Arkansas HVACR NewsMagazine June 2018

HVACR NewsMagazine June 2018 Tech News

kept at cellar temperature. Craft Beer enthusiasts will tell you that about 45°F (7.22°C) is a good compromise between flavor and temperature. On average, your evaporator temperature will have a 35°F (19.25°K) DTD (Design Temperature Difference) which means the coil temperature will be about 35°F (19.25°K)) colder than the return air DB temperature. This means if it’s 75°F (23.88°C) in the return the evaporator will be at about 40°F (4.44°C). We then need to add in superheat which will vary quite a bit on a fixed orifice system. On a TXV or EEV system it will be between 5°F and 15°F (2.75°K – 8.25°K) on a properly functioning system. This means that the suction line indoors could range from 45°F to 55°F (24.75°K – 30.25°K) by the time you account for the TXV superheat range, the uncertainty of the temperature measurement and the variability in DTD. If you are grabbing the suction line outside, you will also need to account for anywhere from a 1°F to a 8°F (.55°K – 4.4°K) rise in temperature on the suction line by the time it get’s from the coil to the outdoor unit where “Beer Can Cold” is taken. Now the range is all the way from an acceptable beer temp of 46°F All of this, just at 75°F (23.88°C) return temperature WITH a TXV. (7.77°C) all the way up to a putrid 63°F (17.22°C) that even the British would find unacceptably warm. I don’t know about you, but my hand is only calibrated to within +/- 4°F(2.2°K), when you add that to the mix I find that using my hand to feel the suction line gives me only the roughest estimation of what is going on and if 50°F (10°C) is the average… that is too warm for my taste in beer anyway.

Beer can cold, like most “rules of thumb” is far too inaccurate to be useful (at the risk of overstating the obvious). What I do recommend, is becoming fully familiar with…. • The Design CFM of the System and the sensible / latent requirements of your area • The efficiency of the equipment you are working on (to help anticipate condensing temperature) • Type of metering device (To understand target superheat) • Evaporator Coil Design Temperature Difference (DTD) • Condensing Temperature Over Ambient (CTOA)

• Superheat • Subcooling • Delta T • Static pressure

Add a good understanding of all of these readings and when and where to take them in the mix and THEN and ONLY THEN have you earned the right to make jokes about beer can cold. If you have not yet understood the concepts I would advise starting by reading THIS and then listening to THIS

This article was provided by Bryan Orr with HVAC School for Techs. HVAC School for Techs has a plethora of material including articles, newsletters, podcasts, and videos. Link to their site @ https://hvacrschool.com/