Total Heat of Rejection - Short #152
HVAC School - For Techs, By Techs
Bryan Orr
4.9 • 1K Ratings
🗓️ 30 August 2022
⏱️ 10 minutes
🧾️ Download transcript
Summary
In this short podcast, Bryan talks about THOR, total heat of rejection. He explains what it is and why we should care about it when working on HVAC/R systems. THOR is another aspect of pressure-enthalpy calculations, along with net refrigeration effect (NRE) and total heat of compression.
When we talk about system capacity, we're often referring to heat absorbed in the evaporator coil (NRE). Heating is on the opposite side of the coin; when we bring heat into a home, we care more about how much heat is rejected than absorbed. That's where THOR comes in.
More heat is rejected at the condenser than absorbed in the evaporator. The total heat content increases due to additional heat being absorbed in the suction line. Compressors also have motors that aren't 100% efficient, so a bit of inefficiency also adds a small amount of heat to the refrigerant (in a system operating normally). All of that heat adds up to the total heat of rejection (THOR).
Even though a higher total heat of rejection is desirable when we want heat pumps to bring heat into the home, we don't want our compression ratios and discharge temperatures to get too high. We have to avoid oil breakdown and other negative effects. So, modern heat pumps use variable frequency drive technologies or liquid or vapor injection to get a lot of capacity out of the compressor without overheating it.
The effective THOR only happens in the condenser. Some heat rejection may occur in the discharge line, but none of that is of use to us when we need to bring heat indoors.
Check out Eugene Silberstein's book, Pressure Enthalpy Without Tears, at https://escogroup.org/shop/itemdetail.aspx?ID=1445.
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Transcript
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| 0:00.0 | Hey, hey, what do you say? |
| 0:05.0 | H.C School Podcast, Brian Orr here. |
| 0:09.0 | We're going to do a short episode here, |
| 0:11.0 | because we've gotten behind on short episodes. |
| 0:12.0 | And this is another one in our series where we're talking about some terms |
| 0:15.2 | The technicians don't use a lot, but especially if you're going to be working with pressure enthalpy charts |
| 0:19.5 | Getting a little bit more into the engineering side just understanding it more about the |
| 0:23.8 | systems that we work on every day these are some terms you should know and today we're |
| 0:27.5 | talking about Thor and no we're not discussing the Norse god of thunder although |
| 0:32.0 | that is always a common discussion point in my home at least. |
| 0:35.2 | We're talking about total heat of rejection. So before we do that, though, we want to thank our great |
| 0:40.1 | brand sponsors. Refrigeration Technologies can be found at refrigidjectec.com. |
| 0:47.0 | They make all kinds of great products and chemicals for the HVAC trade. |
| 0:50.0 | Specifically one that I love is called Wet rag. Wet rag kind of works like a |
| 0:54.3 | wet rag but it's easier to use. You can pack it around valves. You can use it to |
| 0:58.6 | protect the liquid line dryers and compressors or accumulators or whatever you happen to be braising in. And then when you're done you can just return it to the canister if you need |
| 1:07.3 | to rejuvenate it just use a couple little drops of water in it and it will rejuvenate |
| 1:11.8 | and be ready to use next time. |
| 1:13.8 | That is wet rag from refrigeration technologies. |
| 1:16.7 | Find out more at refrig tech.com. |
| 1:20.7 | carrier and carrier.com. |
| 1:23.0 | Navac at Navac Global.com |
... |
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