Thermal Comfort Performance Field Investigation of a Residential Forced- - Air Heating and Cooling System with High Sidewall Supply Air Outlets Bill Rittelmann, IBACOS Building Enclosure Technology and Environment Council June 12 th, 2008
Outline Introduction Project Overview HVAC Systems TCPI Results Heating Performance Cooling Performance Conclusions Acknowledgements
Introduction
Introduction High sidewall diffusers ASHRAE provides design guidelines for acceptable performance in cooling applications No guidelines exist for heating applications Laws of physics suggest that poor performance can be due to: High outlet air temperature Low outlet velocity Floor diffusers Identical design guideline issues Laws of physics help overcome low velocity heating issues, but high outlet temperatures can still lead to stratification
Introduction Thermal Comfort Standards ASHRAE Standard 55 Not intended to measure the thermal comfort performance Doesn t stipulate room-to-room temperature differences Time is not a criterion ACCA Manual J Room-to-room variation 2 F Ideal, 4 F Allowable No protocol for measurement ASHRAE Standard 113 Air Diffusion Performance Index ADPI Evaluates thermal comfort performance within single room Criteria include space and time
Introduction Thermal Comfort Performance Index (TCPI) Application of ASHRAE Standard 55 criteria Predicted Mean Vote (PMV) - ±0.5 (90% satisfied) Neutral comfort conditions Summer: 23.9 C, 50% RH, room air velocity of 0.1 mps, Clothing factor (CLO) = 0.51, metabolic rate (MET) = 1.3 Winter: 21.0 C, 40% RH, room air velocity of 0.1 mps, Clothing factor (CLO) = 1.0, metabolic rate (MET) = 1.3 Measurement protocol modified Standard 113 24-hour evaluation period PMV calculated every minute TCPI = % of measurements that satisfy criteria Local discomfort (stratification) also evaluated
Project Overview
Project Overview & Purpose Characterize heating performance of high sidewall supply air outlets in an energy-efficient house Research Houses Fort Wayne, IN Floor area 2,139 ft² Typical Production House Full basement HERS Index - 87
HVAC Systems
HVAC Systems Redundant Central Forced-Air Systems Permanent system Floor diffusers Gas-fired heat, 2-stages, 26/40 MBH input 2-stage cooling, 3-tons Temporary system High sidewall diffusers Fancoil Electric heat, 3-stages, 5, 10, & 15 kw 2-stage cooling, 3-tons
Its Tough Changing an Industry
HVAC Systems Redundant Central Forced- Air System with Ductwork Inside Conditioned Space High Sidewall Supply Air Outlet of Redundant System
HVAC Systems System Fancoil 1 Furnace Total Airflow (L/s) Heating Capacity Stage 1 (5 kw) Stage 2 (10 kw) Stage 3 (15 kw) 577 28.6ºC 2 35.5ºC 2 42.2ºC 3 399 31.9ºC 3 N/A N/A 278 35.7ºC 3 N/A N/A 295 N/A 50.2ºC 3 N/A 235 46.3ºC N/A N/A 321 N/A 49.2ºC 3 N/A 1.) For instances throughout the remainder of this paper, an airflow of 577 L/s is inferred for all heating capacity stages unless otherwise noted. 2.) Measured steady-state supply air temperature 3.) Calculated steady-state supply air temperature
TCPI Results
Results Heating TCPI High Sidewall Diffusers
Results Heating TCPI Floor Diffusers
Results TCPI Cooling
Heating Performance
Results - Stratification
Results - Stratification
Results - Stratification
Results - Stratification
Results Space Temperature
Results Space Temperature
Results Space Temperature
Results Space Temperature
Results Space Temperature
Results Space Temperature
Results Space Temperature
Cooling Performance
Results - Stratification
Results - Stratification
Results Fan Control
Results Thermostat Control
Conclusions High sidewall supply air outlets provide slightly better thermal comfort performance than the floor diffusers for both heating and cooling operation. Reduced head-to-toe temperature stratification More uniform room-to-room temperatures TCPI of the floor diffuser system was noticeably worse at extremely cold outdoor temperatures. Cooling TCPI of both systems similar High stage = 95% Low stage = 82% Cooling stratification is noticeably better (lower) in the high sidewall system and is well within the acceptable ASHRAE limit of 3.0 C for both systems.
Conclusions Additional fan operation Reduces stratification High stage heating both systems Medium stage heating high sidewall system only Virtually no difference Low stage heating both systems Cooling performance stratification Floor diffuser system slightly worse (higher) Both systems were well within acceptable limits Fan operation continuous vs. cyclical Slightly better whole-house temperature uniformity during highstage cooling in high sidewall application
Conclusions Thermostat location Multi-point strategy provided better whole-house comfort than a single-point strategy for both systems, both modes, and all stages.
Acknowledgements U.S. DOE Building America program National Renewable Energy Laboratory (NREL) Cardinal Glass Corporation Carrier Corporation