigeration lift / heat exchangers / minimum flows
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75
50
25
0
100
spee
d/pr
essu
re/p
ower
(%)
VPF Chilled Water Systems systems and the affinity laws
0 25 50 75 100 flow (%)
speed pressure power
Non-compliance factors • Pump minimum speed
limits
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Pump Minimum Speed Impact VPF chilled-water systems
0 25 50 75 100 flow (%)
pump min speed
75
50
25
0
100
spee
d/pr
essu
re/p
ower
(%)
Non-compliance factors • Pump minimum speed
limits • 33% minimum speed
pressure power
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Differential Pressure Control Impact VPF chilled-water systems
0 25 50 75 100 flow (%)
DP pressure setpoint
75
50
25
0
100
spee
d/pr
essu
re/p
ower
(%)
Non-compliance factors • Pump minimum speed
limits • A fixed pressure control
setpoint • 20 ft. setpoint • 80 ft. frictional loss
speed power
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Heat Exchanger Minimum Flow Impact VPF chilled-water systems
0 25 50 75 100 flow (%)
HX min flow
75
50
25
0
100
spee
d/pr
essu
re/p
ower
(%)
Non-compliance factors • Pump minimum speed
limits • A fixed pressure control
setpoint • Heat exchanger minimum
flow limits • 50% minimum flow
pressure power
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Combined Limit Power Impact VPF chilled-water systems
Non-compliance factors • Pump minimum speed
limits • A fixed pressure control
setpoint • Heat exchanger minimum
flow limits 0 25 50 75 100
75
50
25
0
100
spee
d/pr
essu
re/p
ower
(%)
flow (%)
Pump min speed HX min flow DP setpoint
affinity power
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Non-compliance factors • Pump minimum speed
limits • A fixed pressure control
setpoint • Heat exchanger minimum
flow limit – 70%
High HX Minimum Flow Impact VPF chilled-water systems
0 25 50 75 100 flow (%)
HX min flow
75
50
25
0
100
spee
d/pr
essu
re/p
ower
(%)
pressure power
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Systems that comply • Cooling towers • Single zone VAV HVAC
systems.
Systems that don’t comply • Chilled water • Hot water • Condenser water • Multi-zone VAV • HVAC cooling units • HVAC heating units (HP)
Slap on a VFD and you are entitled to get full advantage of the affinity laws.
Myth Number 4
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Small changes in pressure can have a huge impact on airflow for flat fan curves and may cause a fan system to surge.
Myth Number 5
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1100 RPM
900 RPM
700 RPM
500 RPM
50% WOCFM 60%
70%
80%
90%
Forward Curved (FC) Fan St
atic
pre
ssur
e in
ches
w.g
.
CFM in 1000s
peak pressure
Small Changes in Pressure
“Do not select” region
Far from peak – some may select here
6
5
4
3
2
1
0 0 4 8 12 16 20
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Fan Performance Test
7
6
5
4
3
2
1
0 0 2500 5000 7500 10000 12500 15000 17500 20000 22500
airflow (cfm)
tota
l sta
tic p
ress
ure
(in H
2O)
less restricted
wide open
blocked off
restricted
14
12
10
8
6
4
2
0
Bra
ke h
orse
pow
er (b
hp)
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1100 RPM
900 RPM
700 RPM
500 RPM
50% WOCFM 60%
70%
80%
90%
Forward Curved (FC) Fan st
atic
pre
ssur
e in
ches
w.g
.
CFM in 1000s
Pressure = f(Airflow)
6
5
4
3
2
1
0 0 4 8 12 16 20
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1100 RPM
900 RPM
700 RPM
500 RPM
50% WOCFM 60%
70%
80%
90%
stat
ic p
ress
ure
inch
es w
.g.
CFM in 1000s
Two Different Systems
actual system Design system
6
5
4
3
2
1
0 0 4 8 12 16 20
Forward Curved (FC) Fan
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stat
ic p
ress
ure
inch
es w
.g.
CFM
Fan
Is dependent on the
System
System
Is dependent on the
Fan
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System Change: Steep Fan Curve
60 % WO
70 % WO
80 % WO
90 % WO
50 % WO 45 % WO
1000 RPM
700 RPM
1300 RPM
1500 RPM
2000
RP
M
1500
RP
M
1000
RP
M
1750
RP
M
500
RP
M
300
RP
M
200
RP
M
150
RP
M
100
RP
M
airflow (cfm)
tota
l sta
tic p
ress
ure
(in H
2O)
8
7
6
5
4
3
2
1
0 0 5000 10000 15000 20000 25000
25-inch steep fan curve
0.5 change 14,500 cfm
(vs. 15,000 cfm) 3.3% loss
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50 % WO
25 % WO
60 % WO
70 % WO
80 % WO
90 % WO
300 RPM
400 RPM
500 RPM
600 RPM
700 RPM
800 RPM
2000
bhp
1500
bhp
750
bhp
1000
bhp
500
bhp
5000 10000 15000 20000 25000 30000 35000 40000 45000 0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
tota
l sta
tic p
ress
ure
(in H
2O)
airflow (cfm)
0.5 change
System Change: Flat Fan Curve 25-inch flat fan curve
14,500 cfm (vs. 15,000 cfm)
6.7% loss
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Small changes in pressure can have a huge impact on airflow for flat fan curves and may cause a fan system to surge.
Myth Number 6
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A chilled water system needs to be variable primary flow to be efficient.
Myth Number 6
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Variable Primary Flow (VPF) Savings
• First cost: 4-8% • Annual energy: 3-8% • Life-cycle cost: 3-5%
Compared VPF and Primary-Secondary
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• Install pump VSD • Use VSD to set design flow rate • Open balancing valve • Employ chilled water reset
Low Pump Power
If system is constant flow – reduce design flow rate further
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Design Flow ~ Minimum Flow
• Chilled water ∆Ts • ASHRAE GreenGuide (16-18°F ∆T) • 90.1-2016 Section 6.5.4.7
• Coil shall be selected to “…provide 15°F or higher temperature difference between leaving and entering temperatures.”
• Chillers with limited evaporator choices
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Single chiller • Turndown > 1.3
Two chillers • Turndown > 1.5 • Consider piping the
chillers in series
Design Flow ~ Minimum Flow Flow turndown = Design flow / Minimum flow
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Convert to VPF • If entire plant is being
re-piped anyway • Additional capacity is needed • Install chiller where primary
pumps used to be
Change to Variable-Primary/Variable-Secondary • Cooling capacity is adequate • Piping changes are minimal
Conversion from Primary-Secondary
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Convert to Variable Primary/Variable Secondary
Placeholder for Manifolded P-S System picture (Beth to supply)
VFDs DP
DP
ΔT = 1 or 2 ºF
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• Doesn’t understand the plant • Wants to manually control
Plant Operator
VPF
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A chilled water system needs to be variable primary flow to be efficient.
Myth Number 7
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Fans often don’t deliver the airflow they are supposed to—and it’s the fan’s fault.
Myth Number 7
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Test chamber
ANSI/ASHRAE 51 (AMCA 210-07) Figure 12: “Outlet Chamber Setup-Multiple Nozzles in Chamber”
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System Effect: Developing a Uniform Velocity Profile
uniform velocity profile
fan
Not enough space to fully develop
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OA
Free and Abrupt Discharge “Hidden” loss as high as 1.0 inches w.g.
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AMCA Publication 201, Fans and Systems
Prediction of common System Effect Factors
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Common System Effects
• Open discharge, elbow, branch, turning vanes, or damper located too close to the fan outlet
• Elbow, turning vanes, air straightener, or other obstruction located too close to the fan inlet
• Pre-swirling the air prior to it entering the fan wheel
• Use of an inlet plenum or cabinet
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Flex Duct Problems
Good Bad
flex duct
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Common problems: • Unexpectedly high system pressures • Leaks • Fan installed or running backwards
Low Airflow Troubleshooting
Close-coupled fittings
From A Practical Guide to Noise and Vibration Control for HVAC Systems (M. Schaffer, 1991)
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Fan Rotation Forward-curved Backward-tended
Backward-inclined
Backward-curved
Airfoil
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Over-amping problems: • Bad component (motor or bearings) • Installation:
• Wheel-cone overlap • Belt tension, belt/shaft alignment
Low Airflow Troubleshooting
Wheel-cone overlap
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Uncommon problems: • Wrong fan installed • Cutoff issues (housed fans only) • Software/catalog error • Quantum mechanics & string theory
Low Airflow Troubleshooting
Fan cutoff (split in this case)
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Evaluating the right parameters: • Airflow • Pressure • Speed • Power
Things to watch out for: • VFD settings • Damper position (systems
with a return or exhaust fan) • Parameter measurement error
Field Measurements
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Parameter Measurement Error
Your duct system?
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Parameter Measurement Error AMCA 203 “Field Performance Measurement of Fan Systems”
http://www.amca.org/
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AMCA Fan Application Manual
Publication 201 “Fans and Systems” • Lists possible causes for low flow, including:
− Improper inlet duct design − Improper outlet duct design − Improper fan installation − Unexpected system resistance characteristics − Improper allowance for fan system effect − Dirty filters, ducts, coils − “Performance” determined using uncertain field
measurement techniques
• Includes much help for system effect corrections
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AMCA Fan Application Manual
Publication 202 “Troubleshooting” • Lists possible causes for low airflow, including:
− Improper fan installation or assembly − Damage in handling or transit − System design error − Deterioration of system − Faulty controls − Poor fan selection
• Includes detailed troubleshooting checklists
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Fans often don’t deliver the airflow they are supposed to—and it’s the fan’s fault.
Myth Number 8
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You can save (20, 30, 40, 50 80) percent….just by doing this…
Myth Number 8
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Savings Claims – 40 is the new 30!
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50 is the New 40
improved system efficiency of up to 54%
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And now from an online brochure…
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• Compared to what? What is the baseline? • What else changed? (particularly for retrofits).
Percent Savings: Questions to Ask
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• Compared to what? What is the baseline? • What else changed? (particularly for retrofits). • Is the comparison valid for
§ Your building? § Your application and load profile? § Your climate?
Percent Savings: Questions to Ask
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• Indirect evaporative cooling • Compared to compressor cooling • Dry climate • Water is available
78.5 Percent Claim
Does the solution meet my customers needs?
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• Make sure the baseline and comparison are valid for the specific project
• Perform an analysis on energy savings, energy cost savings, and ROI
• Help the client determine if the solution is in both their short-term and long-term interests
You can save (20, 30, 40, 50 80) percent….just by doing this…
Myth Number 8
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Anti-freeze doesn’t have much affect on chilled water systems.
Myth Number 9
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Example Fluid Properties and Impacts
Fluid Property Compared to Water
Impact Result
Viscosity Increases Pressure drop increases Pump power increases
Film heat transfer coefficient
Drops Heat transfer worsens More flow required
Specific heat Drops More flow required Pressure drop and pump power increase
Specific gravity Rises Less flow required Pressure drop and pump power increase
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Fluid Properties at 60°F
Property Water 25% EG 25% PG
Viscosity (lb/hr-ft) 2.68 5.25 6.49 Thermal conductivity (Btu/hr-ft-°F)
0.3445 0.2894 0.2773
Specific heat (Btu/lb-°F)
1.0016 0.9066 0.9410
Specific gravity 1.0000 1.0331 1.0216
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©ASHRAE, www.ashrae.org. (2016) ASHRAE Handbook – HVAC Systems and Equipment.
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Antifreeze Affect on the Coil
• “…heat transfer capability can change by 40% or more when antifreeze solutions are used…
• …consult the manufacturer’s rating data…in glycol systems.”
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Antifreeze Affect on the Chiller
17% Reduction
©ASHRAE, www.ashrae.org. (2016) ASHRAE Handbook – HVAC Systems and Equipment.
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Required Flow
Tons= 500 ×gpm × ∆T ×cp × /12,000
Tons(water)= gpm × ∆T /24
Tons(25% EG)= gpm × ∆T /25.5
Tons(25% PG)= gpm × ∆T /25
ɤ ( ῤ/ῤ𝑤 )
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Antifreeze Affect
• Water: gpm = 24 x tons x ΔT • 25% EG: gpm = 25.5 x tons x ΔT • 25% PG: gpm = 25 x tons x ΔT
More flow is required
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Affect of Antifreeze on Flow
• ΔP ∝ (Flow2 / Flow1)2
• Δ Pump Power ∝ (Flow2 / Flow1)3
Antifreeze Flow increase (%) Pressure drop increase (%)
Pump power increase (%)
25% EG 6.2 13 20
25% PG 4.2 8.5 13
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Affect of Antifreeze Viscosity
• Pressure drop increase 25% EG: 9%
25% PG: 17%
©ASHRAE, www.ashrae.org. (2016) ASHRAE Handbook – HVAC Systems and Equipment.
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Reality: Affects of Antifreeze
• Capacity − Coil − Chiller
• Pump − Flow − Pressure − Power
It’s all bad… except the system doesn’t freeze
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“…use the smallest possible concentration to produce the desired antifreeze properties.”
Guidance
©ASHRAE, www.ashrae.org. (2016) ASHRAE Handbook – HVAC Systems and Equipment.
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• Burst protection • Keep pipes from bursting • Crystal formation is ok • Use when equipment is not going to run in winter
• Freeze protection • Solution must remain 100% liquid • Necessary when equipment operates in freezing conditions
Freeze and Burst Protection
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Ethylene Glycol % Propylene Glycol %
Temperature (°F) Freeze Burst Freeze Burst
20 16.8 11.5 18 12
10 26.2 17.8 29 20
0 34.6 23.1 36 24
-10 40.9 27.3 42 28
-20 46.1 31.4 46 30
-30 50.3 31.4 50 33
-40 54.5 31.4 54 35
Freeze and Burst Protection
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Anti-freeze doesn’t have much affect on chilled water systems.
Myth Number 10