An air conditioning system will not operate properly and will lose cooling capacity if the evaporator coil becomes blocked with frost or ice. Even though there is all that ice on the evaporator coil the cool air flow out of the system will be reduced as air flow across the coil becomes less and less as the ice area grows.

Why Frost or Ice Forms on an Evaporator Coil

Frost line on the cooling coil: When liquid refrigerant enters the evaporator coil temperatures may be as low as 10 degF at that point – that is at the top of the coil at the point of refrigerant entry. In normal operation of a refrigeration system, air movement across the evaporator coil provides enough warmth that frost or ice do not form on the coil.

In fact, as one sees in a refrigeration class, releasing liquid refrigerant into a coil over which air is not being blown will quickly result in frost formation on the coil surfaces, beginning at the point of entry of refrigerant into the coil.

At the point on the cooling coil (with no air blowing across it) where no more frost forms on the coil, we know that there is no more liquid refrigerant in the coil. That is, at this point in its travel through the cooling coil all of the liquid refrigerant that has been introduced has boiled (evaporated) to a gas. Now as all vapor, the refrigerant begins to absorb sensible heat and its temperature will increase. There are pressure increases at this point in the coil too, but they are insignificant.

In a refrigeration class demonstration, we learn that one could, given no other data, determine the proper refrigerant charge or better, the proper adjustment of an adjustable refrigerant metering device (Thermostatic expansion valve) by adjusting the refrigerant flow rate into the coil so that the frost line stops just before the end of the coil.

Normal cooling of building air at the cooling coil: In normal operation an air conditioning system is cooling air by moving it across a refrigerant-cooled “evaporator coil” or “cooling coil” in the air handler.

Dehumidification at the cooling coil: Cooling air passing over the coil also removes moisture from that air – a key factor in making indoor air comfortable in hot weather. (Photo at left of an iced-up cooling coil courtesy of Bill McNeill.)

Normally the moisture that’s removed from building air forms condensate on the surfaces of the cooling coil, runs down that surface to a collector pan, and is drained away.

Why frost or ice forms on a cooling coil in an active or in-use air handler

• The air flow is too slow across the cooling coil. The cause of this problem could be as simple as a dirty air filter or it could be crimped, disconnected ductwork or even improperly-sized ductwork. Don’t forget to check for a dirty blower fan itself – dirt can significantly cut airflow produced by the fan.
• The refrigerant is not being metered properly into the cooling coil, (too little is being released). A clogged capillary tube or a frozen, dirty, stuck thermostatic expansion valve can cause this trouble.Watch out: adding refrigerant to “fix” this problem by raising the compressor head pressure will indeed force more refrigerant through the system. But if/when that piece of crud blows out of the metering device too much refrigerant will flow back to the compressor, slugging it, perhaps destroying it when liquid refrigerant reaches the compressor internal parts.
• The refrigerant charge is too low. If there is a refrigerant leak, the first symptom may be coil icing; but later as refrigerant continues to be lost, all cooling may be lost and the coil will no longer be frosted or iced over. In our opinion it’s better to find and fix the refrigerant leak. See articles beginning at REFRIGERANTS.Below in this article you will see What Are the Common Causes & Repairs for Ice or Frost Build-up on an Air Conditioning Cooling Coil (the Evaporator Coil)?for our complete diagnostic list of causes and effects of cooling coil ice and frost blockage.Any or all of those conditions cause the level of refrigerant in the cooling coil to be too low; if there is some refrigerant but not enough the coil may become abnormally cold, freezing the condensate that forms on the cooling coil surface as moisture condenses out of air moving across the coil. This freezing condensate liquid can form frost and may build up into a coil icing problem or frost may appear on the cooling coil’s refrigerant suction line.

  When the surface of a cooling coil or suction line drops below 32 degF (say from too little refrigerant in the system or too little flow of warmer air across the cooling coil) frost formation is likely on that surface. Conversely, when the air conditioning system is working properly the surface temperatures on the cooling coil and on the refrigerant lines stay above 32 degF.

  In some installations the evaporator coil tend want to drop below 32 F even in normal operation, but air movement across the coil keeps its temperature higher, and thus avoids freezing. On some commercial refrigeration or air conditioning systems where lower temperatures are common, a defrost cycle is designed into the equipment. If an icing problem is occurring on commercial cooling systems, in addition to checking the refrigerant charge and air flow, the service technician will also check out the defrost cycle timer.

What Happens to the Ability of the Cooling System to Cool the Air When an Evaporator Coil Ices Up?

When the cooling coil has a nice thick ice build-up on its surface there will be no cool air produced by the air conditioning system at all. The fan runs, outside compressor/condenser run, but little or no air moves through the duct system. The page top photograph shows icing on the cooling coil and refrigerant lines exiting the coil inside air handler close to the evaporator coil even.

You might see ice formation on the suction line just outside of your air handler even though you cannot see the evaporator coil itself – on most residential air conditioning systems, the surfaces of the cooling coil are not readily accessible by the homeowner. But if you don’t see ice on the suction line, ice could still be present on and blocking air flow through the cooling coil.

The cooling coil, or evaporator coil is visible if the air handler is opened on some air conditioner units. At other installations the cooling coil is completely covered and can’t be seen at its location (say on a retrofit installation atop an existing hot air furnace) unless an inspection opening has been made (by cutting the steel and installing an access panel cover), or unless there is an opening that was made previously to install a humidifier in the same plenum chamber.

When an air conditioning system with a frost-blocked coil is turned off and allowed to warm up the ice on the coil melts and spills into the internal condensate collector tray in the air handler. Then when the air conditioner is re-started it may for a while produce cool air before becoming ice blocked again. If an air conditioning system behaves in this way coil icing is a possible explanation.

Frost build-up indicates an air flow or refrigerant problem. A blocked coil (by dirt) or a blower fan which has lost its ability to move air (such as a dirty squirrel cage fan) will reduce air movement across the coil and lead to frost build up there. We suspect this is the more common cause of this defect.

What Are the Common Causes & Repairs for Ice or Frost Build-up on an Air Conditioning Cooling Coil (the Evaporator Coil)?

As we introduced in the previous article, when the surface temperature of an air conditioning or refrigeration evaporator coil (cooling coil) drops below 32 degF or 0 degC, condensate forming on the coil surface begins to freeze, leading to sometimes some pretty weird behavior of the cooling system, none of it good.

1. Dirty air conditioning filter can block or reduce air flow across the cooling coil, leading to coil frost. This is the first component a homeowner should check since the fix: replace the air filter, is so easy.
2. Debris-blocked evaporator coils might lead to evaporator coil icing: When an air conditioning or refrigeration unit evaporator coil becomes sufficiently blocked with debris as to slow down the air flow enough, the coil may actually become so cold that the condensate forming on its surface freezes, completely blocking the coil. That’s because the rate of release of refrigerant into the evaporator coil was designed with an assumption of a sufficient volume of air moving across the coil to keep it from becoming too cold. . Dirty or debris-blocked evaporator coils are caused by running the air conditioning system without an air filter in place. The coil will need to be cleaned to get the system working again.
3. Damaged cooling coil fins can also lead to evaporator (cooling) coil freezing: when the coil cooling fins are bent and crushed sufficiently to block a significant portion of air flow across the coil, icing is likely.
4. Dirty blower fan blades or non-functioning blower fan assembly: an air handler blower unit that is not moving as much air as it should will be blowing too little air across the evaporator coil. This is a less likely but possible cause of frost build-up on the cooling coil.
5. Cooling coil fan (the blower in the air handler unit) has stopped working. A bad fan motor relay, a bad fan motor itself in the air handler unit (some call this the “evaporator fan”), lost (or someone turned off) electrical power to the air handler blower, or even a blocked fan blade or loose fan blade on motor shaft or a fan blade blocked by ice (rare in most residential air conditioning system designs), or a lost, or broken fan belt (if your motor is not a direct drive unit) can cause coil frost formation.The blower fan (air handler fan or evaporator coil fan) should run when your thermostat is calling for cooling. The motor could also be off on thermal overload or reset.  With electrical power to the blower unit off, see if the fan blade moves freely. If not the fan motor assembly needs repair or replacement.
6. Refrigerant loss or expansion valve problems might lead to cooling coil ice-ups: an improper charge or amount of refrigerant in the system can cause frost build-up on the evaporator or cooling coil. Too-little refrigerant can cause temperature in the coil to be abnormally low, leading to icing.Watch out: air conditioning refrigerant leaks are not normal and should be found and fixed. it’s better to find and fix a leak than to turn your leaky air conditioning system into a stop on your repairman’s regular refrigerant delivery route.
7. Thermostatic Expansion Valve malfunction: a bad TEV or capillary tube that is not metering refrigerant into the evaporator coil at the proper rate can cause frost build-up or icing on the evaporator coil or cooling coil.
8. Wall thermostat not working properly: a thermostat that fails to stop calling for cooling can lead to coil icing. When the set-temperature on the thermostat has been reached in the room where the thermostat is mounted, the thermostat should stop calling for cooling (or its switch should “open”. But wall thermostats are so simple that unless someone has damaged the thermostat or operated it in a very dirty environment we don’t find that the thermostat problem is a defect in the unit itself. More often it’s operator error: the thermostat is not set properly, or it is set to a low temperature that the cooling system simply can not reach.Watch out:Don’t just try quickly and repeatedly turning the thermostat up and down. Some air conditioner compressors may have trouble re-starting against the head pressure of refrigerant in the condenser unit. So if you keep switching the A/C system on and off the system may stop on a thermal reset. If you suspect you’ve caused this just leave the air conditioner off for 15 to 30 minutes and then turn it back on.
9. Just let the cooling coil ice melt? Watch out: advice you may find in some air conditioner repair articles such as “turn off the system and let the ice melt” are only partly correct. Turning off the air conditioning system for a sufficient length of time will indeed let the ice melt. But icing will simply return when the system is turned back on if you have not also found and fixed the cause of ice and frost formation in the system.

Why Frost or Ice May Appear on an Air Conditioning Refrigerant Suction Line

The ice formed here is at the low pressure inlet to an air conditioning compressor condenser unit. Similar ice may form at the evaporator coil (also called the cooling coil) or at the refrigerant suction line on the cooling coil at other end of the air conditioning system, as you can see in our iced-up air conditioning cooling coil photograph at the top of this page. [More photographs wanted].

Frost and ice can even form inside air conditioning duct work, leading to troublesome leaks into the building. This article explains locations and causes of condensate, frost or ice formation in air conditioning systems, air handlers, compressor/condensers, refrigerant lines, and in air ducts.

Several reasons can cause frost or ice formation not only on the cooling coil, but on the refrigerant suction lines at the equipment as well:

• Blocked air flow across the cooling coil, for example from a dirty air filter, collapsed duct insulation, crimped flex-duct, or similar problem.
• Improper refrigerant charge(too low a charge of refrigerant in the A/C system can, for a while, lead to too-low temperatures in the coil which will then cause frost or ice build-up on the suction line.Ultimately however, when there is simply little or no refrigerant left in the cooling system, temperature at the cooling coil will climb back up, the frost will disappear, and you’ll no longer have any cooling at all. In air conditioning service schools the instructor may demonstrate this effect by dynamically adjusting the amount of refrigerant in the cooling system as students watch the frost line extend down the suction line, then crawl back up to near the end of the cooling coil as the proper refrigerant charge amount is reached.

  Alternatively, on some cooling systems too much refrigerant can cause liquid refrigerant to flow past the cooling coil into the suction line,also causing icing.

• A malfunctioning refrigerant metering device like a bad thermal expansion valve (TEV). Conversely, a bad capillary tube (a more rudimentary refrigerant metering device found on refrigerators, dehumidifiers, and window air conditioners) won’t fail by passing too much refrigerant but it might fail to pass any refrigerant at all if it becomes blocked by debris or by a slug of oil in the system.
• A malfunctioning auto-defrost control or bad defrost timer control (less common on residential air conditioning systems)

Technical Note on Refrigerant Piping, HVAC Design and Heat Exchange Between the Low Pressure & High Pressure Refrigerant Lines: an HVAC economizer detail using refrigerant line brazing or soldering together

In some air conditioners or heat pumps at the point where the low-side suction line enters the compressor condenser unit the low-temperature (heat laden) vapor line (suction line) is soldered or brazed right next to and touching the high-temperature, high-pressure liquid refrigerant line. The purpose of this refrigerant piping detail is to act as a heat exchanger, to reduce the temperature of the liquid refrigerant that is going to enter the metering device (TEV or cap tube), gaining some benefit to system operation.

Other Causes of Ice Formation in Duct Work, What Happens, How to Stop and Prevent Air Conditioner System Ice Formation

In freezing climates such as New York where some homes route their top floor HVAC ducts along the attic floor, sometimes that ductwork is not well insulated and just as it gets too hot in summer (increasing the cost of air conditioning), in winter the same ducts become too cold, increasing heating costs. But something else funny can happen in homes with attic ducts that are used only for air conditioning.

One of our clients called us to investigate a claim that had resulted in litigation against the company who had installed a new roof on their home. The owner claimed that the roof was leaking. The roofer claimed that the roof was perfect. What was curious was that the roof “leaked” only at the end of winter, and at times when there had been no rain and when there was no melting snow on the rooftop.

What we observed was the following causes of ice in the air ducts:

• There were leak stains at most of the top floor air conditioning ceiling-mounted supply registers.
• There were leak stains at the top floor ceiling mounted return air register
• The home had hot water baseboard heating and used its ductwork only for air conditioning during the summer
• The home had a problem of chronic basement water entry and was in general pretty damp, even in winter
• Inspecting the home’s attic and the duct work in the attic I was astonished to find that in the dead of winter the ducts had about 2″ of solid ice in the bottom of the ductwork! Ice was thickest closest to the supply or return registers and was thinnest in the middle of the duct runs
• [Have you guessed yet?]
• Inspecting back out of the attic and at the supply registers on the second floor, all of them were open – which is pretty common – few people think to close off un-used air conditioning supply registers in winter.

The duct ice problem was occurring because warm moist air was circulating by convection during winter, rising up into both the supply and return registers, flowing through the duct work, and leaking out of an open air handler. As the warm moist air entered the attic, the ducts were absolutely freezing cold. Moisture first condensed, then formed ice inside the duct system.

Ice accumulated in the duct system throughout the winter a little at a time, until it was several inches thick.

When the weather warmed all that ice in the ducts melted and leaked back out into the upper floor in a stunning flood. The owners, who were not thinking particularly clearly about whether or not it was raining or whether or not there was melting snow on the roof, saw that it was “raining inside” out of their air conditioning ducts and through other ceiling locations (since the ducts were not water tight there was leakage out of the ducts at other areas besides just at the supply and return air registers.

The solution to this problem had two components:

1. Close off all of the ceiling mounted supply and return air ducts (at the registers) at the end of the air conditioning season since they were not needed for heating. This stopped the flow by convection movement of warm house air into the un-used A/C duct system. (Warm air rises up into a cool space.)
2. Identify the sources of high indoor moisture (such as basement water entry) and fix them so that the house is not abnormally damp. (Stop providing high levels of moisture un-wanted in house air.)

The roofing contractor was happy with this solution and the building owner was relieved as well. Perhaps because their roof had previously been leaking, before it was replaced, when they saw water coming through their top floor ceilings they thought that it was still leaking. Of course the ice in ducts problem won’t occur in homes which use the same duct system for winter heating, nor will it occur in climates where freezing weather is uncommon, though we still might see some surprising in-duct condensation in some cases.

FROST BUILD-UP – Frost Build-up on the Evaporator Coil in an Air Conditioner

The ice or frost formed on a cooling coil in an air conditioner air handler unit is usually caused by an improper refrigerant charge, possibly by inadequate air flow across the cooling coil, or by a thermostatic expansion valve (TEV) or other air conditioner or heat pump control defect.

Ice blocks air flow through the coil, thus reducing air conditioner output; if the ice formation is extreme nearly all of the airflow across the coil is blocked and the air conditioner system runs but does not produce cool air flowing into the occupied space.

Frost and ice can also form on refrigerant tubing at other locations, and frost and ice can form inside air conditioning duct work itself, leading to troublesome leaks into the building.

Details of what causes frost on air conditioning equipment, what problems that creates, and how to diagnose and repair icing or frost on cooling coils or other air conditioner parts are provided at FROST BUILD-UP on AIR CONDITIONER COILS. There we discuss locations and causes of condensate, frost or ice formation in air conditioning systems, air handlers, compressor/condensers, refrigerant lines, and in air ducts.

Note that frost formation at some cooling coils (not air conditioners or dehumidifiers) may be normal. We discuss frosting and non-frosting cooling coil types and coil defrosting methods further at Frosting vs. Non-Frosting Types of Evaporator Coils

These Advanced Design Guidelines have been developed by the New Buildings Institute in cooperation with Southern California Gas Company to assist designers, program planners, and evaluators to make informed decisions on the application and cost-effectiveness of gas engine-driven cooling.
There are two basic types of gas chillers: engine-driven systems and absorption systems. This Guideline deals specifically with gas engine-driven systems.
These Guidelines are intended to be a step toward a comprehensive approach to design specifications, which encompasses the full range of efficiency options for a building.
This Advanced Design Guideline is based on careful evaluation and analysis of gas engine-driven cooling to determine when it is appropriate, how it is best implemented, how cost effective it is, and how its energy savings are described.
These Guidelines describe efficiency measures that are more advanced than standard practice, yet still cost effective in appropriate applications.
Design Guidelines are used by individuals and organizations interested in making buildings more energy efficient.
They provide the technical basis for defining efficiency measures used in individual building projects, in voluntary energy efficiency programs, and in market transformation programs.
It should be remembered that this Guideline document deals primarily with the comparison of a single efficiency measure and its baseline.
This means that the analysis assumes that all other features of the building are fixed.
This is done primarily for clarity of the analysis, and allows one to focus on the advantages and economics of the single measure.
In reality, most new building design situations involve multiple energy efficiency options.
The cost effectiveness of one measure is often influenced by other measures.
For example, increases in building envelope insulation can often reduce HVAC loads enough to reduce the sizing requirements for the heating and cooling equipment.
It is not uncommon for the cost savings from smaller equipment to offset increased insulation costs.
It is beyond the scope of this Guideline to attempt to address the interactions between measures, especially because these interactions can cover a huge range of options depending on the climate, the local energy costs, the building, and its systems.
Nevertheless, the New Buildings Institute recommends that building designers give careful consideration to measure interactions and to integrated systems design.
This Guideline can provide the starting point by providing insight into the performance of one measure.

Remember to inspect the cooling coil from the incoming-air side – the side of the coil facing the blower fan assembly. That’s because any dirt or debris entering the coil will come principally from this direction. If you inspect the wrong side of the coil it may look perfectly clean even though it is totally blocked by debris on its other surface. DIRTY COOLING COIL has photos of just how blocked a cooling coil can become in an air conditioner or heat pump.

Here are some common defects to look for at the evaporator coil (cooling coil) in an air conditioner or heat pump:

• Dirt or debris blocking air flow through the coil (DIRTY COOLING COIL)
• Ice or frost formation blocking air flow through the coil (FROST BUILD-UP on AIR CONDITIONER COILS)
• Damaged cooling / evaporator coil fins over more than 10% of the coil surface, blocking air flow (shown in our photo at left in this case, the damage is to a condensing coil, not an evaporator coil). Small areas of damaged cooling fins can be straightened and cleaned-up using a cooling coil comb. Cooling coils with extensive physical damage such as shown in our photograph need to be replaced.
• Evidence of refrigerant leaks (visual evidence may include stains from refrigerant oil left at the point of leakage) (REFRIGERANT LEAK DETECTION)
• Evidence of mold growth on organic debris on the coil or elsewhere in the blower compartment (Mold Growth in Air Handlers)
• Presence of unusual materials on the coil surface such as rodent debris, bird feathers and debris, fiberglass insulation, large trash fragments like paper or leaves confirming a duct or air filter problem. Some of these may indicate potentially serious health risks such as rodent or bird feces and debris which risk bacterial and viral hazards in building air. (Leaks, Rodents In Air Handlers)
• Obvious coil-to-air-handler size mismatch of an add-on cooling coil onto an existing warm air system (ADDING A/C: RETROFIT SIZING)
• Evaporator coil or cooling leaks or holes: if an evaporator coil is leaking (or also if the condensing coil is leaking) you’ll find out pretty quickly as refrigerant will be lost and the cooling system will stop providing cool air. You’ll need expert diagnosis by an HVAC service technician.
  • A lot depends on where the refrigerant leak has occurred and what caused the leak. If the cooling coil has a single point leak caused by some mechanical damage (one of our readers accidentally drilled a hole in his coil while trying to drill a drain hole in his air handler), it may be possible to find the hole and repair it using silver solder.
  • If the refrigerant leak is in copper tubing anywhere in the cooling or heat pump system that is not too close to an evaporator coil or condensing coil, it should be possible to solder a repair, then evacuate and recharge the cooling system.
  • If the refrigerant leak is in copper tubing in or close to the cooling coil (or in a condensing coil) a solder repair is hard to complete because the heat of the soldering process tends to de-solder other nearby connections. It might be possible if the technician is very expert and if s/he knows how to keep nearby surfaces cooled (we’ve used a wet rag).
  • If the refrigerant leak is in an aluminum part, soldering aluminum is more tricky and may not be feasible. Ordinary procedures using a torch, for example, just melt the aluminum. Expert welders use inert gas welding methods.
  • If the refrigerant leak is due to severe corrosion anywhere in an HVAC system we’re not optimistic that a solder repair is possible. The conditions that caused a corrosion-related leak are likely to have thinned and weakened other parts. The cost of an attempted repair may be wasted.
  • Replacement of the cooling coil (or condensing coil) is more often going to be recommended by your HVAC technician because of these difficulties.

Temperature measurements at the cooling coil: see OPERATING TEMPERATURES for a discussion of where and how air temperature measurements are made to diagnose cooling coil or other air conditioner operating problems.

Below we introduce some of the more common air conditioner or heat pump cooling coil or evaporator coil defects and repairs.

Air flow requirements across the air conditioning evaporator coil: if airflow is weak for any reason (dirty coil, duct system defects, blower fan defects, dirty blower squirrel cage fan), the air conditioning system will not operate properly. Some experts write that there should be between 350 and 400 cubic feet of air per minute (CFM) moving across the evaporator (cooling) coil for each ton of air conditioner capacity.

One ton of cooling or heating capacity = 12,000 BTUH so if your AC unit or heat pump is a 24,000 BTUH unit it is a “two ton” unit and needs to see 700 to 800 CFM of air across the evaporator coil.

Some home inspectors and air conditioning service technicians carry a small airflow meter that can actually measure this number with fair accuracy. (The same tool is nice for comparing air flow and balancing air flow at various building supply ducts and registers.

Rangkuman Diskusi Mailing List Migas Indonesia – Mei 2003

Pertanyaan : Robikhun

Membaca salah satu artikel di majalah OTOMOTIF terbaru ada hal yang menarik
yakni gagasan mahasiswa ITS untuk membuat AC yang dipasang pada sepeda
motor. Berbeda dengan AC mobil yang menggunakan siklus refrigerasi yang
sudah dikenal dalam ilmu termodinamika, AC motor hanya menggunakan
sebagian siklus. Untuk lebih jelasnya lihat artikel berikut. <<AC Motor2.ZIP>>
Nah pertanyaannya, bagaimana penjelasan secara termodinamika mengenai
fenomena ini? Saya meragukan konsep pemisah udara bertemperatur rendah
dan udara bertemperatur tinggi. Bukankah energi akan berpindah dari temperatur
tinggi ke temperatur rendah?

Artikel AC Motor2.ZIP (402 KB) bisa di-download

Tanggapan 1 : Mual Sihombing

Sesuai dengan definisinya, refrigeran adalah fluida kerja pada sistem refrigerasi, pengkondisian udara, dan heat pump. Refrigeran berfungsi untuk menyerap kalor dari satu area dan membuangnya ke area lain. Jadi, sepanjang suatu zat dapat berfungsi sesuai dengan definisi di atas maka zat tersebut secara teori dapat digunakan sebagai refrigeran.

Namun selain itu ada sejumlah besar sifat fisis dan kimiawi yang perlu dipertimbangkan dalam pemilihan refrigeran, misalnya : kestabilan kimia, titik didih, titik beku, titik kritis, kalor laten penguapan, apakah zat tersebut mudah terbakar, beracun atau tidak, kesesuaian dengan komponen mesin, duit, dsb.

Udara dapat dijadikan sebagai refrigeran (untuk lebih jelasnya Bapak dapat baca di ASHRAE standar 34) dan hal ini sudah lama dipakai pada pendinginan pesawat udara.

Berbeda dengan siklus refrigerasi mekanik kompresi uap yang menggunakan
kompresor, evaporator, kondenser, dan katup ekspansi, maka sistem refrigerasi dengan refrigeran udara (gas) terdiri dari empat komponen yaitu 2 buah penukar kalor, turbin, dan kompresor. Prinsip kerja sistem refrigerasi gas pada pesawat udara – yang menggunakan siklus terbuka – dapat dijelaskan sebagai berikut :
Udara luar dikompres oleh kompresor sehingga tekanan dan temperaturnya naik.Udara dengan tekanan dan temperatur tinggi ini kemudian didinginkan oleh udara sekeliling sehingga tekanan dan temperaturnya turun sebelum kemudian diekspansikan oleh turbin. Udara yang diekspansikan di dalam turbin akan mengalami penurunan temperatur sehingga menjadi dingin. Udara dingin inilah yang didistribusikan ke kabin-kabin.

Sistem refrigerasi gas memiliki COP (Coefficient of Performances) yang lebih rendah dari pada sistem refrigerasi mekanik kompresi uap, namun juga memiliki sejumlah keuntungan: lebih sederhana, ringan, sehingga sesuai untuk pesawat udara.

Silahkan menambahkan.

Tanggapan 2 : Muchlis N

Sepertinya didalam ACT terjadi proses seperti pada gas to gas heat exchanger. Secara termodinamis hal ini bisa terjadi.

- Jadi walaupun hanya ada 1 inlet gas, saluran outletnya ada 2. Artinya di dalam alat tersebut ada split aliran menjadi 2 didalam tabung ACT yang konstruksinya dirahasiakan itu..
- Salah satu aliran tetap dibiarkan bertekanan tinggi, dan satu aliran yang lain diturunkan tekanannya ke atmosfir (expansi).
- Aliran yang bertekanan lebih rendah akan memiliki temperatur yang lebih rendah sehingga mampu mendinginkan aliran yang bertekanan tinggi (penurunan tekanan mengakibatkan penurunan suhu). Akibatnya ada kalor yang terbuang dari aliran bertekanan tinggi.
- Kemudian aliran bertekanan tinggi yang sudah didinginkan ini kemudian dialirkan ke dalam jaket, tekanannya turun menjadi atmosferis sehingga menjadi lebih dingin lagi.

Tetapi karena keterbatasan kemampuan refrigeran, maka temperatur dinginnya hanya sekitar 24 oC.

Apakah kita rela mengorbankan tarikan motor hanya untuk menurunkan suhu jaket kita menjadi 24 oC. Mendingan gak usah pake jaket aja, kan dingin juga……..kecuali pas kena macet

Tanggapan 3 : Ary Retmono

Saya rada nggak mudheng dg penjelasannya Bang Mual:

Udara di luar pesawat (apalagi kalau sdh di cruising altitude) ‘kan bisa mencapai minus 43degC (walau terbang di atas Gurun Sahara saat”summer”), lha kenapa ya, koq nggak langsung dimanfaatkan untukmendinginkan udara di dalam cabin, ketimbang harus dikompres-kompresdulu?
Tanggapan 4 : Haryo

Mas Ary,
Kalo temperaute 43 C langsung di tiupkan ke kabin, apa gak jadi daging beku
semua penumpangnya?

Waktu kuliah dulu saya sempat dikenalkan istilah “bleed air” yang dimanfaatkan untuk pendinginan udara di kabin.

Kalau tidak salah ingat, bleed air adalah udara yang “dibocorkan” dari hasil
kompresi mesin pesawat. Udara yang “hangat” ini yang kemudian dihembuskan
ke kabin.

Kalo menurut saya, yang awam tentang system refrigerasi, system seperti di
atas saja sudah cukup. Apa perlu “accessories” lain?

Mohon penjelasan dari yang familiar dengan system refrigerasi, khususnya
untuk pesawat.
Tanggapan 5 : Harsono

Ikutan menanggapi ya mas Ary.
Saya jadi ingat pernah belajar Cabin Pressure Control System, pada dasarnya
pengaturan kondisi kabin itu dikondisikan pada human comfort. Ya sebisa
mungkin tekanan dalam cabin 1 atm, suhunya pada suhu ruang normal dan
tentunya komposisi O2 dalam cabin juga mencukupi untuk penumpang. Sementara
semakin tinggi altitudenya tekanan udara semakin rendah, O2 semakin tipis
dan suhu makin rendah. Jadi selain ada pengaturan suhu ya tentunya ada
pengaturan tekanan dan penambahan O2 selanjutnya perbedaan tekanan di luar
dan didalam cabin akan menentukan kekuatan material si cabin itu.
Mohon maaf menyimpang dari tema refrigran.

This book provides students with the basic skills they will need to prepare a wide range of piping drawings. It presents a step-by-step approach to the basic fundamentals students will need to begin a successful career in industrial drafting and design. Chapter One gives a quick overview of the many opportunities in drafting and design for those who master the basic skills presented in the following chapters. Then each chapter builds on the preceding one. It is necessary therefore to master the concepts in a given chapter before going on to the next one. Each chapter concludes with exercises and questions designed to help students review and practice the concepts presented in that chapter.

Today, engineers still have a moral, legal, and ethical responsibility to protect the public in professional practice and in design of products, buildings, processes, equipment, work, and workplaces. The importance of safety in engineering education remains a concern for most engineering degree programs. The need for safety specialists to understand basic technical fundamentals essential in hazard recognition, evaluation, and control continues. As a result, there is still a need for this book.

The laws, regulations, standards, and standard of practice in safety and health continue to change on a regular basis. As soon as a book is complete or updated, it is likely to be out of date in certain regulatory areas. The reader should recognize this type of change and consult government and voluntary standards to ensure compliance with current requirements.

Technology continues to change. Computer technology has changed the toolbox for nearly every professional field, and it impacts safety practice as well. Since the first edition was published, the Internet has become an integral part of professional practice, business and business transactions, and many other elements of daily life. Although the explosion in availability of information continues, one must be able to sort out valid, quality information and reliable information sources from those sources that are not. It is far easier today to find information as well as misinformation on a wide variety of safety issues.

The overall field of safety has changed. One significant trend is the continued growth in education of those practicing at the professional level. More individuals than ever who specialize in safety have advanced degrees. At the same time, many employers have achieved significant improvements in safety performance by moving safety knowledge and skills deeper into their organizations and workgroups. There seems to be a growing interest among people from other areas of work experience in finding a professional home in the broad safety field. Another trend is the rapid convergence of several related areas of practice. Two decades ago, safety, industrial hygiene, environmental science and engineering, environmental health, ergonomics, fire protection, and other areas of practice often were isolated from each other. Today, many of these have converged into a single organizational unit for an employer, and many individuals-regardless of their original backgrounds- have responsibility for many of these areas simultaneously. The overall impact is a change in what safety and health specialist do.

The original goal for this book was to help engineers and others gain a broad, quick overview of safety and health practices and to identify some of the detailed resources that may provide expanded help with applications. One of the most valued results of having written this book in the first place is having people who I have never met express appreciation for the assistance it provided them in their professional development. Many have told me that it helped them to understand what safety and health practice is about. It is rewarding to know that a personal project has assisted others professionally.

Microsoft Excel is a powerful spreadsheet program; in fact, it’s the most widely used spreadsheet program worldwide, but Excel is a lot more than just a spreadsheet program.

Unknown to many users, Excel is also a sophisticated platform for development of custom applications. Lurking behind its mild-mannered spreadsheet disguise is a powerful and full-featured programming language called Visual Basic for Applications (VBA).

If you have recorded and played back an Excel macro, you have used VBA-perhaps without being aware of it. There’s much more to VBA programming than recording macros, however. Nearly any user can write VBA programs to perform a wide variety of tasks in Excel, ranging from the simple, such as automating financial calculations, to the complex, such as creating a data entry system with custom forms and data validation. Unfortunately, many users shy away from taking advantage of Excel’s programmability because it seems too complicated, and they cannot find a good source of information to guide them through the learning process. Excel programming can be somewhat complicated, which is unavoidable for such a powerful tool, but the truth is that almost any reasonably computer-literate person can learn how to program in Excel. That’s where this book comes in handy.

Who Should Read This Book

This book is aimed at anyone who wants to use programming to improve his or her Excel skills. Perhaps you only want to write programs for your own use, or maybe you need to create Excel programs for use by your coworkers. In either situation, this book is aimed at you.

The book was written specifically with the non specialist in mind. You do not need to have any programming knowledge or experience to use this book because everything from square one is explained. Of course, if you do have some programming experience, it will not hurt, but the important point is that such experience is not required.

The 2007 Microsoft Office system goes far beyond previous releases in helping you run your business and expand your reach. More than a set of tools for the everyday essentials (word processing, spreadsheet, communication, and more), the 2007 release offers a whole set of integrated new capabilities that support you in marketing and sales functions; offer professional templates for high quality presentations and documents; and assist you in more efficient, effective, and-in some cases, instant-communications.

Refrigeration and its application is met in almost every branch of industry, so that practitioners in other fields find that they have to become aware of its principles, uses and limitations. This book aims to introduce students and professionals in other disciplines to the fundamentals of the subject, without involving the reader too deeply in theory. The subject matter is laid out in logical order and covers the main uses and types of equipment. In the ten years since the last edition there have been major changes in the choice of refrigerants due to environmental factors and an additional chapter is introduced to reflect this. This issue is on-going and new developments will appear over the next ten years. This issue has also affected servicing and maintenance of refrigeration equipment and there is an increased pressure to improve efficiency in the reduction of energy use. This edition reflects these issues, whilst maintaining links with the past for users of existing plant and systems. There have also been changes in packaged air-conditioning equipment and this has been introduced to the relevant sections. The book gives worked examples of many practical applications and shows options that are available for the solution of problems in mechanical cooling systems. It is not possible for these pages to contain enough information to design a complete refrigeration system. The design principles are outlined. Finally, the author wishes to acknowledge help and guidance from colleagues in the industry, in particular to Bitzer for the information on new refrigerants.