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Old 07-30-2009, 02:26 PM   #1
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HVAC flow rates and pressures. Cunning install ideas?


Just to introduce myself, I am an aerospace engineer and installing a somewhat unknown Tempstar heatpump system in an older 1000sf home so I can sell it. The house is one story, no basement, junk insulation, junk windows, in KS, leaks like crazy. I have some general HVAC knowledge and much more in the electrical areas, good friend is a commercial HVAC designer but little help on rezzy stuff. I am looking for a fast, cheap way to climate control this old house. Right now it has a window unit and floor furnace.


Units are Tempstar, condenser model is CH5030, min amps is 17.9A and max fuse is 30A, indicates 8500 watts cooling. furnace only tells me 75K btu input. Not much to go on. Per some others' remarks, these units are likely 2.5Ton or 1000cfm. Furnace is updraft with a 14x19 opening.


PLAN:

Punch hole straight down in subfloor and use stud network to create return passages and instal (2)13x19 return ducts in the lower part of the walls. Due to tight floor space, I do not want them in the floor but I realize that is easiest. I plan to get a basic plentum made for the output that is 14x19xroughtly 48 tall to extend into the attic. I will then punch multiple holes for collars to install insulated ducting for the positive venting of the home. sizing is all open right now

Questions:

Idea on how big these units really are?

What should my target unit size be given the condition of this home and its climate?

Can someone help with flow numbers for vents, insulated duct sizes, returns, etc? This seems to be my biggest problem right now. I have no idea what pressures I will or should be operating at.


Is it best to match the flows of the returns and pos vents? I am worried about the house leaking worse if drawing in ambient air or even forcing it out.

In using the floor joists for return porting, how is that commonly sealed up? Does one build sheet metal venting into it or just apply a sealer and skin over it with sheet metal?

ALso, because my units are actually heat pump designs, would anyone advise using it as such? I have heard not to even mess with it and I planned to just use the gas furnace for heating. My understanding of them is that the flow of refrigerant is reversed thus using the A coil as a condenser which just seems poorly efficient to me....


Any help would be greatly appreciated guys. I have to move on this project in about 3 weeks.

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Old 07-30-2009, 05:07 PM   #2
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HVAC flow rates and pressures. Cunning install ideas?


Hey...it ain't Rocket Science....

































































It's Thermodynamic Science.


I cringe when I hear cheap and quick. Reminds of that guy who didn't use the metric conversion factor that caused us to lose a MARS probe.

Go cheap on an install you get the same result.

Somebody will be along to advise you soon. I just don't like cheap and quick. Dumbs me down real quick. I like people who I give advice to to stay alive.

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Old 07-30-2009, 05:29 PM   #3
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HVAC flow rates and pressures. Cunning install ideas?


Quote:
Originally Posted by viper View Post
indicates 8500 watts cooling. these units are likely 2.5Ton or 1000cfm.
2.5T = 30,000 BTU/hr = 8800w at a COP of 1.0. . .?
18A @ 240v = COP of 2. . .? Talk about the hidden cost of ownership. . .!

For heating it's 6 BTU/sq. ft/HDD with a wide tolerance on this number. 1.7 is excellent, a very tight house.
You might want to look at HVAC stuff published by ASHRAE, ACCA or Audel's.
This book
http://ppi2pass.com/ppi/PPIShop_ct_M...FdBB5godCyic-g
is commonly available at libraries.

The Mars probe being lost reminded me of the work of engineers who are "political appointees". I met at least one at Litton-Amecom, back when it was called that.

Last edited by Yoyizit; 07-30-2009 at 05:42 PM.
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Old 07-30-2009, 06:03 PM   #4
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HVAC flow rates and pressures. Cunning install ideas?


Quote:
Originally Posted by Yoyizit View Post
2.5T = 30,000 BTU/hr = 8800w at a COP of 1.0. . .?
18A @ 240v = COP of 2. . .? Talk about the hidden cost of ownership. . .!

For heating it's 6 BTU/sq. ft/HDD with a wide tolerance on this number. 1.7 is excellent, a very tight house.
You might want to look at HVAC stuff published by ASHRAE, ACCA or Audel's.
This book
http://ppi2pass.com/ppi/PPIShop_ct_M...FdBB5godCyic-g
is commonly available at libraries.

The Mars probe being lost reminded me of the work of engineers who are "political appointees". I met at least one at Litton-Amecom, back when it was called that.

OOOOOHHH GoD>>>> I guess you showed him HVAC IS Rocket Science!


My sides hurt you SOB
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Old 07-30-2009, 07:36 PM   #5
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HVAC flow rates and pressures. Cunning install ideas?


Thanks for the replies.

Good God, I did not look at the EER but....

17.9A * 240V = 4296watts

rated output is 8500 watts or 29000 BTU which assumes about 15K of that through latent heat of vaporization.

EER is 6.75!!!!!!

Now this is assuming the badging on the condenser is accurate and rates at continuous. I realize that badge has to be calculated as well for the inrush of the compressor so I guess I will not know for sure until it runs..... The system is from 1990. Does that even seem feasible?

I realize the EER needs to be calculated under certain conditions for accuracy like 72*F, 40% humidity, 90*F ambient, etc. When I have done calcs on some window units, it was usually within 1 EER of rated once I got the amp pull from the unit. Of course on this one, I do not know if this is assuming the air handler or not. That has to be figured in too!!


What is HDD (heating degree days) in your below calc.? Where are you getting this 6 BTUs from? Does this assume 8ft ceiling, vaulted, etc? Why are calcs done from sf instead of ft3 which would be a bit more accurate?


Thanks for the heads up on the reading.

By the way, what is the standard operating pressure range for Residential systems?

Last edited by viper; 07-30-2009 at 07:41 PM.
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Old 07-30-2009, 07:46 PM   #6
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HVAC flow rates and pressures. Cunning install ideas?


Hey viper I don't mean to be rude but were you the guy who crashed our MARS lander?
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Old 07-30-2009, 07:48 PM   #7
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HVAC flow rates and pressures. Cunning install ideas?


Quote:
Originally Posted by viper View Post
Where are you getting this 6 BTUs from? Does this assume 8ft ceiling, vaulted, etc? Why are calcs done from sf instead of ft3 which would be a bit more accurate?
It's an average I've heard about from Smart Home or some such magazine, and is somewhat confirmed from my histogram of the few samples I've gotten.
Here's somebody who used this method.
http://www.focusonenergy.com/files/D...udy_report.pdf
The 1.7 and the 4.4 are from this study so they should be weighted much more heavily than the other datapoints.

From the Law of Large Numbers, the more samples I get the less important is the accuracy of each sample.

1.7 least heat loss
3.8
4.0
4.4
5.7
8.0
8.8
11 most heat loss

Histogram
0 to <3|x
3 to <6|xxxx
6 to <9|xx
9to<12|x

HVAC is kind of rocket science. It's worse than elec. eng. because it's three dimensional and non-linear. That's why ASHRAE makes so many tests and measurements.

Last edited by Yoyizit; 07-30-2009 at 07:52 PM.
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Old 07-30-2009, 07:50 PM   #8
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HVAC flow rates and pressures. Cunning install ideas?


By the way, what is the standard operating pressure range for Residential systems? Last edited by viper; Today at 08:41 PM.


Depends on the indoor and out door conditions, An't no ball park or STANDARD condition cause they change too variably.
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Old 07-30-2009, 08:00 PM   #9
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HVAC flow rates and pressures. Cunning install ideas?


Where in KS?
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Old 07-30-2009, 08:03 PM   #10
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HVAC flow rates and pressures. Cunning install ideas?


Quote:
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Hey viper I don't mean to be rude but were you the guy who crashed our MARS lander?


OH man, you don't want to go there, LOL. Twin brother is an engineer for NASA. If some only knew the math it takes just to get to space, let alone land 1B miles away.

I actually design off road racing parts, aero structure assembles, and a few PCB design circuits and PLC controls. I am more mechanic, my brother is more fluid dynamic and thermodynamic oriented.

House I am doing is more of a training project because I have a 12000sf building to climate control next and I want to step up the technology a bit. We started playing with friggin IR sensing and wireless smart circuits a while back and itching to "take it all the way" Gotta pop my cherry first I guess and get some basic numbers out of the way.
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Old 07-30-2009, 08:08 PM   #11
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HVAC flow rates and pressures. Cunning install ideas?


Quote:
Originally Posted by Yoyizit View Post
It's an average I've heard about from Smart Home or some such magazine, and is somewhat confirmed from my histogram of the few samples I've gotten.
Here's somebody who used this method.
http://www.focusonenergy.com/files/D...udy_report.pdf
The 1.7 and the 4.4 are from this study so they should be weighted much more heavily than the other datapoints.

From the Law of Large Numbers, the more samples I get the less important is the accuracy of each sample.

1.7 least heat loss
3.8
4.0
4.4
5.7
8.0
8.8
11 most heat loss

Histogram
0 to <3|x
3 to <6|xxxx
6 to <9|xx
9to<12|x

HVAC is kind of rocket science. It's worse than elec. eng. because it's three dimensional and non-linear. That's why ASHRAE makes so many tests and measurements.

Thanks for the posts and links. I will absorb the knowledge you sent.

Per some research, it seems .1inH2O might be a target number for pressures. I would assume additional pressures would get you nothing but noise and reduced efficiency due to frictional losses. Thus, bigger pipe!
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Old 07-30-2009, 08:09 PM   #12
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HVAC flow rates and pressures. Cunning install ideas?


Give my regards to your brother and tell him I am constantly on my state reps ass to increase NASA's budget.


I hope I live to see NASA build a fighter space ship. I could die a happy man, I am such a space geek!
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Old 07-30-2009, 08:26 PM   #13
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HVAC flow rates and pressures. Cunning install ideas?


Oh Gawd, not another trekkie! My ex boss Jean, we called him Jean Luc "make it so".
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Old 07-30-2009, 08:31 PM   #14
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Quote:
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Oh Gawd, not another trekkie! My ex boss Jean, we called him Jean Luc "make it so".
Shddup. Its your fault Shatner is from Canada!

But truly I love Sci Fi.
graphy - William Shatner Spotlight

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Old 07-31-2009, 02:27 PM   #15
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HVAC flow rates and pressures. Cunning install ideas?


Basic numbers that I have right now are:
6" - 80-100cfm
7" - 115-150cfm
8" - 175-225cfm

These all assume flex duct, .1in H2O ballpark, and no more than a 50ft run. Does this seem in line? My biggest problem is that damn flex is hard to calculate due to the increased turbulence in the line. The stuff I want has the foil inner wall and not just the bare insulation.


Also, to maintain max efficiency, the calculated flow of the RA ducting should be about 20% larger than the output to minimize depression and noise at the RA ducts.

Am I in the ballpark with this stuff?

Also, does anyone have some files on Manual J calcs? I would like to learn a bit more on heat loss/gain factors commonly used. My goal is to be able to calculate ROI of different approaches to climate control whether it be added insulation, white exterior paints, etc.

As noted, we are going to be doing several things in our other new building including closed loop floor heat/cool. I will run a a supplemental HVAC system on that but would like the floor system to handle plenty. I want to design a wood or oil fed boiler for the water heating in the floor. Heating 12K sf can get expensive!

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