Course adjustment EnergyPlus (E+) - SIMERGY - - PowerPoint PPT Presentation

BEM Class 7 HVAC-2

Course adjustment

• EnergyPlus (E+) - SIMERGY

– http://simulationresearch.lbl.gov/projects/gui – http://simergy-beta.lbl.gov/ – Download please for use in class demo sessions (April classes)

Review from class 6

• Discussion: Principles for Zoning

Exposures Usage types Schedule Tenancy & Metering On shared HVAC equipment

Review from class 6

• EQuest tutorial: what do you need to know to

set up HVAC system in EQuest ?

• How do you obtain this data?
• How do you know if it’s right?

Review from class 6 HVAC systems and components

Packaged assemblies – air-handling units, rooftop units

HVAC Equations Solving from Load to Flows

Air QBTUH = CFM x dT x .018 x 60 (.018 x 60 = 1.08) CFM = QBTUH / (dT x 1.08) typ dT = 20 dF Water QBTUH = GPM x dT x 8.33 x 60 (8.33 x 60 = 500) GPM = QBTUH / (dT x 500) typ dT = 10 dF

HVAC Equations Solving from Flows to Power

Fan HP = CFM x dP / (6356 x FE)

dP is total pressure in inches of water column, Typ dP = 3 in w.c. FE (fan efficiency) typical value = .65

Pump (closed loop) HP = GPM x dP / (1715 x PE)

dP is dynamic pressure created by pump in psi (for an open loop pump, dP is “lift” in

feet of head and the conversion constant is 3956; 2.31 ft of head = 1 psi)

PE (Pump Efficiency) typical value = .65

Convert Brake Horsepower to Electrical Power

HP x .746 = KW

HVAC Component Characterization Pump & Fan Curves

• Component

performance model based on mfr (test) data

• Plots output (flow) vs

pressure

• Dampers and valves

also have curves – flow vs position

HVAC Component Characterization

Part Load Factors – Boilers & Chillers

• Efficiency vs Load
• Boilers & Chillers lose

efficiency at part-loads (with exception of most current generation of hi- efficiency equipment)

• Most operation is at part-

loads

HVAC Equipment Variables Constant vs Variable Volume

– In CV systems, part-loads typically met by some form of simultaneous heating & cooling (eg – dual duct, re-heat) – Significant electrical savings in slowing down pumps or fans when possible

• Dampers for variable air volumes delivered to rooms
• Variable frequency drive controls on fans

HVAC Equipment Variables

Outside Air control and Economizer

• Minimum OA for ventilation when heating or cooling
• Match OA to occupancy (DCV)
• Maximize OA when cooler than RA (cooling)

New Construction vs Existing

• ASHRAE “Appendix G” (90.1)

– Models for comparison only to other models, not for projection of actual energy use

• Why?

Model “Calibration”

• Matching model results to metered data

– How close a match? – What granularity?

• How is model calibration done?

– Tune individual parameters, such as….. – But which ones and how much? Multiple solutions….but only one actually matches conditions – Use of building data to inform