Christopher Price Component Level HVAC Control NIST Project
Seminar Meeting 11/2013 Christopher Price Component Level HVAC Control NIST Project Motivation Background Cascaded Control Air Volume Systems
Overview Motivation Background Cascaded Control Air Volume Systems Hydronic Radiators Future Work DMPC Control Project (NIST)
Motivation DMPC Control Project (NIST) Advanced control algorithms to generate system set points Reduced energy consumption and cost through improved efficiency Full energy savings when components have adequate tracking Research is under the NIST project which is the DMPC for Building Energy Systems umbrella. Remind everyone what the DMPC does, i.e. generates set points for subsystems/individual components to follow. It is therefore important that those components provide adequate set point tracking to take full advantage of the DMPC energy savings potential. Also can provide ways of increasing actuator/component lifetime by eliminating common problems with control algorithms. Motivation Where I Fit Vapor Compression Cycle
Background Vapor Compression Cycle Quickly go though the cycle in order to explain the purpose of the expansion valve which will lead into the problem of valve hunting. (2010) Eliot & Rasmussen: On Reducing Evaporator Superheat Nonlinearity Expansion Valves Background Automatic Expansion Valve Capillary Tube
Thermostatic Expansion Valve Automatic Expansion Valve Capillary Tube Explain the development of the controls for the VCC system and what they are good at controlling. It is the combination of the AEVs ability to reject disturbances from pressure and the TEVs ability to regulate SH that could be combined to make the HEV/Cascaded control loop. Evaporator SH depends on evaporator pressure, and outlet temperature. So AEVs are good at rejecting disturbances related to pressure but do not offer SH regulation while TEVs do control SH but there is a significant time lag due to the position of the bulb. Hybrid Expansion Valve
Background Hybrid Expansion Valve (2009) Eliot & Rasmussen: Evaporator Superheat Regulation Via Emulation of Semi-Active Flow Control Block Diagram Cascaded Control
Explain the construction of this loop. Then explain the linearization that comes from this construction. (i.e. mass flow map Km(v) appears in the numerator and denominator) . Also should point out the G(s) and H(s) part of this. So basically the SH appears to have been linearized to the slow control loop. Valve Position to Mass Flow
Cascaded Control Valve Position to Mass Flow Mass Flow to Pressure Mass Flow to Superheat (2009) Eliot & Rasmussen: Evaporator Superheat Regulation Via Emulation of Semi-Active Flow Control Apply same control idea to air handlers Two main types:
Air Volume Systems Apply same control idea to air handlers Two main types: Constant Volume Systems Flow rate constant, temperature varied Variable Air Volume Systems* Varied flow rate, temperature constant VAV Systems Schematic Describe the basic operation of the VAV system describing the individual components and the operating principles like fan maintaining constant static pressure and the damper opening and closing to allow more air through to the space. Damper Types VAV Systems Parallel Blade Opposed Blade Single Blade
Dont forget to mention the damper speed restriction somewhere in here! Parallel Blade Opposed Blade Single Blade 2009 ASHRAE Handbook Fundamentals Arrow United Industries Damper Characteristics
VAV Systems Damper Characteristics Parallel Blade Opposed Blade 2009 ASHRAE Handbook Fundamentals Traditional PID vs. Cascaded Control
VAV Systems Traditional PID vs. Cascaded Control Simulation Model Damper Model VAV Systems
(2010) Yamakawa: Compensation of Manual Reset for PID Controller VAV Systems Traditional PID Control
Jump to slide showing the damper characteristics. VAV Systems Cascaded Control
PID Control Cascaded Control Case MAE RMS 20% 0.4461 0.1239 Low Flow 0.743 0.263 35% 0.4274 0.1052 Mid Flow 0.351 0.097 50% 0.8246 0.2489 High Flow 0.268 0.047 80% 1.9682 0.5446 The ones with orange have damper hunting present. Lessons: 1. Have to tune the damper for lowest expected load condition b/c of hunting behavior 2. Reduced temperature tracking because of small control gains 3. Cascaded control loop eliminates the presence of hunting while improving performance Shown cascaded control works for refrigerant and air mediums
Hydronic Radiators Shown cascaded control works for refrigerant and air mediums Apply control design to water radiator systems Currently working on validating results from Tahersima 2013 paper Equations Hydronic Radiators Radiator: Room: Valve:
(2013) Tahersima: Analytical Solution for Stability-Performance Dilemma for Hydronic Radiators Motivation Hydronic Radiators
(2013) Tahersima: Analytical Solution for Stability-Performance Dilemma for Hydronic Radiators Study the effect of sampling rate on performance of cascaded loop
Future Work Study the effect of sampling rate on performance of cascaded loop Proper tuning of cascaded loop control Application of cascaded control to positive displacement components (fans/pumps) Alternate control structures (e.g. feed forward control) Questions?