Need your expertise

Posted by The King on February 20, 2009, 3:55 pm

>The unit ran fairly quiet until recently. I'll take a video tomorrow
>and upload to youtube.
>Here's what I've checked out:
>Airflow check using 5 KW aux heater strip w/o heat pump:
>Air handler tested w/ ACTUAL measured voltage/current to strip:
>237 VAC / 20.0 A = 4.74 KW
>CFM = KW X 3514 X 1.08 / TR
>Hi speed: 19 F temp rise 74 to 93 = 947 CFM
>Mid speed: 21 F temp rise 72 to 93 = 857 CFM

I hate to break it to ya Jeanuis but your calculations are wrong.

BTUH = I X E X 3.412

20a x 237v x 3.412 = 16172.88 BTUH

CFM = BTUH / temp rise X 1.08 @ sea level. The constant, 1.08 drops
slightly with altitude.

19 x 1.08 = 20.52
16172.88 / 20.52 = 788.15 CFM on high speed.

16172.88 BTUH is electric heat not mechanical refrigeration BTUH.

>Heat pump (about 40 F outdoor temp) w/o heat strip:
>BTU = CFM x TR / 1.08
>Using 856 CFM I came to 20,631 BTU for temp rise 72 to 98

Posted by Jean on February 20, 2009, 4:55 pm

On Fri, 20 Feb 2009 15:55:01 -0500, The King

>>The unit ran fairly quiet until recently. I'll take a video tomorrow
>>and upload to youtube.
>>Here's what I've checked out:
>>Airflow check using 5 KW aux heater strip w/o heat pump:
>>Air handler tested w/ ACTUAL measured voltage/current to strip:
>>237 VAC / 20.0 A = 4.74 KW
>>CFM = KW X 3514 X 1.08 / TR
>>Hi speed: 19 F temp rise 74 to 93 = 947 CFM
>>Mid speed: 21 F temp rise 72 to 93 = 857 CFM

>I hate to break it to ya Jeanuis but your calculations are wrong.

I agree. But your calculations are also wrong so there is no need for
insults.

I am not the HVAC expert. That is why I'm asking questions in this ng.

>BTUH = I X E X 3.412
>20a x 237v x 3.412 = 16172.88 BTUH
>CFM = BTUH / temp rise X 1.08 @ sea level. The constant, 1.08 drops
>slightly with altitude.

Your formula doesn't agree with mine....

>19 x 1.08 = 20.52
>16172.88 / 20.52 = 788.15 CFM on high speed.

I've gone back to check my original formula:

At sea level (I can walk to the beach):

TR = kW x 3412 x 1.08 / CFM

(cross multiply to get CFM)

CFM = kW x 3412 x 1.08 / TR

CFM = 20 x 237 x 3412 x 1.08 / TR
CFM = 4.74 x 3412 x 1.08 / TR
CFM = 17466.7104 / TR

Therefore:

@ 21 F temp rise (mid-speed)
CFM = 17466.7104 / 21 = 831.75

@ 19 F temp rise (hi-speed)
CFM = 17466.7104 / 19 = 919.26

I've gone back to look at calculations I did back in Nov and these
agree.

Any comments?

>16172.88 BTUH is electric heat not mechanical refrigeration BTUH.

Thanks. That appears to be where I got the 3514 from. I don't know how
I slipped it into the formula for original CFM this time. I've been
taking a crash course in understanding HVAC so give me a break.

>>Heat pump (about 40 F outdoor temp) w/o heat strip:
>>BTU = CFM x TR / 1.08
>>Using 856 CFM I came to 20,631 BTU for temp rise 72 to 98

Is this correct?

Posted by Jean on February 20, 2009, 5:35 pm

>On Fri, 20 Feb 2009 15:55:01 -0500, The King

>>>The unit ran fairly quiet until recently. I'll take a video tomorrow
>>>and upload to youtube.
>>>Here's what I've checked out:
>>>Airflow check using 5 KW aux heater strip w/o heat pump:
>>>Air handler tested w/ ACTUAL measured voltage/current to strip:
>>>237 VAC / 20.0 A = 4.74 KW
>>>CFM = KW X 3514 X 1.08 / TR
>>>Hi speed: 19 F temp rise 74 to 93 = 947 CFM
>>>Mid speed: 21 F temp rise 72 to 93 = 857 CFM

>>I hate to break it to ya Jeanuis but your calculations are wrong.

>I agree. But your calculations are also wrong so there is no need for
>insults.
>I am not the HVAC expert. That is why I'm asking questions in this ng.

>>BTUH = I X E X 3.412
>>20a x 237v x 3.412 = 16172.88 BTUH
>>CFM = BTUH / temp rise X 1.08 @ sea level. The constant, 1.08 drops
>>slightly with altitude.

>Your formula doesn't agree with mine....

>>19 x 1.08 = 20.52
>>16172.88 / 20.52 = 788.15 CFM on high speed.

>I've gone back to check my original formula:
>At sea level (I can walk to the beach):
>TR = kW x 3412 x 1.08 / CFM
>(cross multiply to get CFM)
>CFM = kW x 3412 x 1.08 / TR
>CFM = 20 x 237 x 3412 x 1.08 / TR

This should be (20 x 237 / 1000) to change to kW
or use 3.412 (same end result)
Sorry for slip up......

>CFM = 4.74 x 3412 x 1.08 / TR
>CFM = 17466.7104 / TR
>Therefore:
>@ 21 F temp rise (mid-speed)
>CFM = 17466.7104 / 21 = 831.75
>@ 19 F temp rise (hi-speed)
>CFM = 17466.7104 / 19 = 919.26
>I've gone back to look at calculations I did back in Nov and these
>agree.
>Any comments?

>>16172.88 BTUH is electric heat not mechanical refrigeration BTUH.

>Thanks. That appears to be where I got the 3514 from. I don't know how
>I slipped it into the formula for original CFM this time. I've been
>taking a crash course in understanding HVAC so give me a break.

>>>Heat pump (about 40 F outdoor temp) w/o heat strip:
>>>BTU = CFM x TR / 1.08
>>>Using 856 CFM I came to 20,631 BTU for temp rise 72 to 98

>Is this correct?

Posted by Jean on February 20, 2009, 8:55 pm

On Fri, 20 Feb 2009 18:52:09 -0500, The King

>>On Fri, 20 Feb 2009 15:55:01 -0500, The King

>>>>The unit ran fairly quiet until recently. I'll take a video tomorrow
>>>>and upload to youtube.
>>>>Here's what I've checked out:
>>>>Airflow check using 5 KW aux heater strip w/o heat pump:
>>>>Air handler tested w/ ACTUAL measured voltage/current to strip:
>>>>237 VAC / 20.0 A = 4.74 KW
>>>>CFM = KW X 3514 X 1.08 / TR
>>>>Hi speed: 19 F temp rise 74 to 93 = 947 CFM
>>>>Mid speed: 21 F temp rise 72 to 93 = 857 CFM
>>>I hate to break it to ya Jeanuis but your calculations are wrong.

>>I agree. But your calculations are also wrong so there is no need for
>>insults.
>>I am not the HVAC expert. That is why I'm asking questions in this ng.

>Sorry Jeanius I was just trying to help you out and show you how to
>find the CFM and BTHU output based on the information you provided.
>You obviously don't want to learn anything. I don't know why I
>bothered. Go along in ignorant bliss, it's no skin off my back.

(snip)

Here's where I got my formula:

http://www.ncweb.com/~jsbuilders/aruf-aepf%20install.pdf

INSTALLATION & OPERATING
INSTRUCTIONS FOR
ARUF, ARPF, ADPF, AEPF
SERIES AIR HANDLER

page 5

                        HEAT KIT NOMINAL kW
CFM        3         5         6         8        10        15        20        21

600        18        28         35        41
800        13         21        26        31         42
1000        11        17        21        25        34        50
1200        9        14        18        21        28        42        56        62

        230/1/60 Supply Voltage - Temperature Rise Table °F

Note: For installations not indicated above the following
formula is to be used:
TR = (kW x 3412) x (Voltage Correction) x 1.08 / CFM

Formulas can be rearranged to find different unknowns. If this one
cannot, then it has been "fudged".

As you can see, the above chart shows that temp rise of 21 corresponds
to 800 cfm. A temp rise of 19 would put it at approx 900 CFM. This is
in agreement with my calculations. In point of fact, I could have used
the chart alone to check airflow and not bothered with formula.

I can only work with what I've been given. If you can give me a URL to
prove this data sheet wrong, I will gladly contact Goodman.

BTW, the HVAC tech has looked at the air handler and says it is OK.
Clean with good airflow and suitable intake location.

The 2 ton unit could have been smaller. The aux heat strip was only
activated for 3 or 4 days this heating season. I think I will add an 8
inch duct from the plenum (and corresponding air return) to heat a
small addition, 150 sq ft, that is currently heated with a 1.5 KW wall
unit. This will increase the airflow which is OK.

I was told by HVAC people that 400 CFM per ton is required but here is
a site that calls for up to 500:

http://www.gemplumbing.com/lmlb_heat_pump_improve_performance.html
"There should be about 400 to 500 cubic feet per minute (cfm) airflow
for each ton of the heat pump's air-conditioning capacity. Efficiency
and performance deteriorate if airflow is much less than 350 cfm per
ton."

Here's another URL that is of interest to me. My HVAC guy thinks that
the unit may have been factory overcharged.

http://www.gemplumbing.com/lmlb_heat_pump_adjusting_charge.html
"For satisfactory performance and efficiency, a split-system heat pump
should be within a few ounces of the correct charge, specified by the
manufacturer."

Posted by The King on February 20, 2009, 9:35 pm

snip

>Here's where I got my formula:
>http://www.ncweb.com/~jsbuilders/aruf-aepf%20install.pdf
>INSTALLATION & OPERATING
>INSTRUCTIONS FOR
>ARUF, ARPF, ADPF, AEPF
>SERIES AIR HANDLER
>page 5
>                        HEAT KIT NOMINAL kW
>CFM        3         5         6         8        10        15        20        21
>600        18        28         35        41
>800        13         21        26        31         42
>1000        11        17        21        25        34        50
>1200        9        14        18        21        28        42        56        62
>        230/1/60 Supply Voltage - Temperature Rise Table °F
>Note: For installations not indicated above the following
>formula is to be used:
>TR = (kW x 3412) x (Voltage Correction) x 1.08 / CFM
>Formulas can be rearranged to find different unknowns. If this one
>cannot, then it has been "fudged".
>As you can see, the above chart shows that temp rise of 21 corresponds
>to 800 cfm. A temp rise of 19 would put it at approx 900 CFM. This is
>in agreement with my calculations. In point of fact, I could have used
>the chart alone to check airflow and not bothered with formula.

Ok at a 21 DT with your numbers of 20a and 237v

CFM = volts x amps x 3.412 / 1.08 x temperature rise. Do the math

Your answer should be 735 CFM. If not you get another F.

You are misinterpreting the information from Goodman.

I'm honing my people skills so I can teach this shit and get out of
the truck. How 'em I doin? :)

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