Presentation on theme: "Presentation for Florida Building Commission Regional AC Efficiency Workgroup May 9, 2008 Lennox Industries Inc."— Presentation transcript:
Presentation for Florida Building Commission Regional AC Efficiency Workgroup May 9, 2008 Lennox Industries Inc.
About Lennox Industries Inc.: Lennox is a U.S. Residential and Commercial HVAC Manufacturer Over 100 years young Over 6000 dealers Nationwide operations Four-time EPA Energy-Star Partner of the Year Three-time AHRI Performance Award Winner
Comparison Current System of Standards A Regional Scheme EnforcementProduct levelLocal level ManufacturerAny coil combination meets standard Distribution & supply concerns ContractorsProducts for every application & economic need Higher efficiency products only Issues around high efficiency cooling in humid climates…
Problem Statement: In Hot & Humid Climates, sensible load reduction can exacerbate indoor humidity problems. How shall we reduce energy consumption and still provide comfortable and healthy indoor environments? What changes (code and otherwise) will be most beneficial?
Comfort/Health For the cooling season: an indoor temperature of 75F to 77F, with an indoor humidity <55%* is a good goal. *we believe that occasional excursions above 60%, for not more than a few hours at a time, are actually OK.
Cooling Loads Cooling loads are composed of: “sensible” +“latent” = total Heat conduction Solar transmitted heat infiltration/ventilation Moisture from showers, cooking, etc. Expiration/perspiration of occupants Moist air infiltration/ ventilation The ratio of the sensible-to-total load is the SHR; It is determined by the house and its occupants.
Air Conditioner Operation An air conditioner sensible-to-total cooling ratio likewise describes how the unit cools and removes moisture under given conditions. The S/T ratio varies with: Indoor air flow rate Indoor temperature and humidity Outdoor temperature
Air Conditioner Operation The S/T ratio is typically between.80 and.60. So 20% to 40% of cooling is by moisture removal. Low S/T = greater dehumidification CBX32MV-036 AHRI Rating Point
A Balancing Act Most of the time: SHR > S/T …and this is good, excess moisture is removed! If SHR < S/T, then the indoor humidity will rise.
Design: Using ACCA Manual J load calculations (“Design Conditions”) for a Tampa house, we looked at the impact of a design change to reduce the sensible load. The SHR shifts down from.82 to.77 when, in this case, low-e glass was substituted.
Design: The SHR and equipment S/T are still pretty well matched – no problem. But…when it cools off outside: the latent load doesn’t necessarily drop-off like the sensible does!
The potential problem: On a Tampa “Dehumidification Design Day” the SHR difference between these two construction scenarios goes from.62 to.49. At.62 SHR, a conventional AC system, will just manage (indoor RH a little over 60%). With a.49 SHR, the same AC system will allow the indoor RH to drift up, uncontrolled.
Starting with the easiest: 1. Make sure ventilation is “just meeting” ASHRAE 62.2 2. Use “AUTO” fan mode (not “FAN ON”) 3. Don’t use a fan overrun timer. 4. Use lower indoor airflow rate (325-350 cfm/ton) 5. Select and condenser/coil combination with low S/T. These practices should be second nature in Florida, but they will be critical in the future. Options for Humidity Control (cont.)
The next easiest (adds to the equipment cost, but will help reduce the number of cooling season hours above 55% RH) 6. Use a modern thermostat, with humidity sensing capability, to: Select a low fan speed when there is excess humidity Allow a few degrees (2 to 4F) of overcooling when there is excess humidity 7. Use an air handler with a highly-efficient variable speed fan in conjunction with above control system (this is for efficiency reasons) Options for Humidity Control (cont.)
The option #6 + #7 has been reported on by Henderson and Shirey*. They found that, for a very high-efficiency home in Miami, the 1500 hours(!) of indoor RH above 60% was reduced by about 1/3. The point is that the #6 + #7 upgrade will not be sufficient for the most “efficient” home designs. *Closing the Gap: Getting Full Performance from Residential Central Air Conditioners, April 27, 2007; Henderson, Hugh and Shirey, Don Options for Humidity Control (cont.)
The last group can greatly reduce the incidence of excess humidity: 8. Install an integrated air conditioning and dehumidification system. Includes components of #6 and #7, but has an new operating mode with S/T ratio below.4, when needed. …or… Options for Humidity Control (cont.)
9. Install a high efficiency*, ducted-type dehumidifier to operate with the air handler to dehumidify the entire home. Options for Humidity Control (cont.) *A few dehumidifiers can perform this function with minimal “energy penalty” (still 13% to 33% see Henderson and Shirey, ibid.) Look for a high ENERGY FACTOR rating! Our company sells all of these systems.
Summary of Performance A seasonal simulation of the 1641 sq. ft. Tampa home (with single-pane windows and then with low-e windows), gave these humidity control results:
Conclusions In hot & humid climates, conserving energy while maintaining a comfortable and healthy indoor environment is going to be a challenge. Low sensible-load homes will require more sophisticated and expensive systems. The designers of homes, including the mechanical sub-systems, must be knowledgeable…or there will be problems. (Use the Dehumidification Design Day as another design point?)
Conclusions (cont.) Our national standards benefit consumers by making a large uniform market for companies to compete in. Regional efficiency standards would fracture that market and increase non-value-added costs. Manufacturers of residential HVAC equipment already provide diverse and comprehensive equipment solutions to handle most any application. Changes in home construction continually spur innovation in the HVAC industry, as companies seek competitive advantage.