Demand flow for air cooled chillers
For more efficient operation of an air cooled chiller, a refrigerant pump and bypass valve connected in parallel feed refrigerant from the condenser to a receiver. The pump is activated in response to pressure in the condenser; the bypass is used otherwise. Further efficiency is provided by controlling the condenser fan based on power consumption by the air cooled chiller and/or resetting a set point of the evaporator to meet load conditions. An expansion valve for the evaporator is controlled based on chilled water temperature, such as Delta T, or information from an air handling unit. Feedback of valve setting or position, air temperature, valve size, and/or importance of an air handling unit may be used to control the flow of chilled water. In addition to or an alternative to control of the chilled water flow, the refrigerant temperature may be controlled based on information from the air handling unit.
1. An air cooled chiller comprising:
a refrigerant loop having a compressor fluidly connected to a condenser, the condenser fluidly connected to an evaporator, and the evaporator fluidly connected to the compressor;
a refrigerant pump and isolation valve in the refrigerant loop and fluidly connected in parallel between the condenser and the evaporator; and
a receiver between the pump and the evaporator and fluidly connected with an output of the refrigerant pump.
2. The air cooled chiller of claim 1 further comprising a pressure sensor in the condenser, the refrigerant pump activated in response to a pressure from the pressure sensor being above a threshold and deactivated in response to the pressure from the pressure sensor being below the threshold.
3. The air cooled chiller of claim 2 wherein the isolation valve is configured to open when the refrigerant pump is not running and configured to close when the refrigerant pump is running.
4. The air cooled chiller of claim 1 further comprising a condenser fan positioned to cause air flow across the condenser.
5. The air cooled chiller of claim 4 wherein the condenser fan comprises a variable drive responsive to a measure of power used by the air cooled chiller.
6. The air cooled chiller of claim 1 wherein the receiver is fluidly connected between (i) the refrigerant pump and isolation valve and (ii) the evaporator.
7. The air cooled chiller of claim 1 wherein the evaporator comprises parallel evaporator parts and corresponding expansion valves, the expansion valves configured to fluidly connect and disconnect the evaporator parts individually based on chilled water temperature.
8. The air cooled chiller of claim 1 further comprising a controller configured to control flow of chilled water in the evaporator as a function of two or more of a position of a valve in an air handling unit, a temperature of the chilled water at the air handling unit, a size of the valve in the air handling unit, and a priority of the air handling unit.
9. The air cooled chiller of claim 1 further comprising a controller configured to control refrigerant temperature as a function of a position of a valve in an air handling unit.