Condensing Temperature, Condenser Split and Subcool

HVAC School - For Techs, By Techs

Bryan Orr

Training, Careers, Airconditioning, Self-improvement, Hvac, Business, Education, Refrigeration, Heating, Ac, Apprenticeship

4.8 • 985 Ratings

🗓️ 22 February 2017

⏱️ 32 minutes

🔗️ Recording | iTunes | RSS

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Summary

In this podcast, Bryan talks about condensing temperature, condenser split, and subcooling. All three of the values are proportional. If one changes, all three of them will change. Saturation is also a critical concept that relates to all three of those, so we also cover those relationships.

As you remember, a condenser rejects heat and turns vapor refrigerant back into a liquid.

Condensing temperature is the saturation temperature at which the refrigerant changes from vapor to liquid; it can change depending on ambient temperature. While in the condenser, the refrigerant will be at saturation and be a liquid-vapor mix throughout most of the coil.

Subcooling indicates how low a liquid is below liquid-vapor saturation. For example, if you had a condensing temperature of 110°F and took a liquid line measurement of 98°F, you would have 12°F of subcooling (110 - 98 = 12). Although some high-SEER HVAC systems may get their liquid line temperatures pretty close to the ambient temperature, you cannot have a liquid line temperature below the ambient temperature. Otherwise, you probably have a restriction in the line. Many technicians set a charge based on subcooling.

Condenser split is a bit trickier to define. You DON'T compare the temperatures of air going into the condenser and air going out. Instead, it is the difference between the condensing temperature and the outdoor temperature. The outdoor temperature MUST be lower than the condensing temperature. Otherwise, heat rejection cannot take place. In general, most manufacturers tend to engineer their HVAC systems to maintain a 15-30°F condensing split.

Heat mode has its own set of challenges. For example, subcooling can be difficult to predict in heat mode. However, between 20-30°F of subcooling in heat mode is normal.

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Transcript

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0:00.0	The following podcast is made possible by generous support from Testo and Carrier.
0:09.0	Now just yesterday we actually installed four carrier systems at a single house, is actually a friend of mine's house and I was able to use a bunch of
0:15.4	testo products in order to confirm the system operation and a tool that I
0:20.1	really like that I just got from testo is called the Testo 605 I and it's part of their smart
0:25.4	probes kit and what it is is an induct cychrometer hygrometer or whatever you want to call
0:30.7	it but it's a they call it a hygrometer, and it measures both temperature and
0:34.8	humidity. And when we say humidity, it's not just relative humidity, although it can measure
0:39.4	relative humidity, but it can also measure by getting your relative humidity as well as your dry bulb
0:45.0	you can also calculate wet bulb and you can calculate due point.
0:48.0	And what a lot of people don't know is that with a very simple tool like this you can do a little math and actually calculate the entire
0:55.0	capacity of the system.
0:56.8	You just have to do it in two steps.
0:58.0	So in the systems that I was working on, these are heat pump systems.
1:01.8	So you just have to run the electric heat because as you
1:03.9	know electric heat strips put out a set amount of output so then you calculate
1:08.6	your airflow using that and that's the that's the hard way of doing it in the
1:11.6	case of these carrier infinity systems that I was
1:13.6	installing they actually give you the exact CFM that they're outputing especially
1:17.5	in test mode you can set them up and see all of your different specs as you're
1:20.8	testing it but if you want to do it the hard way,
1:22.9	or if you have a system that doesn't give you that type of data
1:25.3	like the carrier infinity system gives you,
	...

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