Design and Modeling of Combined Heat and
Power Systems for Sustainable Urban
Agriculture and Aquaculture
Team Members:
Ben Steffes
Dan Neumann
Brandon Jackson
Nate Weber
Chris Chapman
Faculty Advisor:
Dr. Chris Damm
Milwaukee School of Engineering
AQUAPONICS OVERVIEW
Borrowed from:
http://www.photosbysc.com/Aquaponics/Saras_Aquaponic_Blog/Entries/2008/4/13_What_is_Aquaponics_files/droppedImage_1.png
CHP OVERVIEW



CHP  Combined Heat and Power
One fuel source for multiple types of output power
 Electricity
 Thermal Energy
High overall efficiency
Fuel
Thermal
CHP System
Electrical

Develop models to guide in the development of an
advanced energy system for aquaponics

System level design of an environmentally responsible
and economical system capable of reducing carbon
emissions through higher efficiency

Create a simulation tool to aid in the designing and
selection of aquaponics energy systems

Greenhouse Environment between 45-60% relative
humidity and 55°F-85°F

Rearing Tank sizes ranging from 1,000-20,000 gallons

Maintain Tank Temperature Between 75°F-85°F

Consider both natural and artificial lighting
DESIGN CONSTRAINTS: POWER PRODUCTION

Provide power to aerate, heat, and pump tank water

Provide power for artificial lighting

Operate on Natural Gas

Continuous Operation With Exception for Maintenance

Less CO2 emissions than Milwaukee Emission Statistic

Lowest Cost/Least Environmental Impact
INITIAL PLANS

Mechanical
 Natural
Gas Engine with Heat Exchangers
 Supply
mechanical demand for:
Pumps
 Blowers

 Heat

exchangers to Provide heat for aquaponics tank(s)
Electrical
 Commercial
 Supply
CHP generator set
electricity for:
Pumps
 Lighting

 Provide
heat for aquaponics tank(s)
ELECTRICAL VS. MECHANICAL

Engine Trouble




Introducing lubrication (2-stroke)
Maintenance cycle
Space requirements
Efficiency of Heat Exchangers
MOVING FORWARD WITH ELECTRICAL SYSTEM


Took system level approach to pairing CHP and
aquaponics using commercially available CHP generators
Selected Marathon ecopower
Borrowed from: mathonengine.com
MARATHON ECOPOWER


Estimated installed system cost approximately $35,000
4000 hour maintenance interval
Specifications
Electrical Power
Thermal Power with max. flow
temp. 167 °F [75 °C]
Overall Efficiency
Engine
Exhaust Gas Figures [at 5% O2]
Grid Feed [Single Phase]
Sound Level
Dimensions/ Weight
Approvals
2.0 – 4.7 kW
6.0 – 12.5 kW
>90% (approx. 25% electrical + approx 65% thermal)
Single-Cylinder, 270 cm3, 1,700 – 3,600 rpm
NOx < 1.98 mg/ft3 CO < 11.33 mg/ft3 Temp < 194 °F [90 °C]
250 VAC, 50/60 Hz, Power Factor = 1
< 56 dB [A]
54 in. L x 30 in D x 43 H 858 lb
CE – Certificate, ETL - Approved
THERMAL MODELING
qevap , surf
Atmosphere
Ta , pa , P
qconv , surf
Water Level
Tw , hw , pw
Ground



Tg
qconv , wall
qcond ,base
CHP system sized for thermal load
 Point of most efficient operation
Model used to approximate thermal loading
Surface convection and evaporation, wall convection, base
conduction, and hydroponic tank losses

Evaporation (Two Models)
 (R.V. Dunkle 1961) Based on model of distillation pond
evaporation


 p  pa 
q e  0.0254   T w  T a    w
T

460

 a
39

p

a 



1 3
 pw
 p a  hw
(W.S. Carrier 1918) Empirical model based on indoor swimming
pools
 98.7  0.43V 
G   0.491 
 pw  pa 
h fg

Surface Convection
 Related to surface evaporation (I.S. Bowen 1926)
 Tw  Ta  P
 0.004943 

qe
p

p
14.7
a 
 w
qc

Wall Convection
 Based on non-dimensionalized analysis of flat plate
convection
N u L  0.13  G rL P r 
Nu L  hL k

1/ 3
G rL  g   L  T 
2
3
Pr  C p  k
Hydroponics Tank Losses
q&g ro w b ed  m&g ro w b ed c p , w a ter  T tan k  T retu rn 
2
PSYCHROMETRIC CHAMBER TESTING
Tank water temperature (F)
Atmospheric temperature (F)
Relative humidity (%)
Total run time (min)
Trial 1
~72
50
50
100
Trial 2
70
60
31
210
Temperature [F]
System Temperatures
80
Water
Atmospheric
60
40
0
0.5
1
1.5
2
2.5
3
3.5
2.5
3
3.5
Heater Power [BTU/hr]
Humidity [%]
System Relative Humidity
0.35
0.3
0.25
0
0.5
1
1.5
2
System Input Power
400
Raw Power Input
Averaged Power Input
200
0
0
0.5
1
1.5
2
Time [hr]
2.5
3
3.5
Evaporation Rate Over Time
0.12
Evaporation [lbm/hr]
0.1
0.08
0.06
0.04
0.02
0
0
R.V. Dunkle
W.H. Carrier
Actual Mass Loss
0.5
1
1.5
2
Time [hr]
2.5
3
3.5
q&conv , surf  q&in  q&evap  q&conv , w all  m c p , w ater
dT w ater
dt
System Energy
200
150
Energy [BTU/hr]
100
50
0
-50
Surface Evaporation (Predicted)
Surface Evaporation (Actual)
Heater Power (Actual)
Surface Convection (Actual)
Surface Convection (Predicted)
Water Transient
Tank Wall Convection (Predicted)
-100
-150
-200
0
0.5
1
1.5
2
Time [hr]
2.5
3
3.5
THERMAL LOAD PROFILE
Property
Tank Temperature
Greenhouse
temperature
Relative Humidity
Flow Rate
Value
80
70
Units
F
F
50
67
F
GPM
Return Temperature 78
Tank Size
7 width
3.5 height
30 length
Number of Tanks
Rubber Liner
Lumber
R7 Foam Insulation
2
0.25
1.5
1.5
Thermal Losses For Aquaponics
System
Surface Evaporation
Tank Wall Convection
Base Conduction
0%
F
Ft
Inch
Inch
Inch
Surface Convection
Gardening Losses
16%
81%
2%
1%
AQUAPONIC SYSTEM PROPORTIONING

University of Virgin Islands (UVI)
 Raft

Style Commercial System
Proportioning Hydroponic Tank to Rearing Tank
 Hydraulic
Loading Rate
 Retention Time
 Feed Rate
POWER REQUIREMENTS

Pumping

Centrifugal Pump


Rearing Tank Aeration


Greater Stocking Density
Regenerative Blower


45% Efficiency (elec.-water)
64% Efficiency (elec.-water)
Artificial Lighting



Implemented in few cases
18 Hr daylight grow period
Faster Plant Growth
 
V olum etric Flow *P ressure D ifference
E lectrical P ow er
POWER CALCULATION METHODS
SYSTEM HEAT & POWER REQUIREMENTS
SIZED SYSTEM FOR MARATHON ECOPOWER
(11000 GALLON)
System Calculated Power:
Pumping: 0.64 Hp (460 W)
Aeration: 1.44 Hp (1.06 kW)
Lighting: 43.8 Hp (32.7 kW)
Thermal: 39000 Btu/hr (11.43 kW)
UNIVERSITY OF VIRGIN ISLANDS SYSTEM
USING DEVELOPED PROCEDURE (8240 GALLON)
Calculated Power:
Pumping: 0.50 Hp (370 W)
Aeration: 1.1 Hp (800 W)
Lighting: None
Thermal: None
UVI System:
Pumping: 0.50 Hp
Fish Tank Aeration: 1.5 Hp
RESULTS OF ECONOMIC ANALYSIS
Conditions:
 $35,000 installed system
cost
 Analysis uses current
utility pricing
 CHP system run using
thermal load following
 Net metering 1:1
 Replaces 75% efficient
natural gas water heater
Results:
 31,000 kWh Electricity
Generated Annually
 83,000 kWh Water Heating
 Using 462,000 cu.ft
natural gas ($4,300)
 $3,000 Annual Benefit
 12 year simple payback
 10 year payback with 3%
inflation
 No incentives applied
RESULTS OF ENVIRONMENTAL ANALYSIS
Results:
 16.4 tCO2 avoided annually based on
Milwaukee emissions profile

14.5 tCO2 avoided annually based on National
emissions profile

Equivalent to approximately 2.8 cars and light
trucks not used


20.4 MPG
11,720 Miles

To provide a selection tool to farmers to assist in
incorporating CHP into efficient aquaponics operations
QUESTIONS