4 or 5 ton systems should be multi-stage...

Despite the passing of Regional Efficiency Standards, International Code requirements for Load Calculations and Equipment Selection, tighter homes and duct systems, I cannot see the likelihood of grossly over-sized equipment going down!  The significant problem at hand is that HVAC Contractors are either going to use the system design process, or not.  

In the meantime, Regional Standards are pushing Manufacturers into finding ways to make their systems more efficient.  Other than variable refrigerant flow (VRF), I am not sure what a manufacturer can do to increase the Energy Efficiency Ratio (EER).  In fact, some manufacturers and distributors have reported their variable capacity systems have actually tested, in a laboratory, lower EER than their two-stage and even single-stage counterparts.  We have seen the increased use of Electronic Expansion Valves (EEV) to maintain the lowest possible superheats in the industry.  Even increasing the physical size of Evaporator and Condenser coils in attempts to pick up/reject more heat.  This is all putting the burden on the contractor to find the room for installation, as well as finding systems that can deliver the latent capacity needed in the replacement market.

     So, I propose this: Why don't we require any 4 or 5 ton system be multiple stage or variable capacity?  This can address the significant over-sizing issue so often seen in the HVAC Industry.  After all, a study completed in 2006 by the Florida Solar Energy Center: "Measured Impacts of Proper Air Conditioning Sizing..." found little electrical savings for homeowners when replacing systems 47 - 65% oversized.  There is still significant peak energy savings to Electric Providers, hence the enforcement of proper sizing with most Utility Rebate Programs.  I wonder what those savings to the homeowner would have been if they just installed a multi or variable capacity system?  This code enhancement could change the industry significantly in future years, keeping the focus away from bigger coils and higher efficiency, but still pushing the contractor to proper sizing and equipment commissioning.  Yes, two-stage equipment costs more!  So you should size the equipment correctly to avoid these extra costs, increasing your bids.  Trust me, I have inspected as much as hundreds of A/C installations a year, for almost five years now, in a local utility rebate program.  Almost never do I see an installation or replacement system larger than a 3-ton.  Less than 10% of my inspected systems are larger, and almost always multi or variable capacity.  Customers still report increased comfort and reduced energy use.  Let's push efficiency using correctly sized, multiple capacity for the 4 or 5 ton systems, not physically larger units!

Views: 284

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Comment by Dennis Heidner on December 6, 2013 at 12:35am

The FSEC studies are good,  but using a 2006 study seven or eight years later when newer technology exists and had not been factored into the older study - may add some bias.

Did you really mean "keeping the focus away from bigger coils and higher efficiency"   right sizing the capacity should not mean downsizing the efficiency.  You really want the right capacity with the most efficient unit if you are trying to maximize the energy reductions.  If the point is to optimize the cost - unfortunately that might mean to oversize the system...(cheapest system). and then quickly sell and move out of the house :-)

Comment by Bob Blanchette on December 5, 2013 at 6:45pm

I question the study of replacing the oversized systems. Often ductwork is WAY too small and the oversized systems is not delivering it's rated capacity. Putting in a smaller unit matches the smaller ductwork better, and the savings are more significant than the study shows.

Comment by Christopher Morin on December 5, 2013 at 6:04pm
Thanks Bob! I couldn't agree with you more! If you need a furnace that big, you should probably zone with equipment or fix the envelope...
Comment by Bob Blanchette on December 5, 2013 at 5:42pm

While we're at it lets quit doing furnaces over 80k. Very few regions of the country require a furnace over 80k, most regions can go with a 40-60k in all but the largest homes. Yet 80-100k furnaces are routinely installed when heat less is 1/2 to 1/3 of that. High limits trip, heat exchangers crack, customer complain about wide temperature fluctuations.

Don't get me started on ductwork that rarely delivers the the high BTU performance of these monster sized HVAC units !!

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Kaushal Bharath Raju posted a discussion

Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.

We have a small 1940s single level house (1005sqf) in Berkeley, California that is in need of a…See More
5 hours ago
Christopher Morin posted a blog post

5 Things New Energy Efficiency HVAC Contractors Need to Know

1. Do not sell on Price! Use 'Simple Payback'The price of High-efficient equipment will undoubtedly…See More
10 hours ago
David Eggleton commented on David Eggleton's group Considering Permaculture &/or Transition
"In August 2014, in Minnesota, there's another unprecedented opportunity to meet and mix with a…"
16 hours ago
Glen Gallo commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"Nate, RE: Duct test On my own home and a rental I have tested more than once over the last many…"
17 hours ago
Profile Iconangela hines and Charles Goldman joined Home Energy Pros
21 hours ago
Jeff Flaherty joined Diane Chojnowski's group
Thumbnail

Tools of the Trade

A hammer and a saw used to be the key tools for home contractors. Today, the best-in-breed also use…See More
yesterday
Jeff Flaherty joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
yesterday
Debra Little joined David Eggleton's group
Thumbnail

Considering Permaculture &/or Transition

Some who work to increase energy efficiency and intelligent/wise use of energy are, and some will…See More
yesterday
Jim Gunshinan commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"Thanks for all the comments. Yes, it is interesting how the duct leakage grew over the years. Maybe…"
yesterday
Ed Minch commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"What sort of energy bill do you have now, what is  your target bill, and what will it cost to…"
yesterday
Nate Adams commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"I look forward to hearing more about the inside of the program! The big question that came to mind…"
yesterday
Glen Gallo commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"It is curious to see a 15% difference in the duct test from the test out of 2007 to the current…"
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service