-
psycrometer
Is a sling psycrometer required to acuaratly calculate superheat and subcooling as well as a temperature probe. All we have at work is a laser\infered thermometer . Thanks guys and gals
-
I'll give the short answer and let the more experienced techs give explanations...
Yes... Get rid of the infrared. Get one.. And some temp probes.
Sent from my GSIII on Tapatalk
-
 Originally Posted by andersonbe06
Is a sling psycrometer required to acuaratly calculate superheat and subcooling as well as a temperature probe. All we have at work is a laser\infered thermometer . Thanks guys and gals
An indoor wet bulb temperature is needed to determine the required superheat on a unit using a fixed metering device. As wet bulb temperature increases, more superheat is required.
On a system using a Thermal Expansion Valve (TXV), the required superheat is maintained by the TXV. That is why on these systems you need to charge by subcooling.
I too have never been a fan of infrared thermometers for measuring liquid and suction line temperatures.
Instead of learning the tricks of the trade, learn the trade.
-
No. It it not required. In fact i see no use for a sling psycrometer when checking superheat or subcooling. A temperature probe, a gauge and a pt chart is what you need
-
 Originally Posted by andersonbe06
Is a sling psycrometer required to acuaratly calculate (target ) superheat and subcooling as well as a temperature probe. All we have at work is a laser\infered thermometer . Thanks guys and gals
the answer is yes or a wet bulb thermometer and a convoluted mathematical formula.
 It`s better to be silent and thought the fool; than speak and remove all doubt. 
-
As others have stated, on fixed metered systems you need to know the wet bulb temperature of the air entering the indoor coil to know the required superheat.
Rather than a sling psychrometer for measuring the indoor wet bulb temperature, I highly recommend a psychrometer that has a probe that can be inserted through a test hole to measure the wet bulb and dry bulb temperatures where they are entering the indoor coil.
My current favorite is the Fieldpiece SDP2,
Most people seem to be unaware that the old standard sling psychrometers are inherently less accurate, rated for +/-5% RH, than most decent digital psychrometers, typically rated at +/-2 or 2.5%RH.
Retire the IR gun to looking for hot electrical connections/breakers, and big temperature differences in wall sections.
Many people have come up with, and/or been taught methods that they "never had a problem" with, but in every study that has been done, anywhere from 54% to over 70% of the systems checked during the study were significantly over or under charged by >10%, so clearly there is a big frickin problem...
 Originally Posted by adam_s05
No. It it not required. In fact i see no use for a sling psycrometer when checking superheat or subcooling. A temperature probe, a gauge and a pt chart is what you need
On fixed metered systems, without the wet bulb temperature of the air entering the indoor coil, how do you know what your superheat is supposed to be?
-
I use this formula. (Thanks HVACMedic)
(3 x Entering Wet Bulb - 80 - Outdoor Temp) / 2 = Target Superheat.
-
 Originally Posted by andersonbe06
Is a sling psycrometer required to acuaratly calculate superheat and subcooling as well as a temperature probe. All we have at work is a laser\infered thermometer . Thanks guys and gals
All that is required to measure SH / SC is pressure gauges, temperature probes, and P/T chart.
WB may or may not be required to determine target SH / SC, depending on the unit's charging chart.
-
Anybody tried wrapping a little bit of a wet paper towel around a temperature probe? It was within 1 degree of actual WB.
-
 Originally Posted by bobster
All that is required to measure SH / SC is pressure gauges, temperature probes, and P/T chart.
WB may or may not be required to determine target SH / SC, depending on the unit's charging chart.
majority if not all SH charts have wet bulb that i remember looking at lately. And with the DB out and WB inside, superheat can be anywhere from 30 to 6 (or something like that)
-
-
 Originally Posted by penderway
FYI, Any chart that doesn't require a wet bulb input assumes 50% indoor relative humidity.
Yeap, they assume 50% RH, and that the space is at, or very near, the normal temperature it is kept.
Rheem/Ruud, and a few others have charts based on just the outdoor DB and suction pressure, or outdoor and indoor DB.
Those charts are merely a dumbed down compromise by manufacturers that understand the sad reality of how most "technicians" operate, and came up with a simple charging procedure that will usually not result in to many dead compressors if followed.
If the RH is significantly higher or lower than 50%, or the space is not at or near normal temperature, the chart cannot be used.
I pretty much ignore those kinds of charts on split systems, but will go by whatever off the wall weirdness for a charge checking procedure I find on a sticker on a package unit. 
My personal favorite screwy charging procedure is Lennox's subcooling method for fixed orifice systems.
I'm still:[IMG]http://1.bp.********.com/_wAxDMfEGhoY/TQrlbN4gYXI/AAAAAAAAAXg/kmwztAAni44/s400/Not+Sure+if+serious.jpg[/IMG]
-
 Originally Posted by mark beiser
Yeap, they assume 50% RH, and that the space is at, or very near, the normal temperature it is kept.
Rheem/Ruud, and a few others have charts based on just the outdoor DB and suction pressure, or outdoor and indoor DB.
Those charts are merely a dumbed down compromise by manufacturers that understand the sad reality of how most "technicians" operate, and came up with a simple charging procedure that will usually not result in to many dead compressors if followed.
If the RH is significantly higher or lower than 50%, or the space is not at or near normal temperature, the chart cannot be used.
I pretty much ignore those kinds of charts on split systems, but will go by whatever off the wall weirdness for a charge checking procedure I find on a sticker on a package unit.
My personal favorite screwy charging procedure is Lennox's subcooling method for fixed orifice systems.
I'm still:[IMG]http://1.bp.********.com/_wAxDMfEGhoY/TQrlbN4gYXI/AAAAAAAAAXg/kmwztAAni44/s400/Not+Sure+if+serious.jpg[/IMG]
The package unit comment took me back a few hours today when tge boss told me to figure how much freon is in the equipment at one of our accounts.... Would be nice if they were packs, but since tgey are all 5-30 ton splits with varying line sizes... I may be figuring for a while! Ill go gst rough lineset distances tomorrow and calculate what ammount is supposed to be there...
Sent from my SCH-I500 using Tapatalk 2
Posting Permissions
- You may not post new threads
- You may not post replies
- You may not post attachments
- You may not edit your posts
-
Forum Rules
|
Related Forums
The place where Electrical professionals meet.
|