California's Official Mandatory 70F Return Air db

[Tommy Torero]

http://www.energy.ca.gov/title24/200...n_Protocol.pdf

Here's what I am up against out here in the land of fruits and nuts.We have an energy code so progressive it drives good contractors underground and honest contractors to pull what's left of their hair out.

A few choice comments that I'd like clarified:

A Return Air drybulb of 70F "was determined to be necessary to achieve reliable test results and to avoid the possibility of freezing the indoor coil and damaging the air conditioner."

We are required to add supplemental heat to the Return we call it the Blow-Dryer Method: "Electric resistance convection room heaters or hair dryers widely available with a 1,500 Watt capacity are suitable for use in a 110 Volt, 15 Amp circuit, of which there are likelyto be 4 or more in a dwelling. By use of extension cords, each heater can be plugged into a separate circuit." Does it matter that a 1500w blowdryer only delivers 75cfm of air?

"an air conditioner that produces a nominal 20°F temperature drop across the cooling coil, the addition of supplemental heat at the return grille that creates a 10°F temperature increase of the return airstream will counteract half of the air conditioner’s cooling capacity"

Figure 1. shows
Return air dry‐bulb temperature with no supplemental heating will drop from 75F to 60F in 30 minutes. If that was true I would only have to run my AC for a few minutes at a time.

This is the official document we must adhere to.

I am just a lackey trying to do my job and now I have to buy 4 blow-dryers?

What's your expert opinion?

Thanks!

[air2spare]

Isn't this a repost?

...and the requirement is 70 and above

[beenthere]

If thats what they want. Thats what you need to do.

[Tommy Torero]

If thats what they want. Thats what you need to do.

I understand that that is what I have to do but is it true....

a 10°F temperature increase of the return airstream will counteract half of the air conditioner’s cooling capacity?

a return temp below 70F can freeze the coil?

{I thought the coil had to be below 32F and low airflow and that a system with proper subcooling and superheat wouldn't freeze.}

and can I cool my house from 75 to 60F in 30 minutes?

I am trying to learn the science of AC and should I go around telling people less than 70F in your Return may ruin your system?

Thanks!

[amd]

{I thought the coil had to be below 32F and low airflow and that a system with proper subcooling and superheat wouldn't freeze.}

The temperature of the coil will always be far lower than the r/a temp.

Refrigerant saturation temp <=32F can cause the coil to freeze.

[jimj]

http://www.energy.ca.gov/title24/200...n_Protocol.pdf

Here's what I am up against out here in the land of fruits and nuts.We have an energy code so progressive it drives good contractors underground and honest contractors to pull what's left of their hair out.

A few choice comments that I'd like clarified:

A Return Air drybulb of 70F "was determined to be necessary to achieve reliable test results and to avoid the possibility of freezing the indoor coil and damaging the air conditioner."

We are required to add supplemental heat to the Return we call it the Blow-Dryer Method: "Electric resistance convection room heaters or hair dryers widely available with a 1,500 Watt capacity are suitable for use in a 110 Volt, 15 Amp circuit, of which there are likelyto be 4 or more in a dwelling. By use of extension cords, each heater can be plugged into a separate circuit." Does it matter that a 1500w blowdryer only delivers 75cfm of air?

"an air conditioner that produces a nominal 20°F temperature drop across the cooling coil, the addition of supplemental heat at the return grille that creates a 10°F temperature increase of the return airstream will counteract half of the air conditioner’s cooling capacity"

Figure 1. shows
Return air dry‐bulb temperature with no supplemental heating will drop from 75F to 60F in 30 minutes. If that was true I would only have to run my AC for a few minutes at a time.

This is the official document we must adhere to.

I am just a lackey trying to do my job and now I have to buy 4 blow-dryers?

What's your expert opinion?

Thanks!

I would come back in the spring as MOST manufactures recommend and do my FINAL charge.

[Tommy Torero]

I would come back in the spring as MOST manufactures recommend and do my FINAL charge.

thanks for your response jimj but by Spring as a special inspector I will have 600-900 refrigerant charge tests to do. This costs a contractor an average of $150/ea (tech time/HERS Rater) so.....waiting costs an extra $90,000 -$135,000

I still am looking for the truth that a 10°F temperature increase of the return airstream will counteract half of the air conditioner’s cooling capacity" it doesn't seem to pass the "smell" test and if a state agency is going to mandate something then they should offer more than just a "cause we said so!"

Don'tcha think?

-Tommy

[jimj]

thanks for your response jimj but by Spring as a special inspector I will have 600-900 refrigerant charge tests to do. This costs a contractor an average of $150/ea (tech time/HERS Rater) so.....waiting costs an extra $90,000 -$135,000

I still am looking for the truth that a 10°F temperature increase of the return airstream will counteract half of the air conditioner’s cooling capacity" it doesn't seem to pass the "smell" test and if a state agency is going to mandate something then they should offer more than just a "cause we said so!"

Don'tcha think?

-Tommy

6,000 watts will add 20,472 BTU's of load, so it will depend on your unit size IF that's half the systems load capacity.

[skippedover]

Sounds like nonsense to me. If a 75 degree house can be cooled to 60F in 30-minutes, I'd say the system is grossly oversized. If they wanted to do something truely progressive, they'd mandate 2-stage cooling for all. If there's an area (it's a big, big state) that has more stable temps but high humidity, then mandate a whole house dehumidifier.

You say you've got to check charge? That's done under load using super heat or subcooling, depending on the metering device. Why are they messing with return air temps? Makes no sense to me, at least the way you've presented it.

[Tommy Torero]

6,000 watts will add 20,472 BTU's of load, so it will depend on your unit size IF that's half the systems load capacity.

Thanks JimJ-

So does it matter that the 6000watts are being delivered by hair dryers that produce only 75cfm?

That's what is confusing me--- let's use 1 blow dryer @1500 watts = 5,118 BTU's and 75cfm

If I put my blow dryer near a Return grill on a 3 ton system (airflow 1200 in a perfect world)and shoot it in.... am I adding a "TRUE" 5118 BTU's or am I adding 75cfm of 5118 btus mixed with 1200cfm of return air?

That's where I lose it.

Thanks to all for your help.

Tommy

[Tommy Torero]

Sounds like nonsense to me. If a 75 degree house can be cooled to 60F in 30-minutes, I'd say the system is grossly oversized. If they wanted to do something truely progressive, they'd mandate 2-stage cooling for all. If there's an area (it's a big, big state) that has more stable temps but high humidity, then mandate a whole house dehumidifier.

You say you've got to check charge? That's done under load using super heat or subcooling, depending on the metering device. Why are they messing with return air temps? Makes no sense to me, at least the way you've presented it.

skippedover-

they are saying that a return air temp below 70 might freeze the coil and ruin the compressor. My wine store keeps it's bottles at 54F which means their Return probably gets as high as 56F..... they must be freezing their coil daily.... right?

Someone told me that that was the difference between "comfort cooling" and refrigeration... (although they both require superheat and subcooling.) I am just trying to learn what's true and what's BS.

thanks

[hvacrmedic]

thanks for your response jimj but by Spring as a special inspector I will have 600-900 refrigerant charge tests to do. This costs a contractor an average of $150/ea (tech time/HERS Rater) so.....waiting costs an extra $90,000 -$135,000

I still am looking for the truth that a 10°F temperature increase of the return airstream will counteract half of the air conditioner’s cooling capacity" it doesn't seem to pass the "smell" test and if a state agency is going to mandate something then they should offer more than just a "cause we said so!"

Don'tcha think?

-Tommy

4 1500 watt hair dryers or portable electric space heaters would produce a heating capacity of about 20,000 btu/hr. That's about half the capacity of a 3.5 ton system, and a more capacity than a 1.5 ton system. HTH.

[jimj]

Thanks JimJ-

So does it matter that the 6000watts are being delivered by hair dryers that produce only 75cfm?

That's what is confusing me--- let's use 1 blow dryer @1500 watts = 5,118 BTU's and 75cfm

If I put my blow dryer near a Return grill on a 3 ton system (airflow 1200 in a perfect world)and shoot it in.... am I adding a "TRUE" 5118 BTU's or am I adding 75cfm of 5118 btus mixed with 1200cfm of return air?

That's where I lose it.

Thanks to all for your help.

Tommy

Maybe this will help, sensible BTUH = cfm x TD x 1.08 ( at sea level)


75 cfm x 65 TD x 1.08 =5,265 BTUH sensible ( so whats the TD of your hair dryer?)