Duct leakage in cooling loads

[jimj]

However, when the duct leakage test is performed with a blower door using the subtraction method, isn't that done at cfm50?

be.

Yes it is, cfm50 when doing the subtraction method with the blower door.

[energy_rater_La]

cool air,
my point was that here in Louisiana
our program tests both house and ducts @50Pa.
with ductblaster.
this is one of the rules for our program.

if subtraction method was
allowed, it would be..for us..still 50pa.

I haven't had time to read the post pstu..
maybe over the weekend.

[jimj]

Will the duct blaster measure duct leakage properly at 50pa? Not saying it won't just never done it.

[catmanacman]

performed duct leak test with flow hood on many duct systems mostly duct board and flex and found plenty of them leaking 25 percent and more but most were in the 15 to 20 percent range after repairs less than3 percent, also found sheet metal duct systems that leaked in the 15 percent range . think about it paying to cool the air than through away 1/5 of it or 1/4 of it also when your duct system does not leak your filters stay clean longer duct sealing can and will save money

[energy_rater_La]

jim..beats me. I think that the state just wanted to make processing the ratings
standardized. like setting rate statewide for utility costs @ 9 cents per kwh when it actually fluctuates. some small towns have their own utilities and cost is .18 per kwh,
lowest is my co-op @ .08 and the two largest utility providers are .14 cents per kwh.
our software (remrate) allows us to change these rates to provide actual savings,
but to submit to the state we have to use their numbers.

for me..it isn't a big deal if the duct leakage is off a little.
I think folks get too distracted by that minimal percentage.
the fact is if the system provides 2000 cfm and only 1500
is actually delivered then what does it matter if its 1550
or 1450? you still have unacceptable duct leakage.

in my world its more important to find the leakage and fix it.
our program mandates 5% Energy Star 10%.
it is difficult to seal to 5% in existing homes.
I've taken duct systems and returns apart and put them
back together sealing everything..including equipment leakage
and never gotten less than 5%.

an average is 25-30% for flex. sheetmetal ducts higher due to more
seams & joints. harder to seal. but with a lot of time and effort
it can be done. just delays wrapping ducts until mastic dries.

keep in mind that probably 80% of our duct systems are in the attic.
15% in crawlspaces and 5% in conditioned space.
the % of ducts in conditioned space is changing with the advent of
foam insulating the rooflines.

[jimj]

for me..it isn't a big deal if the duct leakage is off a little.
I think folks get too distracted by that minimal percentage.
the fact is if the system provides 2000 cfm and only 1500
is actually delivered then what does it matter if its 1550
or 1450? you still have unacceptable duct leakage.

Yup you got it!

keep in mind that probably 80% of our duct systems are in the attic.
15% in crawlspaces and 5% in conditioned space.
the % of ducts in conditioned space is changing with the advent of
foam insulating the rooflines.

People are truly becoming educated and concerned about energy costs ( at least some are) and are asking questions. Unfortunately most in the HVAC industry have no clue!

We started up two Energy Star Home systems ( 3.0) today, both foam homes. I know the homeowners will not believe how quiet and comfortable there new homes will be.

[Cool_Air]

cool air,
my point was that here in Louisiana
our program tests both house and ducts @50Pa.
with ductblaster.
this is one of the rules for our program.

if subtraction method was
allowed, it would be..for us..still 50pa.

I haven't had time to read the post pstu..
maybe over the weekend.

Thanks I understand.

[adamwhatley]

I have always used Remrate to size homes out over the years. I have tried all load programs and all are pretty much the same. With that said Manual J and wright soft are up there with Remrate to me. Wright soft software in my opion over sizes by 1/2 ton unless everything is perfect. Manual J is spot on when it is done right but very time comsuming. Remrate to me is easy to use but I was taught on it through the same Energy Program that LA Energy Rater has and is working with.


As far a duct leakage goes I do belive that uses good Margins but need to watch your blower door results and factor into the load along with air filtration along with all the other important sizing things that our homes have.

[Cool_Air]

cool air,
my point was that here in Louisiana
our program tests both house and ducts @50Pa.
with ductblaster.
this is one of the rules for our program.

if subtraction method was
allowed, it would be..for us..still 50pa.

I haven't had time to read the post pstu..
maybe over the weekend.

thanks

[r-290]

FWIW here in California we can have up to 15% duct leakage with a system change out. If new ducts were put in then that number drops to 6%.
So duct work in the attic and loses of 50% total energy is not far fetched.
as Lynn pointed out in the DOE doc.

I'm sure in the next few years foil flex will be the only thing allowed in attic's

[energy_rater_La]

so even in a change out you address duct leakage? thats pretty good.
wish we had that kind of enforcement here.

[pstu]

The original paper sure seemed to say 86 CFM was the average duct leakage for the Houston area homes. Houston homes built in the last decade are not small, and it could be reasonably estimated the average AC size is about 5 tons -- that would be 3-5% duct leakage would it not? I find it hard to believe Houston area homes are constructed with this degree of craftsmanship.

If this is not the straight up honest truth, then I would be interested to understand what data would allow a professional organization to say this. Scuttlebutt about the Centerpoint Energy marketing department is they are hardly committed to the truth, but the partner Advanced Energy looks like it has a reputation to uphold.

-- Pstu

[r-290]

Makes those mini splits better and better all the time

[energy star]

From what a read California has a third party inspection on almost all HVAC work (title 24 and whatever else) that is being done in a home. I like it.

[lynn comstock]

From what a read California has a third party inspection on almost all HVAC work (title 24 and whatever else) that is being done in a home. I like it.

New construction gets inspected when there is a water and electrical hookup.
In our area (AZ) most replacement equipment is not inspected because contractors do not get permits. I imagine that this is true in most jurisdictions. Code doesn't mean anything when it is not enforced.

[energy_rater_La]

Code doesn't mean anything when it is not enforced.
which is often the case in my area. in the cities there is
enforcement, but in the rural areas it is spotty at best.

often the code inspectors pov don't agree.
code is dependent upon their interpertation of what it says.
all those shalls and musts don't always make it to the job site.

pstu..I find it hard to believe that 6% duct leakage is average anywhere.
but I'm a skeptic until I see it/ test it for myself.
I do know that it would have to be installers trained by same trainer
or same installers doing the sealing work on all projects.

and
"If this is not the straight up honest truth, then I would be interested to understand what data would allow a professional organization to say this. Scuttlebutt about the Centerpoint Energy marketing department is they are hardly committed to the truth, but the partner Advanced Energy looks like it has a reputation to uphold."

scuttlebut I get is that everyone a hedge factor. as utility programs begin to
influence the auditing business people need to be realistic about just how
much utility cost they want the average homeowner to save.
50% lol..more like 15-20% this is what I get from my co-op and one of the
two large utility provider's energy managers in my area.

[lynn comstock]

....people need to be realistic about just how much utility cost they want the average homeowner to save.
50% lol..more like 15-20% this is what I get from my co-op and one of the
two large utility provider's energy managers in my area.

It really depends on the peak load capacity of the utility. Cutting AC load reduces peak load and makes the utilities more profitable. Why? Because peak loading consumes the most expensive electricity as most of the time the equipment needed is on standby. Also, if peak demand grows, new power plants must be planned and constructed.

[r-290]

From what a read California has a third party inspection on almost all HVAC work (title 24 and whatever else) that is being done in a home. I like it.

Correct, the name Title 24 Building Energy Efficiency Standards is called title24 for short. It covers all type of home energy use from HVAC to windows to water heaters. Its updated every few years.

If you take out a permit it will be inspected by the building dept ( code compliant) and then you are subject to a HERS testing. Can't remember what HERS stands for, but just think Energy Rater. They will check the subcool level by connecting up there gauges to the condenser and check the liquid line temp. They check the fan watt draw and CFM flow. They run a duct blaster and check for leaks.

Like anything there are lot of rules and exceptions which is nice and a pain at the same time.

[r-290]

It really depends on the peak load capacity of the utility. Cutting AC load reduces peak load and makes the utilities more profitable. Why? Because peak loading consumes the most expensive electricity as most of the time the equipment needed is on standby. Also, if peak demand grows, new power plants must be planned and constructed.

So the power company's answer is Smart meters that charge you twice as much during peak time. Which is 10am to 8pm and they charge you double when you go over the base line of 700 kWh too.

[pstu]

It really depends on the peak load capacity of the utility. Cutting AC load reduces peak load and makes the utilities more profitable. Why? Because peak loading consumes the most expensive electricity as most of the time the equipment needed is on standby. Also, if peak demand grows, new power plants must be planned and constructed.

Another thing about the utility point of view, is usually a cut in residential demand (peak KW) goes hand in hand with a cut in energy (KWH). Since most utility tariffs are based simply on KWH, they have trouble wanting that. A very specific program to cut demand, with repayment from the utility commission for their "negawatts", would be a clear exception.

I know the Houston area utility invested in some programs to manage demand, and their request for repayment was rejected by the utility commission. So they may view conservation with some suspicion, at the top management level.

Regards -- Pstu