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.

The purpose of the compressor in a refrigeration system is to raise the pressure of the refrigerant vapor from evaporator pressure to condensing pressure. It delivers the refrigerant vapor to the condenser at a pressure and temperature at which the condensing process can be readily accomplished, at the temperature of the air or other fluid used for condensing.