HVAC is all About Air!

For decades the residential environmental air conditioning community has delivered a less than stellar performance on installed quality. The HVAC industry suffers the stigma, not from intentional wrong doing, but rather adoption of rules of thumb that have little basis in fact for the industry. Prove to the industry they are on the wrong path and they will adopt right thinking. The “Home Performance”, “House as a System” model is being accepted across the country with great success when marketed correctly. We must remember our industry in hot humid climates began only in the mid 1960’s in great numbers.
The path the industry took in past years is understandable. While meeting housing demand for the sheer numbers of Baby Boomers and a higher standard of living, engineering values were sidestepped with shortcuts. With cheap energy prices no one was the wiser. As energy prices began to rise and with the oil embargo of the late 1970’s it became apparent a more efficient housing stock had to be developed. Once a path was established to improve construction methods the emphasis would shift to higher performance HVAC equipment. In the wake of this rapid demand and an importance on equipment development, shortcuts on materials and installation methodology again took over the industry. As a result questions were asked;
• Manufacturers questioned warranty part returns that fail prematurely with little reason.
• Green Energy gurus scratched their heads when efficiently built homes fail to perform at acceptable comfort levels.
• Contractors ponder why some systems just operate poorly for no apparent reason.
Since 2005 we have been advocates for more study of delivered efficiency at the interior of the home.
As a result in 2011 we began using ideas developed we might be able to impact air delivery systems with minimal expense and improved performance.
We have discovered our ideas are working and to date is extremely encouraging. Our customers are impressed with the results for quite, comfortable and efficient environmental home air conditioning systems. The ideas we came up with are simply a rediscovery of what the HVAC industry practiced in its infancy. Below is the blueprint we use to achieve great results.
Proper appliance set up-
We find well over half the systems we visit are set up improperly. Incorrect fan speeds selected on standard blower motors. Timed on and off fan operation (for harvesting evaporator energy) was left at factory defaults. There were incorrect fan settings on variable capacity equipment. Thermostats for high-end equipment were left at default programs in selectable fields.

Size up the system prior to proposing repairs-
Where several studies across our country have proven over 80% of systems are oversized and deliver only 60% of rated capacity shouldn’t we propose lasting improvements. There are methods to identify the issues quickly. The opportunity for improvement should be given the homeowner. Failure to inform only perpetuates problems in the HVAC industry.

Static Pressure Monitoring-
We should begin taking static pressure upon arrival at a residence. This practice should take precedence over hooking up gauges. In almost every home we visit static pressure is a persistent issue. Rules of thumb on static pressure should be avoided. Refer to manufacturer specifications and work to obtain the required static. The industry engineers who design the equipment know what system output is required. If we short cut static pressure requirements with generic information we need forget static pressure all together.

Deltas-
Temperatures can identify issues early however don’t be fooled. A Delta T without air flow requirements validated can lead us down a meaningless path. This is similar to super heat and sub cooling. Without verified air flow present, readings are bogus.

Return air adequacy-
Return air continues to challenge our industry. We continue to follow a trend of increased return air size to provide adequate flow for our systems. This includes a practice of increasing filter area. Seldom will systems of three-ton (nominal size) or larger perform with only one high-efficiency air filter. Some systems require commercial grade returns to obtain flows while others (platform return) may need extensive alteration.

Supply plenum design criteria-
Substantial gains in air flow performance and comfort can be achieved with simple changes in plenum design. These include increased plenum length to accommodate air stabilization off the blower, a pressure rebound zone and adequate take off surface. We must also include more efficient transitions when installing evaporator or adapting existing plenum and duct work. We see great gains by avoiding taps at specific areas of the plenum formerly utilized without hesitation.

Duct design and proper installation-
Duct flows and their performance have been over rated for quite some time. New duct performance flow criteria are available through a few sources. Even more important than equipment selection is the fact actual duct installation quality will determine performance outcomes. We must pay attention to air duct installation.

Terminal device use-
Very little attention is paid to grill location and the type of grill used. We find same size grills with differing manufacturers flowing up of 20 percent more air. Some homes have been fixed with only grill replacement. With homes in hot and humid climate it is extremely important to avoid air delivery to exterior wall at velocities above fifty feet per minute. During mild weather the practice can cause condensation and deterioration of construction material.

In the U.S. the over arching goal has been to weatherize the structure by sealing the envelope and adding insulation. With fewer homes without central air conditioning on in the market each year the need to adopt a change becomes more apparent. We need to provide sustainability through a process of fixing the air delivery system, and then sealing the envelope and adding insulation. Fixing the air delivery system later only calls for additional weatherization measures to be repeated. Consumers will be slow to accept the idea. After all “we put the air conditioning in”. There must me an honest effort to advance an approach to inform the home owner so an intelligent decision can be made on possibly their most valuable investment.
In conclusion poor system performance in the new and retrofit market left unaltered, costs everyone. Obviously it costs the consumer in higher utility bills poor comfort and premature replacement. It cost manufacturers with increased warranty and lost wholesale revenue. It costs the contracting community with poor customer retention and lost revenue when servicing call backs for both service and retail sales.
Most importantly we can answer the question of “how do we get the install right?”