Comments on: Warning: Skipping This Step with New HVAC Systems Can Lead to Misery

By: Cameron Taylor

Cameron Taylor — Fri, 06 Sep 2013 23:50:57 +0000

Perhaps some "book smart
Perhaps some "book smart" people have developed a measure of disconnect from the "real world smart" realm, but not the ones I know.

So let's look at Greg's alphabet bullet list:

A) If the system was designed from the beginning to maintain a house at 70 degrees indoors with 100 degree outdoor ambients, it's not oversized for those particular days. The rest of the time, it is, as is every other residential HVAC system operating under less than design conditions.
Poor maintenance habits are no excuse to oversize. In the case of neglected filters, all you have is more surface area on the evap that can freeze up.

B) People who spend hundreds of thousands of dollars on a house...how many hundred thousands? 100? They expect comfort at that level, but also energy efficiency. 1,000 hundred? Depends. Some with that much cash don't care, and build a monstrocity with high glazing to square foot ratios. Others do care, because they became wealthy by not being foolish in how money is spent.

C) So, the homeowner pays for and operates equipment designed for events that happen - what - how often? And the rest of the time it's oversized unless it's a design day.

D) "Standard" HVAC design conditions are based on a consensus of comfort developed by ASHRAE and ACCA. If your clients define comfort cooler or warmer than that, nothing is stopping you from designing toward that end.

E) Any "energy guru" worth his or her salt knows that comfort and energy consumption are coincident. In fact, they may know that many homeowners pay too much for comfort, due to poorly designed HVAC systems (and they may also know how to design AND install it properly).

F) Poor design and poor installation render poor results. That's real world, also.

By: Allison Bailes

Allison Bailes — Fri, 06 Sep 2013 18:58:44 +0000

Greg: I
Greg: I just checked out your website and, although your comment makes it sound like you're 'real world smart' HVAC contractor, you seem to be one of those 'energy geniuses' who does energy audits.

By they way, since you're in Austin, maybe you'd be interested in this other recent article I wrote about air conditioning in your great city:

Are You Making These Mistakes with Your Garage?

Also, you might be interested in attending ACCA's Building Performance Forum. I'm giving the opening keynote speech.

By: Allison Bailes

Allison Bailes — Fri, 06 Sep 2013 18:46:57 +0000

Greg:
Greg: Based on your comment, it looks like maybe you read the first couple of paragraphs only because you haven't addressed the main point of the article at all. If you can calm down a bit, stop assuming you know what I think, and read the whole article, you may be surprised to find out how much we actually agree.

By: Greg

Greg — Fri, 06 Sep 2013 18:16:55 +0000

This is the perfect example
This is the perfect example of book smart and real world smart. Most HVAC contractors fortunately excel at the latter while only some energy auditors excel at the first.

A: You assume A/C's always run at 100% efficiency. Real world: Homeowners don't replace filters when needed, may want their house to be 70 when it's 110 outside and have every right to, and have there A/C serviced only when there is a problem.
B: People that spend hundreds of thousands on a house put comfort above efficiency. I know, big shocker.
C: If you have 10 people over for a party, what are you supposed to do when your A/C isn't designed for that? Let them all sweat it out in the name of KWH's?
D: Every occupant is different in the real world, but when you are a book smart energy guru that isn't the case, you have a "standard" occupant.
E: Many HVAC contractors have serviced and installed thousands of units, believe it or not, they know what is best, yet are looked down upon by todays new wave of "energy geniuses" that have never had to worry about customer being comfortable and your businesses name being tied to that happy customers.
F: A high performance house is like a high performance car, makes no difference if the driver sucks.
Welcome to the real world.

By: Bob

Bob — Sat, 24 Aug 2013 23:38:44 +0000

Rheem has the market when it
Rheem has the market when it comes to 80% furnaces with high CFM x13 ECM motors. No other manufacture offers a 50K furnace with a 1600CFM blower. Perfect for southern climates where a 90% furnace doesn’t make sense and 50k is plenty of heat.

http://www.rheem.com/documents/rgpt-specification-sheets

By: Bob

Bob — Sat, 24 Aug 2013 23:33:16 +0000

http://acrightsize.com/files
http://acrightsize.com/files/7_reasons_why_oversizing_is_a_bad_idea.pdf 

http://acrightsize.com/files/10_reasons_why_oversizing_persists.pdf

By: Allison Bailes

Allison Bailes — Thu, 22 Aug 2013 00:38:28 +0000

John S.:
John S.: You're absolutely right. Not sure what was going through my brain when I wrote that, but I really did learn the continuity equation (A1*v1 = A2*v2) in intro physics, so I should've known better. I was wrong.

For those who want to know a little more about the continuity equation for fluids, here you go:

Fluid Flow and the Continuity Equation

By: John Semmelhack

John Semmelhack — Thu, 22 Aug 2013 00:19:58 +0000

Allison,

Allison,

I would argue that throw is a function of velocity leaving the register along with register design/shape and location....and has nothing to do with external static pressure.

High ESP does not necessarily equal long throws. Low ESP does not necessarily equal short throws.

Theoretically you could have extremely low external static pressure (by using aerodynamic fittings, low velocity/large-ish ducts and short runs) and use the register to increase the velocity of the airflow as it leaves the system....giving you the desired throw.

By: Allison Bailes

Allison Bailes — Wed, 21 Aug 2013 19:27:52 +0000
Michael C.
Michael C.: As both John S. and Jeffrey S. mentioned already, the garbage bag method is your least expensive option and is surprisingly accurate if you do it right. For exhaust fans, use the exhaust fan flow meter from the Energy Conservatory. See my article on bath fans in ENERGY STAR homes for details: This Little Hitch Snares ENERGY STAR Homes.

Armando: We can certainly debate what the threshold should be, but in my book, 1000 sf/ton is where you can start to think about a home being high performing. It certainly doesn't guarantee it, and we can easily do better.

M. Johnson: Absolutely. Using more expensive equipment can be better, but it doesn't absolve you from having to commission the ducts in my book. An ECM blower attached to a restrictive duct system will use more energy than a PSC motor.

Mike M.: Great advice. I wasn't aware of the TXV issue, so thanks.

Debbie: HVAC companies selling a 5 ton, 2 stage AC for a house that really needs only 3 tons are copping out at best, upselling just because they can at worst.

John S.: My point there was that you can get a really low sp by removing the ducts. Also, if it's too low, the throw might be really poor. I know David Butler says that throw isn't as important in high performance homes, but it's still somewhat important, especially if all the supplies and returns are in the same plane (floor or ceiling).

Jeffrey S.: Uh huh. I told you guys when I left that you might get stranded. Good thing you didn't have to walk back to the hotel, like poor Danko did at 4 in the morning.

By: Last shuttle sometimes means last shuttle

Tue, 20 Aug 2013 05:22:18 +0000
Jeffrey,

Jeffrey,

My IPad is now sprayed with milk, thanks to your message. And had it not been for those darn flip flops of yours, I really think we could've made it. :-)

Great times- send me your email so we can keep in touch!

Mike

Comments on: Warning: Skipping This Step with New HVAC Systems Can Lead to Misery

By: Cameron Taylor

By: Allison Bailes

By: Allison Bailes

By: Greg

By: Bob

By: Bob

By: Allison Bailes

By: John Semmelhack

By: Allison Bailes

By: Last shuttle sometimes means last shuttle