In HVAC plant simulation software, a pump model is required to carry out pressure based simulation, which will govern flow rate in system and predict accurate power consumption. To implement a pump model in EnergyPlus, which will predict pump performance with varied pump parameters such as rotational speed and pump diameter pump performance models and non-dimensional model was studied. Their applicability and accuracy was checked experimentally and with manufacturer's data. Using the pump performance prediction model effect of pump parameters on its performance was observed. Also applicability of affinity laws to predict pump power savings was studied. It was observed that performance prediction models calculate the pump performance with sufficient accuracy but are not suitable to implement in energy simulation programs when the pump has been specified and pump curves are available. These models can be used to determine the effect of each individual parameter on the performance curve. When the size of the pump is unknown, in a hydronic system sizing calculation, these models can be used to predict the inlet and outlet diameters of the pump impeller, assisting the designer in sizing the pump for the system. Due to simplicity, less number of input requirements and accuracy a non-dimensional model was found to be suitable for energy simulation purpose. But, when checked with manufacturer's data it was observed that these non-dimensional models cannot be used directly for variation in impeller diameter. A modified non-dimensional model was suggested which not only satisfied the pump affinity laws but also gave better results as compared to earlier non-dimensional model suggested by Clark (1985). This modified non-dimensional model with VFD control is implemented in EnergyPlus. It was also found that pump affinity laws can be used for predicting power savings only if there is linear relationship between input and output power of the pumping system. The ranges for applicability of the pump affinity laws to predict power savings were found using standard electrical motor efficiency curves.

1. DEVELOPMENT, IMPLEMENTATION AND
VALIDATIONOF A NON-DIMENSIONAL
PUMP MODEL IN ENERGYPLUS
Kaustubh Phalak
Advisor: Dr. Daniel Fisher
Committee members
Dr. Jeffery Spitler
Dr. Lorenzo Cremaschi
Mechanical and Aerospace Engineering Department
Oklahoma State University, Stillwater, 74078

2. PRESENTATION ORGANIZATION
 Theoretical Study
 Performance prediction models
 Non-dimensional model
 Experimental Validation
 Implementation in EnergyPlus
2

3. PERFORMANCE PREDICTION MODELS
 Study effect of pump parameters on pump
performance
 Effective pump head = Hth - hlosses
3
Hth= f(D2,
N, W, Q,
β2)
hlosses= g(D1, D2, N, W, Q, Z, β2 ,
β2)
H

4. RESULTS OF PERFORMANCE PREDICTION
MODELS
 Results of Tuzson
and Spannhake
model match with
manufacturers data
 Friction losses are
minor losses (max
10% of theoretical
head)
4

5. RESULTS OF PERFORMANCE PREDICTION
MODELS
 Calibration of models
 Effect of Impeller
diameter
 Effect of Impeller
inlet diameter
 Limitations
5

6. RESULTS OF PERFORMANCE PREDICTION
MODELS: SIZING
 Observation: shutoff head is 30% of the
calculated theoretical head
 Observation: design flow rate is proportional
to square of impeller inlet diameter
6
 0.3
p
2
1
×
1.524
d2
n

2
BEP
1
dn
qk
0.002=d

7. ND
m
= 31



NON-DIMENSIONAL Π-PRODUCTS
 HVAC Toolkit
 Simplified model, fewer
inputs
 Inconsistent with the
affinity laws
 Effect of rotational
speed on π-products
 Effect of impeller
diameter on π-products
 Geometrical similarity
7

8. MODIFIED NON-DIMENSIONAL MODEL
8
NDA
m
=
ND
m
31



 
 D3 factor replaced by
AD, to be consistent
with the affinity laws
 Effect of diameter is not
completely eliminated
 Maximum deviation up
to -30% is observed
 Better results obtained
with modified model

9. EXPERIMENTAL VALIDATION
 Validation of pump
model and the affinity
laws
 Validation with
respect to rotational
speed
 Verification of power
savings: 50%
reduction in rotational
speed →88%
reduction in power 9

10. EXPERIMENTAL RESULTS
 Non-dimensional
pump curve
 Flow rate and ф vs.
rotational speed
 Pressure rise and ψ
vs. rotational speed
 Output power vs.
rotational speed
10

11. EXPERIMENTAL RESULTS: POWER SAVINGS
 Power savings: dependent
on pump input power
 Large deviation in actual
and estimated input power
 Applicability of affinity
laws: i/p power directly
proportional to o/p power
 Component efficiencies
not constant
 E. motor efficiency curves
highly steep w.r.t.
rotational speeds
11
hp Motor η Threshold
% Allowable speed
reduction
0-1 65 13.4
1.5-5 45 23.4
5.5-15 30 33.1
15-25 25 37.0
30-60 18 43.5
75-100 10 53.6

12. ENERGYPLUS: EARLIER PUMP MODELS
 Constant speed pumps: nominal flow rate
and rated power for all the systems
irrespective of pumping load
 Variable speed pumps: flow between the
min-max flow range and power from PLR
curve
 Plant Pressure Systems
12

13. ENERGYPLUS: FLOW RESOLUTION
 Newton-Raphson or a successive
substitution method investigated
 Newton-Raphson: presence of maxima or
minima of the equation leads to divergence
 Successive substitution: calculating
sequence and information flow decides
convergence
 Reversing the sequence is not simple if
divergence is detected
13

14. ENERGYPLUS: MODIFIED SUCCESSIVE
SUBSTITUTION
 Slopes at operating
point decides
converging flow
sequence
 Inclusion of damping
factor
 Iterations are
reduced
 Divergence is
avoided 14

15. VFD CONTROL
 Manual control:
Pump curve is
scaled according to
RPM schedule
 Pressure set-point
control
15
0
70
140
210
0 75 150
Head
Flow
VFD pressure
controlrange
maxRPM
SystemCurve
A
B
C
D
minRPM
E F

16. ENERGYPLUS: RESULTS & FUTURE WORK
 Flow resolution:
convergence is
achieved for various
systems
 Power consumed
dependent on
resolved flow rate
 VFD controls tested
 Efficiency curves
16
Mode
no.
Type of operation Mass flow rate
Energy
(kWhr)
1
No pressure
simulation
6.28 (Rated flow
rate )
192
2
Pressure simulation
constant speed pump
4.63 133.5
3 VFD (RPM schedule) 0.51 - 4.22 22.7
4
VFD (Pressure set-
point control)
0.33 - 3.98 18.9

17. 17
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