Q&A on Superheat - Short #223

HVAC School - For Techs, By Techs

Bryan Orr

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

4.8 • 985 Ratings

🗓️ 24 December 2024

⏱️ 10 minutes

🔗️ Recording | iTunes | RSS

🧾️ Download transcript

Summary

In this short Q&A podcast episode, Bryan answers a listener-submitted question about superheat, including what it is and how we measure it.

Superheat is the number of degrees a refrigerant is above its saturation point. The saturation point is where you will have a liquid-vapor mix, so superheat only exists when a substance is a vapor. Saturated refrigerant should only exist in the evaporator and condenser, during which it is being boiled or condensed.

We usually measure superheat at the evaporator coil outlet and compressor inlet. The superheat at the evaporator outlet is usually around 5-14 degrees Fahrenheit, and it's often between 10 and 20 degrees at the compressor inlet (compressor superheat). However, many systems try to get lower superheat values, and some manufacturers may require higher superheat values at the compressor inlet to prevent liquid refrigerant from getting into the compressor. Accumulators can help keep liquid refrigerant out of the system as well. We may also measure superheat coming out of the compressor on the discharge line (discharge superheat); this superheat may exceed 100 degrees Fahrenheit. Discharge superheat can let you know if the compressor is overheating the oil and causing breakdown or carbonization.

We use superheat to set the charge for fixed-orifice metering devices (as opposed to subcooling for TXVs), as superheat is a measure of how well we're feeding our evaporator coil. When the system is off, the superheat will be 0. A system will equalize, and the refrigerant will be at saturation when that happens.

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Transcript

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0:00.0	Hello, hello. This is the HVAC school podcast, and we got a rather unique Q&A today on the topic of Superheat.
0:12.3	Before we get to that, we want to thank our great sponsors. Carrier and Carrier.com,
0:17.4	White Rogers and Copeland, and especially their connected controls.
0:23.2	HVCRSchool.com slash connect controls to find out more about Copeland and White Rogers.
0:28.9	Navak at navakglobal.com.
0:32.1	Refrigeration technologies at refrigetec.com and specifically the new Viper Wetrag Heat Shield.
0:39.0	The revolutionary flame-resistant welding pad designed to be used either wet or dry.
0:45.8	Find a Viper wet-rag heat shield at a distributor near you or go to TrueTechTools.com
0:50.8	and use offer code, get schooled for a great discount at checkout.
0:55.0	Fieldpiece, fieldpiece.com.
0:59.8	So here is the question.
1:02.2	Now you notice the question is in Spanish.
1:05.6	Now you notice the question is in Spanish.
1:08.5	So I'm going to answer it in English because that's the only language I speak, but it does remind me that we do actually have a lot of Spanish listeners.
1:15.4	So I'm going to see about doing a transcribed version of this for a future episode in Spanish, but for now, I can only answer the way I can answer.
1:22.8	And when people ask me about super heat, but gosh, there's always so much to talk about.
1:26.0	So we might as well just do a short episode on it. And we'll start with the basics. So first off, what is super heat?
1:31.8	The question of what it is versus how it's measured. So there's first the scientific answer,
1:36.8	which is just super heat, is any temperature that's picked up above the boiling point or above the
1:43.3	saturation temperature. So when you think about any particular refrigerant at a given pressure point or above the saturation temperature.
1:44.5	So when you think about any particular refrigerant at a given pressure, it has a given saturated
1:48.8	temperature. Saturated just means if it has refrigerant that is a mix of vapor and liquid
	...

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