Superheat

[Priceless32]

Whats a good accurate general rule of thumb for superheat? txv and fixed bore? Just curious about different opinions and views?

[Flashg21230]

If you have an iPad or iPhone their is an app called Hvac buddy that I like,it has a build in chart it will tell you what you sh should be given the condition at your particular location after you fill in the info like wet bulb,dry bulb,sat temps and so on,I don't know if any one here uses this app,but I find it helpful.

[garyed]

A while back hvacrmedic came up with a formula that works pretty well for target SH. I put it on a web page here:
http://www.loadcalc.net/superheat.php

[Dennis.Moore]

Whats a good accurate general rule of thumb for superheat? txv and fixed bore? Just curious about different opinions and views?
Try to keep it above zero. Not sure how "compliant" a compliant scroll is.
Most compressors are designed to pump vapor.

[KevinAdv]

So saturday I had a 95 degree od db and a 56 degree indoor wet bulb (yes there is no such thing as humidity here)

Acoording to my Fieldpiece Srh2

and that calculator http://www.loadcalc.net/superheat.php

I Should be flooding the compressor

What does that mean?

[AStudent]

Dupont has a nice app out now...although out of 5 guys in my class that downloaded the app all on android phones two worked properly....the other guys did not have the toolbar at the bottom of the screen.


http://www2.dupont.com/Refrigerants/en_US/uses_apps/PT_Calculator_app.html

[Flashg21230]

Have not seen that one on android,but I carry my iPad on service calls,the app I have will even let me email my results to my company or to the customer if they like.

[Flashg21230]

If you send me your email address I can send you a link to the app I have so you can check it out to see if you like it? I guess that's allowed on this site.when I first got on this forum I posted on the wrong place by mistake,as I wasn't familiar with how to post things.they were not happy about it.

[garyed]

So saturday I had a 95 degree od db and a 56 degree indoor wet bulb (yes there is no such thing as humidity here)

Acoording to my Fieldpiece Srh2

and that calculator http://www.loadcalc.net/superheat.php

I Should be flooding the compressor

What does that mean?

It means you need to be very careful charging under those conditions because your SH is going to be real low. I would probably look for 4* or 5* SH & leave it but some of the guys who work in your area might have a better solution. If you look at any manufacturers SH chart I'm pretty sure you will not find a reading at those temps. Here's two SH charts from two different manufacturers & you can see those conditions are blanked out on both.

[rednecktech]

If you send me your email address I can send you a link to the app I have so you can check it out to see if you like it? I guess that's allowed on this site.when I first got on this forum I posted on the wrong place by mistake,as I wasn't familiar with how to post things.they were not happy about it.


Me Too !! please .

[KevinAdv]

It means you need to be very careful charging under those conditions because your SH is going to be real low. I would probably look for 4* or 5* SH & leave it but some of the guys who work in your area might have a better solution. If you look at any manufacturers SH chart I'm pretty sure you will not find a reading at those temps. Here's two SH charts from two different manufacturers & you can see those conditions are blanked out on both.

I set it around 9-10 degrees I didn't really feel comfortable going lower because in the summer its between 105 and 110 normally and we still don't have humidity

[jpsmith1cm]

So saturday I had a 95 degree od db and a 56 degree indoor wet bulb (yes there is no such thing as humidity here)

Acoording to my Fieldpiece Srh2

and that calculator http://www.loadcalc.net/superheat.php

I Should be flooding the compressor

What does that mean?

In that case, you need to either wait until system conditions change or weigh in the factory charge plus lineset adjustments.

[hvac wiz 79]

A while back hvacrmedic came up with a formula that works pretty well for target SH. I put it on a web page here:
http://www.loadcalc.net/superheat.php

is this the: SH=(3xIWB-OD-80)/2 equation?

[Willserve]

It means you need to be very careful charging under those conditions because your SH is going to be real low. I would probably look for 4* or 5* SH & leave it but some of the guys who work in your area might have a better solution. If you look at any manufacturers SH chart I'm pretty sure you will not find a reading at those temps. Here's two SH charts from two different manufacturers & you can see those conditions are blanked out on both.

I agree don't let it get below 5* sh. What was the indoor temp? I'm in Florida the total opposite of what you have. I usually check line temp also to see how close I am to freezing. Is your air flow adjusted correctly? We slow our fans down to remove more humidity because of latent heat where as you have more sensible which may need more cfms 450 instead of 400.

[KevinAdv]

I agree don't let it get below 5* sh. What was the indoor temp? I'm in Florida the total opposite of what you have. I usually check line temp also to see how close I am to freezing. Is your air flow adjusted correctly? We slow our fans down to remove more humidity because of latent heat where as you have more sensible which may need more cfms 450 instead of 400.

Indoor temp was 78

If the duct system allows we could always use additional airflow this one didn't allow it

[garyed]

is this the: SH=(3xIWB-OD-80)/2 equation?
That's it,
The actual programming formula I use looks like this:
$_SH="superheat";
$wetbulb="indoor_wetbulb";
$ambient="outdoor_ambient";
$_SH=(($wetbulb * 3) - ($ambient + 80))/2 ;

I decided to cut it off when the SH gets below 4* & give the warning instead of computing it any lower.
At the OP's conditions the formula would give you a negative SH so the formula wouldn't be practical.

[Tech-M.J]

Normal superheat with txv in heating mode is 6 to 8 degrees

[Kevin Weaver]

on a no cool or a new install where a/c has been off awhile, rule of thumb for fixed metering device, 20 degrees.:eek:

[rdholder]

Superheat of a fixed orifice AC system is between 8 to 30 degrees depending on the IDWB (indoor wet bulb) and the Outdoor dry bulb. I have tested the SH= ((IDWB*3)-ODA)-80/2 formula and it is about +- 3 degrees of all the SH charts that I have. Do not use a rule of thumb to charge an AC system that why we have to change compressor. Charge the way the manufacture says to, that is most of the time superheat for fixed orifice and subcooling for a TXV.

[catmanacman]

I have a Trane ,Carrier,and Goodman superheat chart that i carry in my cooper thermometer there seems to be some difference in opinion as to what the superheat should be between the different manufactures ,i do not like to go less than 7 degrees superheat

[19degree]

IMOP I'm looking for a 9-12 degree superheat on piston systems for txv systems I check subcool because the txv should keep a constant superheat and I look for a 10-16 degree subcool.

[rdholder]

So saturday I had a 95 degree od db and a 56 degree indoor wet bulb (yes there is no such thing as humidity here)

Acoording to my Fieldpiece Srh2

and that calculator http://www.loadcalc.net/superheat.php

I Should be flooding the compressor

What does that mean?

Not all fixed orifice systems are designed to work in a dry climate; and therefore, when a superheat chart is at 6 degrees or below, the technician should never charge a fixed orifice below 6 degrees I like to never go below 8 degrees. This means you will have to under charging the system to maintain a working superheat. The weighing of a charge to manufactures spec’s will not work because they think that every place has the same humidity. From working in the desert, I have installed many TXV’s that will maintain superheat. Move the hole chart over so there is superheat. The suction line maximum temperature is 74 degrees or the compressor will overheat. Rheem total superheat below is not total superheat but it will work as long as the evaporator coil is within 2 degrees of design temperature.


..............................Vapor pressure at service valve
.................52.54.56..58.60.62..64.66..68.70. 72.74.76.78.80.82.84
Outdoor T°..............................Vapor line T° at compressor
F° 100+..................................43 45 46 47 49 50 51 53 54 55
100......................................44 45 47 48 49 51 52 53 55 56 57
95....................................45 47 48 50 51 52 54 55 56 58 59 60
90................................49 51 52 54 55 56 58 59 60 62
85...........................52 53 55 56 58 59 61 62 63
80......................53 55 56 58 59 61 62 63 65
75.................55 56 58 59 61 62 64 65 66
70............55 57 58 60 61 63 64 66 67
65.......57 58 60 61 63 64 66 67 69

[KevinAdv]

I have got the hang of it now I don't go any lower than 9 degrees On SH it may be a little undercharged but its better than a flooded compressor.


I have seen a lot of package units with pistons with superheats of only 2-3 degrees so thats how they come from the factory