1 / 14

Metering Devices

Metering Devices. North Seattle Community College HVAC Program Instructor – Mark T. Weber, M.Ed.

gautam
Download Presentation

Metering Devices

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Metering Devices North Seattle Community College HVAC Program Instructor – Mark T. Weber, M.Ed.

  2. RULE 1     Life  is not fair - get used to it.RULE 2     The  world won't care about your self-esteem. The world will expect you to accomplish something BEFORE you  feel  good about yourself.RULE 3     You  will NOT make 40 thousand dollars a year right out of high school. You won't be a vice president with car phone, until you earn  both.RULE 4     If  you think your teacher is tough, wait till you get a boss. He doesn't have tenure.RULE 5     Flipping burgers is not beneath your dignity. Your grandparents had a different word for burger flipping; they called it Opportunity.RULE 6     If  you mess up, it's not your parents' fault, so don‘t whine about your mistakes, learn from them.RULE 7     Before you were born, your parents weren't as boring as they are now. They got that way from paying  your bills, cleaning your clothes and  listening to you talk about how cool  you are. So before you save the rain forest from the parasites of your parent's generation, try delousing the closet in your own room.RULE 8     Your  school may have done away with winners and losers, but life has not. In some schools they have  abolished failing grades and they'll  give you as many times as  you want to  get the right answer. This doesn't bear the slightest resemblance to ANYTHING in real life.     RULE 9     Life  is not divided into semesters. You don't get summers off and very few employers are interested in helping you find yourself. Do that on your own  time.RULE 10     Television is NOT real life. In real life people actually have to leave the coffee shop and go to  jobs.RULE 11     Be  nice to nerds. Chances are you'll end up working for one.

  3. Key Points on Expansion Valves: • Thermal Expansion Valve Systems are charged primarily by sub-cooling • Since the TXV is designed to regulate a constant superheat, the actual superheat just needs to be “checked” to make sure the valve is performing correctly • Design Superheat: 10-15 degrees • Field Superheat: 8-28 degrees

  4. Compressor Sensing bulb & capillary tube Diaphragm Evaporator Condenser Equalizer tube Liquid refrigerant from condenser Liquid refrigerant to evaporator Needle valve TXV Valve body Superheat spring

  5. Compressor Sensing bulb & capillary tube As the vapor refrigerant enters the condenser, it starts to give off heat. It will remain at its saturation temp until it has completely turned into a liquid. Diaphragm Evaporator Condenser Equalizer tube Liquid refrigerant from condenser Liquid refrigerant to evaporator Needle valve TXV Valve body Superheat spring

  6. Compressor Sensing bulb & capillary tube We want about 10 – 15 % liquid refrigerant at the bottom of the condenser. Because it is still warmer than the air passing by it, it will continue to give off heat. This is when its sensible temp falls below its saturation temp. This is subcooling. Diaphragm Evaporator Condenser Subcooled refrigerant Equalizer tube Liquid refrigerant from condenser Liquid refrigerant to evaporator Needle valve TXV Valve body Superheat spring

  7. Compressor Sensing bulb & capillary tube Diaphragm Evaporator On the other side, the liquid refrigerant enters the bottom of the evaporator. Because it is cooler than the air passing over it, it absorbs heat. We want about 10 – 15% liquid at the bottom and for it to turn completely into vapor by the time reaches the top 25%. Because it is still cooler than the air it will continue to absorb heat and its sensible temp will rise above its saturation temp. This is superheat. Condenser Equalizer tube Liquid refrigerant from condenser Liquid refrigerant to evaporator Needle valve TXV Valve body Superheat spring

  8. Compressor Sensing bulb & capillary tube Diaphragm Evaporator Condenser Equalizer tube Let’s see this in operation. With the compressor off, we have approx. equal pressure on both sides and the sensing bulb is about 1/3 liquid refrigerant and 2/3 vapor. Needle valve Now, let’s add some gauges and thermometers.

  9. Compressor Sensing bulb & capillary tube Diaphragm Evaporator Condenser 95 Equalizer tube Needle valve There is a call for cooling and the compressor and condenser fan start. The condenser fan is pulling 95 degree air over the condenser coils. Because the needle valve is closed, the compressor quickly builds up pressure on the high side of the system.

  10. 364 Compressor Sensing bulb & capillary tube Diaphragm Evaporator Condenser 95 Equalizer tube Needle valve Lets make this a SEER 13 system. With a SEER 13 system, we want the condenser coil to have a saturation temperature 15 degrees warmer than the air passing over the coil. With R410a and a saturation temp of 110 (95+15), the pressure needed is 364 PSIG. Because the needle valve is closed, the compressor quickly builds up pressure on the high side of the system.

  11. 364 Compressor Sensing bulb & capillary tube Diaphragm Evaporator Condenser 126 95 Equalizer tube The indoor blower has also started and the air passing over the evaporator coil is 75 degrees and 60% R.H.. With a 60% R.H., we want a temperature drop of 12 – 17 degrees. In addition, we want our superheat in the range of 10 – 15 degrees. 17 + 15 = a temperature difference of 32 degrees. 75 – 32 = 43 degrees for our saturation temperature. That equals a pressure of 126 PSIG Needle valve Because the needle valve is closed, the compressor suction quickly lowers the pressure on the low side of the system.

  12. 364 Compressor Sensing bulb & capillary tube Diaphragm Evaporator Condenser 126 95 Equalizer tube To keep the two sides in balance, the needle valve has to open and close to allow the correct amount of refrigerant pass through Needle valve If the needle valve were to remained closed, the pressure on the high side would continue to rise and the pressure on the low side continue to drop.

  13. 364 Compressor Sensing bulb & capillary tube Diaphragm Evaporator Condenser 126 PSIG 126 95 Equalizer tube Needle valve

More Related