ASHRAE Performance Standards

[wward]

Anyone know what the performance standard is for cooling a home when outside temperatures are under 95F?
I know at 95F and above a 15 degree difference is acceptable.
Also, is the differential measured from return to plenum or outdoor verses indoor?
Thanks!

[David A. Andersen]

I know at 95F and above a 15 degree difference is acceptable.

Did ASHRAE publish that!?

If so, send it to me. I have some *** to chew...

95f is a design standard for only a few cities in the USA.

If you think 15 F db is any kind of "standard", someone is mistaken.

[wward]

This quote is taken directly from the warranty book our company provides to homeowners and uses it to hold builders to the performance standards during the first year of occupancy.


"Performance Standard:
Where air-conditioning is provided, the cooling system shall be capable of maintaining summer design conditions as specified in ASHRAE handbook. In case of outside temperatures exceeding 95 degrees F, a differential of 15 degrees F is acceptable. Federal, state, or local energy codes shall supersede this standard where such codes have been locally adopted."

I have ordered the 2008 ASHRAE handbook, but haven't received it yet.

[David A. Andersen]

Ah yes. That's under the section "HVAC/R for dummies"!

Seeing builders don't have the test equipment required and it is illegal for them to do anything else, that are playing the delta T game to see (after it is properly designed and installed) if they still are meeting performance standards.

I guess most Home Inspectors fall under this same criteria.

That is why I think this, about that!
http://www.midtninspections.com/blog?page=2

[Doug Edwards]

Dave,
Great article! Add one more point at the end. HVAC is the single most neglected piece of equipment / system in the home by the homeowner.

[Bruce M. Graham]

what RH does this "standard" maintain?

[David A. Andersen]

HVAC is the single most neglected piece of equipment / system in the home by the homeowner.

Agreed.
That is in my report and is the line I use when a client is trying to decide if they want a more extensive HVAC inspection (beyond turning it on at the thermostat as state law requires).

And when I get "it's new construction" or "they just put in a new hvac unit" it doesn't need inspecting...

.. oh really?

[wward]

Point made, I logged 189 hours in a tech school learning the basics of HVAC and refrigeration and have a universal refrigerant certification. I understant what your argument is.

I have a homeowner with a warranty on his system and claims it's not meeting the requirements " 20 temp difference from outsied to inside when outside temp is under 95 degrees" he is "elegedly" is quoting from the ASHRAE handbook and is demanding a bigger unit be installed at the cost of the builder.
Can't just give this guy the middle finger without going to court.
Builder had attic insulation inspected, GOOD
HVAC contractor inspected the system, GOOD
Power company even recorded indoor temps at an average of 74 degrees over an eight day period. Homeowner is still demanding a bigger unit.

All I wanted to know was is there a performance standard in the ASHRAE?

Guess I'll have to wait untill the book arrives.

[David A. Andersen]

So give it to him!

He can live in a cave with water dripping off the ceiling and his new friends "black mold" can come to live with him!

I when you get the ASHRAE handbook, look up the graph concerning comfort standards: (chapter 5 on psychrometrics and Chapter 6 psychrometric tables).

You will see (as posted below) that comfort levels can range from 72° to 80 agrees Fahrenheit and 19 to 72% relative humidity.


So as you can see you have an 8 degree Fahrenheit dry bulb temperature variance to start with...

This chart, in of itself proves that dry bulb temperature differentials are irrelevant when attempting to evaluating HVAC system design in accordance with dry bulb temperature differential.

[kluce]

When I started working for a large company that focused on residential I was going to HVAC school at the same time. I learned from the books plus the way the old timers have always charged units. I would check the freon levels (by the book) after they where done installing the units and found that as long as the outside temperature was above 70 degrees, these old timers were ending up charging them within +/- 3 psi of the pressure I got using the super heat method. After working with them for a while, I learned how to check the charge with my hand on the suction line, know if the outside unit is dirty by touch the liquid line, check the Freon charge by looking at the temp on the Freon gauge plus a lot more other methods.

I just don't see what the issue is. You check to see if the outside unit is dirty, check to make sure everything is running, check the inside air filter and take a dry bulb temperature drop. If the number comes back higher or lower than what is expected, then that home inspector refers the buyer to a HVAC tech. Out of all the split system units I have worked on/inspected, I never had a call back wondering why I called out the Temperature drop being too low or too high.

While I agree that a properly done dry bulb temperature drop by itself is not the best way of doing things, it does give us an idea if a problem exists.

David A. Andersen
This chart, in of itself proves that dry bulb temperature differentials are irrelevant when attempting to evaluating HVAC system design in accordance with dry bulb temperature differential.

I don't evaluate HVAC system design (Ok, I do, but only it's basic components). I mainly focus on its basic performance.

I know people disagree with me on this but this has been my experience as a HVAC tech for 12 years and a full time home inspector for 10 years.

[Dale Duffy]

Originally Posted by dedwards

Dave,
Great article! Add one more point at the end. HVAC is the single most neglected piece of equipment / system in the home by the homeowner.

Exactly Doug...I will be adding that comment you made which is VERY TRUE to all my inspection reports from now on....Thanks for the idea..!!

Besides the "Have the system serviced NOW", which I already state in just about EVERY inspection Report, I will add your great comment...."The HVAC System is the most neglected piece of equipment / system in a Home"...!!...and I truly believe it is to, in 99.9% of ALL homes.

I can't count the number of times I have removed the panel covers of Heat Pumps and found burnt connections at several locations, vibrating through the years, conductors become loose, things burn up, fail...all from lack of regular maintenance..!!!

[Bruce M. Graham]

Back in the HVAC Tech days, we called that breakdown maintenance. No body has the money for a preventitive maintenance program, which I also recommend on all of my reports, but they were always able to come up with more $$$$ to get it fixed when it broke, go figure.