Application of MCHE in Commercial Air Conditioners

Application of MCHE in Commercial Air Conditioners
Mustafa Yanik and Jiang Jianlong – Danfoss AC/R - Heat Exchangers
Chillventa 2012 Nuremberg, Germany October 9, 2012
Refrigeration and A/C Controls Division Date | 1

Outline
• Brief Intro to MCHE
• MCHE Condenser vs Evaporators – Drivers/Challanges
• Implementation of MCHE Evaporators in Commercial AC
• Basic Features of MCHE Evaporator for AC
• Refrigerant Distribution vs Performance
• Air Flow Distribution vs Performance
• Two Row MCHE Coils in Reversible Systems
• Multi Circuit Coils – Row Split
• Comparison of MCHE w/ FT in a 20kW System
Refrigeration and A/C Controls Division March 15, 2012 | 2

Brief Intro to MCHE
5
4
3
1. Baffle – for multi pass
2. Microchannel tube
3. Header
4. End cap
5. Side plate – for protection
2
6. Enhanced fins with louvers
1
6
1
7
• All Aluminum Construction
• Furnace Brazed
Refrigeration and A/C Controls Division March 15, 2012 | 3

MCHE Condensers vs Evaporators
Condenser Evaporator
Charge Reduction 70% 25%
Size Reduction 66% 66%
Weight Reduction 70% 70%
Corrosion Resistance Galvanic Formicary
Low Raw Material
Cost
√
√
High Performance at
Affordable Cost
√
√
Reduced Air Side
Pressure Drop
Drivers
√
√
Refrigerant
Distribution
Impact of Air Mal-
Distribution
Intermediate
Headers
Water Condensate
Challenges
Condenser
Non Issue
Negligible
Ok
Not Applicable
Evaporator
Distributor Design
Critical
Critical
Not Acceptable
Vertical
Orientation - Fin
Design Critical
Frost Accumulation Not Applicable Challenging
Refrigeration and A/C Controls Division March 15, 2012 | 4

Basic Construction of MCHE Evaporators
• Slab Coil
• Two Row – Folded/Formed
• A Coil – Folded/Formed
Refrigeration and A/C Controls Division March 15, 2012 | 5

MCHE Refrigerant Distributor Design
• General Description : Distributor Tube within the header with orifices
• Critical Features:
• Flow Pattern in Distributor Tube
• Size of the distributor tube
• Spray Pattern
• Location of distributor tube
• Spacing of orifice holes
• Angular location of the orifice holes
• Diameter of orifice holes
• Pressure Drop Equalization
• Multiple Outlet Connection
• Secondary Outlet Manifold
• Size of Outlet Manifold
• Dual Inlet Connections
Refrigeration and A/C Controls Division March 15, 2012 | 6

Simulation to calculate Sensitivity of MCHE Evaporator to
Refrigerant Distribution
• Method
• Divide a MCHE coil into 2 sections
• Prescribe varying refrigerant flow to each section
• Coil Description
• Size : 1000 mm by 1000mm and 25mm deep
• 23 FPI fin density
• MPE: 26 channels – 0.635mm by 0.74mm
• Thermal Conditions
• Refrigerant – R410A
• Air Temperature: 80/67 DB/WB
• Air Velocity = 500 ft/min (2.54 m/s)
• Tliq = 100F
• Tsat_evap = 52F (10.6 C)
1 2
Refrigeration and A/C Controls Division March 15, 2012 | 7

Q / Q_uniform
Effect of Refrigerant Flow Mal-distribution on MCHE Coil Capacity at
Various SH
100%
95%
90%
85%
80%
75%
SH = 13F (7.2C)
SH = 10F (5.6C)
SH = 7F (3.9C)
SH = 4F (2.2C)
70%
65%
60%
50%/50% 45%/55% 40%/60% 35%/65% 30%/70%
mfr_left / mfr_right
Refrigeration and A/C Controls Division March 15, 2012 | 8

Q / Q_uniform
Effect of Refrigerant Phase Mal-distribution on MCHE Coil Capacity
at Various SH
100%
95%
90%
85%
80%
75%
SH = 13F (7.2C)
SH = 10F (5.6C)
SH = 7F (3.9C)
SH = 4F (2.2C)
70%
65%
60%
20%/20% 25%/15% 30%/10% 35%/5%
x_left / x_right
Refrigeration and A/C Controls Division March 15, 2012 | 9

Simulation to calculate Sensitivity of MCHE Evaporator to Air Flow
Mal-distribution
• Method
• Divide a MCHE coil into 2 sections (left to right and top to bottom)
• Assume air flow does not effect refrigerant flow
• Prescribe varying air flow to each section
2
1
1 2
Refrigeration and A/C Controls Division March 15, 2012 | 10

Q / Q_uniform
Effect of Air Mal-distribution (Left to Right & Top to Bottom) on
MCHE Coil Capacity at 10F SH
100%
95%
90%
85%
80%
75%
Air Mal Distribution Left to Right
Air Mal Distribution Top to Bottom
70%
65%
60%
50%/50% 60%/40% 70%/30% 80%/20%
mfr_air_1 / mfr_air_2
Refrigeration and A/C Controls Division March 15, 2012 | 11

Circuit Orientation and air mal-distribution in MCHE
Evap Coils
Refrigeration and A/C Controls Division March 15, 2012 | 12

Circuit Orientation and air mal-distribution in FT Evap
Coils
What is ok for MCHE is not ok for FT and vice versa.
Refrigeration and A/C Controls Division March 15, 2012 | 13

Air Mal Distribution in Condensers – Self Correcting
Refrigeration and A/C Controls Division March 15, 2012 | 14

Air Mal Distribution in Evaporators – Self Destructing
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Two row MCHE Coils in Reversible Systems
• Two critical features
• Folded/formed coils without intermediate headers
• Eliminate refrigerant mal-distribution
• Counter-flow in Condenser mode, hence parallel flow in evaporator mode
• Ensure condenser sub-cooling
• About 10% increase in HP Capacity w/ 4% drop in Cooling Capacity based
on test data
Refrigeration and A/C Controls Division March 15, 2012 | 16

MCHE Evaporators for Multi Circuit Systems
• Interlaced Circuiting not
available
• Face Split Configuration
• Side by Side Split is preferred
• Easier to Distribute Refrigerant
• Higher refrigerant velocity and
performance
• Smaller headers – lower cost
• Row Split
• Thermodynamic advantage for
upstream system
• Lower capacity in the downstream
system preferred
Circuit 1 Circuit 2
Circuit 1 Circuit 2
Refrigeration and A/C Controls Division March 15, 2012 | 17

Comparison of FT Coil w/ MCHE in a 20 KW Commercial AC
• FT Coil Description
• 8mm OD internally enhanced Cu
tubing
• 1 inch vertical spacing
• 0.866 inch horizontal spacing
• Enhanced Fins with Louvers
• 4rows
• Face Area 9 sqft
• MCHE Description
• 16mm MPE tubing
• 16 ports – 0.63mm by 0.74mm
• Folded 2 row
• 16 fin/inch
• Two inlets / Two outlets
• Face Area 9 sqft
Refrigeration and A/C Controls Division March 15, 2012 | 18

Comparison of FT Coil w/ MCHE in a 20 KW Commercial AC
• Coil Weight Reduced by 66%
• Coil Depth Reduced by 50%
• Refrigerant Charge Reduced by 18%
Refrigeration and A/C Controls Division March 15, 2012 | 19

Questions?
Refrigeration and A/C Controls Division March 15, 2012 | 20