Evaluation of Space Humidity Control and System Energy Usage for Conventional and Advanced Unitary Equipment Michael J. Witte and Robert H. Henninger GARD Analytics, Inc. ASHRAE Winter Meeting, Seminar 39 “Designing for Dehumidification and Mold Avoidance” January 24, 2006, Chicago, IL (Rev. May 31, 2006) Revisions on slides 12, 15-18, 20, 27-30, 32-36

Rev. May 2006ASHRAE Seminar, M.J. Witte2 Acknowledgements Preview of ASHRAE Research Project 1254RP Evaluating the Ability of Unitary Equipment to Maintain Adequate Space Humidity Levels, Phase II Co-funded by U.S. DOE through ARTI Based on ASHRAE 1121-RP, Phase I Evaluation Plan, Brandemuehl and Katejanekarn, Univ. of Colorado at Boulder, June 2001

Rev. May 2006ASHRAE Seminar, M.J. Witte3 Objectives Compare various unitary air conditioning system humidity control configurations for application to commercial buildings in terms of humidity control performance, operating costs, and lifecycle costs to each other as well as to conventional unitary equipment Develop guidelines to help HVAC engineers and practitioners identify the important application characteristics and climate factors that determine which option is most appropriate

Rev. May 2006ASHRAE Seminar, M.J. Witte4 Project Overview EnergyPlus hourly whole-building simulations 7 Building types 10 Locations 18 System types 2 Ventilation standards Humidity control and energy use Economic analysis Guidelines and recommendations

Rev. May 2006ASHRAE Seminar, M.J. Witte5 Building Types Small Office Restaurant Dining Area Large Retail Theater Classroom (South exposure) Classroom-12 Month (South exposure) Motel Guest Room (South exp.)

Rev. May 2006ASHRAE Seminar, M.J. Witte6 Locations Atlanta, GA Chicago, IL Dallas/Fort Worth, TX Miami, FL New York, NY Portland, OR St. Louis, MO Washington, DC Houston, TX Shreveport, LA

Rev. May 2006ASHRAE Seminar, M.J. Witte7 System Types: Case 0-2 Case 0 – Conventional DX System 400 CFM/ton All CFM/ton values are nominal “Typical” HVAC design practice 2-stage coil Case 1 – Base DX System 350 CFM/ton (different equipment than Case 0) Better dehumidification design practice Case 2 – DX with Improved Dehumidification 300 CFM/ton Modified coil, compressor, etc.

Rev. May 2006ASHRAE Seminar, M.J. Witte8 System Types: Case 3-4 Case 3 – Base DX with Lower Airflow 300 CFM/ton Same coil and compressor as Case 1 Case 4 – Air-to-Air Heat Exchanger (AAHX) 350 CFM/ton (Case 1 equipment) Wrap-around HX Sensible effectiveness 0.4 No latent transfer Single-stage coil in all apps

Rev. May 2006ASHRAE Seminar, M.J. Witte9 System Types: Case 5 Case 5 – Subcool Reheat Coil 350 CFM/ton Normal mode same as Case 1 Enhanced dehumidification mode Standard mfr. option Switch modes if 50%RH setpoint not met

Rev. May 2006ASHRAE Seminar, M.J. Witte10 System Types: Case 6 Case 6 – Fan Control to Drain Coil 350 CFM/ton Normal mode same as Case 1 Fan off for short time when compressor cycles off No moisture re-evaporation Modeled by turning off latent degradation in DX coil model – no change in fan power consumption Ideal case – not achievable in real equipment Can also be thought of as variable capacity control

Rev. May 2006ASHRAE Seminar, M.J. Witte11 System Types: Case 7 Case 7 – Bypass Damper 350 CFM/ton Normal mode same as Case CFM/ton in bypass mode 50 CFM/ton bypassed Switch modes if 50%RH setpoint not met

Rev. May 2006ASHRAE Seminar, M.J. Witte12 System Types: Case 8 Case 8 – Hybrid DX with Desiccant 400 CFM/ton (Case 0) Desiccant condition outside air stream Mixed air to cooling coil Control to meet 50%RH setpoint Heat recovery to exhaust air Outdoor Exhaust Outdoor Supply Return

Rev. May 2006ASHRAE Seminar, M.J. Witte13 System Types: Case 9 Case 9 – Enthalpy Recovery Wheel 350 CFM/ton (Case 1) Enthalpy heat recovery OA and exhaust Bypassed when not beneficial 0.91 sensible eff. (constant) 0.85 latent eff. (constant)

Rev. May 2006ASHRAE Seminar, M.J. Witte14 System Types: Case 10 Case 10 – DX Outdoor Air Preconditioning DX Preconditioner Evaporator in OA stream Condenser in relief air stream 580 CFM/ton Standard mfr. option Run 1st Main DX System 350 CFM/ton (Case 1) Run as needed

Rev. May 2006ASHRAE Seminar, M.J. Witte15 System Types: Case 11 Case 11 – Base Dual Path Outdoor air system 2 DX coils in series 300 CFM/ton (Case 3) 150 CFM/ton overall 2 stages each 7.22C (45F) min supply Return air system 1 DX coil 400 CFM/ton (Case 0) 1 stage (last stage on)

Rev. May 2006ASHRAE Seminar, M.J. Witte16 System Types: Case 12 Case 12 – Dual Path + Enthalpy Recovery Outdoor air system 1 DX coil 350 CFM/ton (Case 1) 2 stages 7.22C (45F) min supply Return air system 1 DX coil 400 CFM/ton (Case 0) 1 stage (last stage on) Return Air Supply Air

Rev. May 2006ASHRAE Seminar, M.J. Witte17 System Types: Case 13 Case 13 – Dual Path + AAHX Outdoor air system 2 DX coils in series AAHX, 0.4 sensible, no latent 300 CFM/ton (Case 3) 150 CFM/ton overall 1 stage each 7.22C (45F) min supply Return air system 1 DX coil 400 CFM/ton (Case 0) 1 stage (last stage on)

Rev. May 2006ASHRAE Seminar, M.J. Witte18 System Types: Case 14 Case 14 – Dual Path + Desiccant Outdoor air system 1 DX coil 350 CFM/ton (Case 1) 2 stages 7.22C (45F) min supply Return air system 1 DX coil 400 CFM/ton (Case 0) 1 stage (last stage on) Exhaust Air Outdoor Air

Rev. May 2006ASHRAE Seminar, M.J. Witte19 System Types: Case Case 15 – Demand Controlled Ventilation 350 CFM/ton (Case 1 equipment) Pseudo DCV Minimum OA based on cfm/sf spec from Std. 62 Plus cfm/person OA tracks Occupancy Schedule Case 16 – Dual Path + DCV Case 11 equipment Pseudo DCV – same as above

Rev. May 2006ASHRAE Seminar, M.J. Witte20 System Types: Case 17 Case 17 – Base DX with Free Reheat Case 1 equipment Overcool to meet 50%RH setpoint Case 1 sizing – no oversizing for latent “Free” hot gas reheat from DX condenser Reheat capacity 100% of condenser heat rejection No fan penalty for extra reheat coil Dehumidify only when sensible load No operation for latent-only load

Rev. May 2006ASHRAE Seminar, M.J. Witte21 2 Ventilation Standards Standard Referenced by many building codes Standard Current standard Ventilation rates cfm/sf, cfm/person Design occupant density (some change)

Rev. May 2006ASHRAE Seminar, M.J. Witte vs 2001 Ventilation Building Total* cfm/sf Case 0** Base %OA Total* cfm/sf Case 0** Base %OA Office0.1426%0.0918% Retail0.3041%0.2344% School0.7553%0.3744% Restaurant1.4361%0.7243% Motel0.0918%0.1122% Theater2.1464%0.7737% *Combined cfm/sf plus cfm/person vent rate **for Atlanta

Rev. May 2006ASHRAE Seminar, M.J. Witte23 System Sizing Sizing simulations using ideal system ASHRAE 0.4% dry-bulb day (2001 HOF) Design ventilation rate “Purchased Air” Peak sensible coil load Net (after fan heat) Plus 10% for oversizing All systems sized to this net sensible capacity Except enthalpy wheel sensible capacity credit at design dry-bulb – smaller DX capacity

Rev. May 2006ASHRAE Seminar, M.J. Witte24 Key Modeling Assumptions Existing simulation tool features DX coil moisture re-evaporation (continuous fan) Moisture capacitance (EMPD model) New simulation tool features developed in this project 2-Stage DX coil Multi-mode DX coil switchable enhanced dehumidification mode e.g. subcool reheat Performance curves based on published manufacturer’s data

Rev. May 2006ASHRAE Seminar, M.J. Witte25 Life Cycle Cost Equipment installed costs Popular cost estimating guide for base cost Technical literature for option costs One option is actual mfr quote Approximate! Costs are highly variable, especially for non-standard options State average commercial energy costs 15-yr energy cost projections from EIA

Rev. May 2006ASHRAE Seminar, M.J. Witte26 Selected Results

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Rev. May 2006ASHRAE Seminar, M.J. Witte32 Retail 2004 Humidity Control

Rev. May 2006ASHRAE Seminar, M.J. Witte33 Retail 2004 Energy Cost

Rev. May 2006ASHRAE Seminar, M.J. Witte34 Retail 2004 Life Cycle Cost Adequate humidity control and LOWER LCC Case 12 - Dual Path w/Enthalpy Wheel Case 9 - Base DX w/Enthalpy Wheel

Rev. May 2006ASHRAE Seminar, M.J. Witte35 Restaurant 2004 Humidity Control

Rev. May 2006ASHRAE Seminar, M.J. Witte36 Restaurant 2004 Life Cycle Cost Adequate humidity control but HIGHER LCC Case 17 - Base DX w/Free Reheat Case 14 - Dual Path w/Desiccant Less-adequate humidity control but LOWER LCC Case 12 - Dual Path w/Enthalpy Wheel

Rev. May 2006ASHRAE Seminar, M.J. Witte37 Trends Relative humidity control across system types Fairly constant from location to location for a given combination of building type and ventilation standard Overall number of high humidity hours changes across the board when changing locations, but the relative pattern of humidity control remains very similar

Rev. May 2006ASHRAE Seminar, M.J. Witte38 Challenging Applications Restaurant, Theater, Motel in humid climate Large number of hours with moisture load but little or no sensible load – morning, evening, night Active humidity control required Desiccant Reheat

Rev. May 2006ASHRAE Seminar, M.J. Witte39 Less Challenging Applications Retail, Office, School in humid climate Restaurant, Theater, Motel in moderate climate Load reduction for cost savings and less humidity Enthalpy Wheel DCV

Rev. May 2006ASHRAE Seminar, M.J. Witte40 Conclusions Generalizations based on one set of assumptions Results tables allow some extrapolation to other cases New simulation tool features provide designers tool to evaluate specific applications Questions...