ASHRAE Boston Chapter Meeting Designing AC Refrigeration Systems Lessons Learned February 11, 2014

Explanation of the refrigeration cycle. Compressors. Benefits and operating characteristics. -Reciprocating -Screw -Scroll Condenser types and benefits -Air cooled -Evaporative Expansion Valves -Thermostatic -Non- Balanced port -Balanced port -Electronic Evaporator Design -Fins per inch -Moisture carryover -Distributors

Standard RTU Concerns -Capacity control at part loads Split Systems Concerns -Piping concerns -Receiver -Pump down solenoid valve -Oil Separator 100% Outdoor Air DX Unit Concerns -Interlaced evaporators vs. parallel or series -Precise capacity control Compressor staging Compressor unloading Scroll- 66% or down to 20% (variable speed) Hot gas bypass to evaporator Tight head pressure control Fan speed control vs. flooded condenser

HVAC Engineers Understanding of a Refrigeration System Chilled Water 55 F 45 F CHILLER 95 F 85 F Condenser Water Air Out 55 F RTU 95 F DB 73 F WB Air In

Basic Refrigeration System Air-cooled Water-cooled Evaporative Condenser Prime Mover Motor Engine Steam Turbine Compressor Scroll Reciprocating Helical rotary (screw) Centrifugal Evaporator Air cooling coil Shell & tube (liquid chiller) Special (process) Metering Device Capillary tube Orifice TXV Level control Electronic

Basic Refrigeration System E+Q out Condenser Compressor Metering Device E in Typically 30% of Q Evaporator Q in

Basic Refrigeration System 100 F-195 psi Condenser Compressor R-22 Metering Device Capillary tube Orifice TXV Level control Electronic Evaporator 45 F- 76 psi

Reciprocating Compressor

Reciprocating Compressor Unloader

Screw Compressor

Scroll Compressor

Compressor Efficiencies Capacity % Reciprocating Helical Rotary Scroll KW/Ton KW/Ton KW/Ton 100 0.87 0.70 0.80 50 50% 42% NA 25 35% 26% NA Part Load Performance (% Power) Performance at 85 F Cond

Air Cooled Condenser

Evaporative Condenser

Condensers Efficiencies R-22 Ambient temp Sat. liquid temp Ambient minus liquid Head pressure 95 F db 115 F db 20 F db 243 psi 78 F wb 90 F db 12 F db 168 psi Aircooled Watercooled Evapcond 78 F wb 85 F db 7 F db 156 psi

Thermostatic Expansion Valve

Oil Separator

Filter-Drier

Suction Accumulator

Hot Gas Bypass

Refrigerant Distributor

Refrigerant Distributor Refrigerant Distributor

Refrigerant Distributor

1RTU with Chiller

Parallel Evaporator Coils

Interlaced Evaporator Coils

Refrigeration Design for Air Conditioning Systems Attendees Quiz 1. What is the most common type of compressor used in RTU s today? A. Reciprocating B. Screw C. Scroll D. Centrifugal 2. What is the advantage of an evaporative condenser compared to an air cooled condenser? A. Cost B. Size C. Maintenance D. Efficiency 3. What is the advantage of an air cooled condenser compared to an evaporative condenser? A. Cost B. Size C. Maintenance D. All of the above

4. What could be the major problem with too many fins per inch on an evaporator? A. Cost B. Pressure drop C. Moisture carryover D. Weight 5. Approximately what percentage of the condenser load is due to the compressor? A. 0 % B. 20% C. 30% D. 50% 6. When should a receiver be used in a system? A. All the time B. Anytime the system is on the roof C.Anytime the condenser cannot hold all of the liquid refrigerant D. When required by local codes 7. Which is the preferred method of hot gas bypass for RTU s? A. Hot gas to suction line B. Hot gas to evaporator outlet C. Hot gas to the evaporator inlet D. No preferred method

8. What is the preferred method for head pressure control? A. Flooded condenser B. On-off fan control C. Modulating dampers D. Fan speed control 9. Which pipe will cause problems if over sized? A. Liquid B. Hot gas C. Suction D. All of the above 10. Which pipes should be insulated? (Circle all that apply) A. Suction B. Hot gas C. Liquid D. None