As I had brought up years ago, ACCA's Manual S was in dire need of an update.  Written in 1995, Manual S Residential Equipment Selection was passed by with huge technical and efficiency strides within the HVAC industry.  Think about it: ECM Motors were in their infancy, condensing furnaces were still prone to failures, and variable refrigerant flow was far from mainstream in the U.S.  All addressed in the updated Manual S! I have to say, their committee did a thorough job addressing updates to a process that is essential to system design and a code requirement in most of our country!  I highly recommend HVAC Sales Staff, System Designers, and Building Analysts purchase a copy of the new text, but in the meantime here is a teaser:

1.  Multi-Stage Central A/C: can be sized between .90 and 1.20 of the total building load.  This additional 5% of capacity vs. 1995 becomes increasingly important as homes get tighter and Sensible Heat Ratios rise.  Higher airflow to handle the increase in sensible loads lends to higher capacities.

2.  Variable Capacity Central A/C: can be sized between .90 and 1.30 of the total load.  See #1 for sensible capacity reasons, but variable capacity equipment is great for handling high latent capacities when operating on part load days as well.

3.  Cold Climate Heat-Pumps: can be sized to the total cooling building load + 15,000 btu/hr maximum.  This goes for single-stage, two-stage, and variable capacity equipment.  For mini-split heat-pumps, this 15K is above the total block load.

4.  Heat Pump Supplemental Electric Heaters: can be no larger than 5KW if the heat load is < 15,000 btu/hr.

5.  Fossil Fuel Burning Furnaces and Boilers: can be sized between 1.0 and 1.40 of the total heat load.  Ok, this isn't a change, just thought it was important to know!  If installing a furnace that needs a larger blower for cooling, maximum is now 2.0.

     Loaded with up to date examples, the new Manual S is far from a dust collector.  A great reference manual, but lets just hope it is not for another two decades like it's predecessor...but don't take my word for it!

Excess Air

Views: 81

Comment

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

Join Home Energy Pros

Comment by Eric Kjelshus on August 28, 2014 at 8:33am

I run loads each day.  BUT my completion does not,    I see so much over sizing  last job was needing 34,000 and he put in 120,000 BTU's ( the box fit)  I took out 1/2 the burners so the BTU fit the duct work and closer to the building.    My grand Pa would size 3 times needed or down to -40  so you could open the windows in bedrooms 8" to get "air" at night.   in the 1880 the gas was made from coal and was very high CO  when would burn,  some  Lights would be gas and CO in the building go high so would open window's to vent the home.    Gas was so cheap that was not metered  just so much a yr.

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

Aaren Stewart posted a discussion

Let's solve this HVAC quiz!!!

Answer these three simple problems of your HVAC systems, let's see how much you know your system…See More
6 hours ago
Chris Laumer-Giddens posted a blog post

Mini-Split Heat Pumps are Quirky, Especially their Capacity

Mini-Split Heat Pumps are Quirky and Still EffectiveThe name "mini-splits" generally refers to heat…See More
15 hours ago
Jan Green posted an event

Solar Course for Appraisers at SRP's Pera Club

November 13, 2014 to November 14, 2014
"As the US continues to search for energy alternatives, properties improved with solar PV…See More
15 hours ago
Hal Skinner replied to Hal Skinner's discussion What an RCC can do with no R- insulation in the walls.
"Just like paint.  RFoller and brush or strong airless sprayer.  It has the consistency of…"
18 hours ago
Hal Skinner replied to Hal Skinner's discussion What an RCC can do with no R- insulation in the walls.
"ty and thermal emission leveld of many materials including bricks and white paint.  They do…"
19 hours ago
Hal Skinner added a discussion to the group The RCC Classroom (Radiant Control Coatings)
Thumbnail

Walmart goes green in Texas

We applied cour RCC to 5 Walmart superstores in Texas.  Worked great and they wanted it.  Then they…See More
19 hours ago
Kim Tanner replied to Trip Smith's discussion Where to spend my marketing dollars?
"Direct mail doesn't do very much, in my opinion, unless you have awesome coupons! Honestly,…"
19 hours ago
Hal Skinner replied to Hal Skinner's discussion What an RCC can do with no R- insulation in the walls.
"Mornn Trip and Bud, In this case all I can do is report it exactly as it was told to me.  I…"
20 hours ago

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service