Refrigeration compressor sizing calculator
What Compressor Size do I Need?
A general knowledge of piping practices is required to make an intelligent choice. Normally, each of the system components has a stub connection of a specific pipe size. Using the stub connection size as a guide to determine which pipe size to use is generally not a good practice.
Equipment manufacturers design their stub connections for the average or most common pipe size used. The actual pipe size needed may be larger or smaller. The Suction Line Of the major sections of pipe, the suction line is the most critical to size properly. Generally, the suction line is sized for a minimum pressure drop through the line and a minimum velocity in order to ensure good oil return to the compressor.
If the pipe chosen is too large, the velocity of the refrigerant flow will be reduced. Since the refrigerant is in a gaseous state in the suction line, it does not mix well with the refrigerant oil.
The velocity of the gaseous refrigerant helps to push the oil along the suction line. If the velocity is too low, the oil will collect in the suction line in the evaporator. This will lead to a shortage of oil at the compressor that can cause damage.
If the suction line is too small, oil return will not be a problem.
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However, there may be an excessive pressure drop through the suction line. Deciding which pipe size to use for the suction line is generally a compromise between ensuring good oil return and maintaining a minimum pressure drop through the line. Discharge and Liquid Lines It is also important to correctly size the discharge and liquid lines.
However, in the discharge line the refrigerant is traveling at a higher velocity, the oil is pushed along, and the pipe size is not as critical. In the liquid line, since the refrigerant is in its liquid form, it tends to mix well with the refrigerant and is carried along easily. Most manufacturers will include recommended pipe sizes with their installation and service literature.
Technicians need to refer to this material when piping in any component.CoolingLoad
If the original installation and service literature is not available, there are universal tables and charts available to aid in choosing the right pipe size. This will always ensure the right size is chosen for the job and that the system will function properly in its design refrigeration capacity.
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One of the biggest challenges is to correctly size your new air compressor. Similarly to everything else, new compressors available on the market are more efficient and employ better technology, therefore you have to understand the application and usage to size the machine correctly. Choosing the wrong air compressor for your facility can lead to problems with production and or increased costs due to wasted energy.
Understanding the flow and pressure requirements for your facility is key when choosing an air compressor. Pressure and flow are two very common terms used when discussing compressed air systems. Pressure can be measured in pounds per square inch psior bar metric measure of pressure.
To think of this in simpler terms, pressure refers to the amount of force needed to perform certain amount of work at any given point in time. A simple example of pressure and how it works, is to imagine moving a wooden block across a table.
In the illustration below, it shows that using 75 psi of compressed air is not enough force to move the block, but psi of pressure has the ability to move the wooden block the desired distance.
The air compressor has to provide enough pressure to perform a given task in this case it was to move a wooden block. Per illustration below, if psi is required to move the block, anything less than that will not accomplish the task. It is important to understand what pressure is needed in order to size the compressor properly, otherwise you will be faced with problems, similar to illustration below where lower pressure was not able to move the wooden block, or perform the job.
In simpler terms, flow is the ability of the compressor to continue performing a task within an acceptable time frame. The amount of flow required is determined by the length of time needed to complete a given task. Let us consider the wooden block example to explain this further. To move a wooden block a certain distance every hour will require less flow and can be achieved with a smaller compressor and a storage tank.
The compressor will cycle on and off and refill the storage tank for the next time the wooden block is required to move.
However, if the wooden block has to be moved constantly within a given time frame, a larger flow of air or CFM with continuous flow will be needed, thus requiring a larger compressor. If the flow is insufficient, the process will require frequent breaks while the compressor builds up pressure in the reserve tank, therefore indicating that the compressor might be undersized.
Ultimately, when you are looking to supply enough compressed air for a given application, it is important to consider the amount of compressed air flow CFM needed at a specific pressure PSI required for the process to work properly.
One of the ways to find out the total flow needed is to contact the manufacturer of the equipment that uses compressed air and request data sheets with desired information. It is important to keep in mind that rotary screw air compressors tend to put out more flow per kW or HP than piston compressors.
To summarize, pressure PSI is determined by the job you are performing, while flow CFM will require the understanding of how frequently the job has to be done, or how many jobs you are performing at the same time. It is important to understand that under sizing a compressor will result in pressure drops and inability to complete a task, while oversizing the unit can lead to future mechanical problems and potential failure of the compressor. If you are unsure on how to size your new compressor for existing or new application, always contact a compressed air sales professional for an audit.
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You can use the Carnot Equation to solve for your theoretical best efficiency. Once you know that, you deturmine what capacity you need. From that point, you can go on to sizing your compressor, working fluid, operating pressure, condenser, evaporator, air flow rates, etc. Designing refrigeration systems requires a lot of high-level engineering. I recommend investigating your original objective, researching refrigeration systems, and posting back here with a new question if you need help at that point.
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How to size a refrigeration compressor based on an evaporator size?
Asked 3 years, 7 months ago. Active 1 month ago. Viewed 5k times. In order for such questions to be answered in this site, we need you to add details describing the precise problem you're having. What have you tried to solve this yourself? Please edit your question to include this information. Active Oldest Votes.
Engineering Stack Exchange is a question and answer site for professionals and students of engineering. It only takes a minute to sign up. You can use the Carnot Equation to solve for your theoretical best efficiency. Once you know that, you deturmine what capacity you need. From that point, you can go on to sizing your compressor, working fluid, operating pressure, condenser, evaporator, air flow rates, etc. Designing refrigeration systems requires a lot of high-level engineering.
I recommend investigating your original objective, researching refrigeration systems, and posting back here with a new question if you need help at that point. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How to size a refrigeration compressor based on an evaporator size? Ask Question. Asked 3 years, 7 months ago.
Active 1 month ago. Viewed 5k times. In order for such questions to be answered in this site, we need you to add details describing the precise problem you're having. What have you tried to solve this yourself? Please edit your question to include this information. Active Oldest Votes. Sign up or log in Sign up using Google.
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A cold room is used to store perishable goods such as meat and vegetables to slow down their deterioration and preserve them as fresh as possible for as long as possible. Heat accelerates their deterioration so the products are cooled down by removing the heat.
To remove the heat we use a refrigeration system as this allows accurate and automatic control of the temperature to preserve the goods for as long as possible. To remove the heat we need to know what the cooling load will be. The cooling load varies throughout the day so in most cases the average cooling load is calculated and the refrigeration capacity is calculated to suit this.
This is the thermal energy transferred through the roof, walls and floor into the cold room. Heat always flows from hot to cold and the interior of the cold room is obviously a lot colder than its surroundings, so heat is always trying to enter the space because of that difference in temperature. If the cold store is exposed to direct sunlight then the heat transfer will be higher so an additional correction will need to be applied to allow for this.
This accounts for the heat that is introduced into the cold room when new products enter. Its also the energy required to cool, freeze and further cool after freezing. During this time energy is used but you will not see a temperature change while the product changes between a state of liquid and ice.
There is additional energy required to further chill this food down below the freezing point which is again sensible heat. You also need to account for the packaging as this will inherently be cooled also. This is the heat given off by people working in the cold room, the lighting and equipment such as fork lifts trucks etc.
For this we want to know the rating of the fan motors and estimate how long they will run for each day, then we want to also account for any heat transferred into the space from defrosting the evaporator. This occurs when the door opens so there is a transfer of heat into the space through the air. The other consideration is ventilation.
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Lets consider a simplified example of a cooling load calculation for a cold room. Just to note the manufacturer should tell you what the u value is for the insulation panels, if not, then you will need to calculate this. Next we will calculate the cooling load from the product exchange, that being the heat brought into the cold room from new products which are at a higher temperature.
Next we calculate the product respiration, this is the heat generated by living products such as fruit and vegetables. If you were to calculate for a critical load you should use greater precision.
Then we can calculate the heat generated by the lighting, this is fairly simple to do and we can use the formula. For the total internal load we then just sum the people load 2. Now we can calculate the heat generation of the fan motors in the evaporator. For this we can the use the formula of:. Now we will calculate the heat load caused by defrosting the evaporator.
In this example our cold room uses an electric heating element rated at 1. The total equipment load is then the fan heat load 8. Now we need to calculate the heat load from air infiltration.