(Contuation of earlier article will appear after this post!)
Sizing an air conditioner
Recently I read in an Indian HVAC magazine the following.
0.5 TR AC for upto 250 sft(25 SQM),
1 TR Ac for upto 550 sft(55 sqm), and
2 TR for upto 1400 sft (140 sqm).
Is it not very surprising? For, this one seems to be addressing residences!
Even in a multistoried complex, with all the floors conditioned, these figures are going to be impossible to achieve.
I feel the data would be correct if it reads like:
With Indian ambient conditions, 0.5 TR is ruled out for many applications. Hence,
1 TR for up to 120-200sft,
1.5 TR for up to 150-250 sft &
2 TR for upto 200-300 sft!
depending upon other factors.
Saturday, December 30, 2006
How to run AC units efficiently at home or office? PART 6
Now you have selected and installed a inverter unit. Setting up the required temperature is your job, as you only must know what you want!
After this is over, let us assume that you have just entered the room and switched on the unit. As the room was unconditioned till then, the difference between the set point and room temp at that time will be high. Sensing this, the system sets itself to produce maximum cooling. The temp starts approaching the set point. As soon as the room temperature is reached, the compressor does not cut off now. Some heat continues to flow into the room constantly, the compressor runs at a matching speed just producing that much of cooling only. So there is no questioning of over cooling. We have eliminated the requirement for thermostat having to perform two opposing functions at a single set point. It simply keeps relaying the room temperature only to the control system. Now that the need for more or faster cooling is over, the compressor receives a command to reduce its speed. Thus the room temperature just stays where you want it to stay with no fluctuations or cycling. As there is no frequent staring and stopping of compressor, the power supply also does not get disturbed. Thus the unit meets the cooling demand as per needs, producing more at the beginning till the room is fully cooled, and then adjusting its speed in line with the room load.
Imagine this type of units being used by all. Will it not be nice? The energy demand will be reduced especially in nights, and voltage as a result will stay more stable! Government can relax, having solved the problem of shortage of electricity as well as avoiding fluctuations in voltages!
Thus having reduced the momentary demand to lower values from users of such small capacity clients, how can this benefit be passed on to the industry or commercial sector?
We will see it in our next topic.
After this is over, let us assume that you have just entered the room and switched on the unit. As the room was unconditioned till then, the difference between the set point and room temp at that time will be high. Sensing this, the system sets itself to produce maximum cooling. The temp starts approaching the set point. As soon as the room temperature is reached, the compressor does not cut off now. Some heat continues to flow into the room constantly, the compressor runs at a matching speed just producing that much of cooling only. So there is no questioning of over cooling. We have eliminated the requirement for thermostat having to perform two opposing functions at a single set point. It simply keeps relaying the room temperature only to the control system. Now that the need for more or faster cooling is over, the compressor receives a command to reduce its speed. Thus the room temperature just stays where you want it to stay with no fluctuations or cycling. As there is no frequent staring and stopping of compressor, the power supply also does not get disturbed. Thus the unit meets the cooling demand as per needs, producing more at the beginning till the room is fully cooled, and then adjusting its speed in line with the room load.
Imagine this type of units being used by all. Will it not be nice? The energy demand will be reduced especially in nights, and voltage as a result will stay more stable! Government can relax, having solved the problem of shortage of electricity as well as avoiding fluctuations in voltages!
Thus having reduced the momentary demand to lower values from users of such small capacity clients, how can this benefit be passed on to the industry or commercial sector?
We will see it in our next topic.
How to run AC units efficiently at home or office? PART 5
These new units are called DC INVERTER AC units, with rotary or scroll compressors. We are limiting our attention to rotary compressors that is considered better for the lower capacities.
The very basic difference, from your point of view is that, these systems produce exactly the amount of cooling required by a room, and not a fixed cooling having no relevance to the room load like the earlier units discussed above.
It is enough for you to know this much.
They achieve this by running the compressor at varying speeds, and not at a fixed speed. Since DC motors can be better controlled, they employ a DC motor instead of AC motors that is adopted in earlier AC units.
How does it satisfy YOU?
Wait for the next part.
The very basic difference, from your point of view is that, these systems produce exactly the amount of cooling required by a room, and not a fixed cooling having no relevance to the room load like the earlier units discussed above.
It is enough for you to know this much.
They achieve this by running the compressor at varying speeds, and not at a fixed speed. Since DC motors can be better controlled, they employ a DC motor instead of AC motors that is adopted in earlier AC units.
How does it satisfy YOU?
Wait for the next part.
How to run AC units efficiently at home or office? PART 4
(For the time being we are ignoring the existence of Inverter type units)
The heat loads are normally estimated for the worst ambient conditions and units are selected. However the actual load seldom remains the same because the ambient temperature keeps varying. However once a unit is selected and installed, it always tries to produce its full capacity possible at that ambient condition, irrespective of the actual cooling required. Though there is a thermostat, the room goes through a cyclic cooling, which makes the occupant feel uncomfortable. The cyclic process is unavoidable for a few reasons. First, the rate at which cooling is produced is never equal to the rate which heat enters the room. Hence the unbalance always produces un-comfortableness. Second, the thermostat being a mechanical device requires two end points to cut off the compressor and restart it a little latter. When the cutting off takes place, say at 24 ˚ C, then the next minute theoretically it would have to restart because the temperature would have risen. But in practice it is allowed to do so, as otherwise the compressor starts cycling, or repeatedly starts and stops. This not only disturbs the power supply systems characteristics, but also the life of the compressor itself! Also practically it is impossible to produce a device that does two opposing functions at a single point, namely cutting off and restarting. Hence a gap is given in the device to function, which is referred to as ‘differential’. Either it is allowed to overcool and restart at the set point or cuts off at the set point but restarts at a slightly higher temperature!
In addition the human body is so sensitive to temperature, that at the same indoor temperature, it feels differently during summer and winter. (i.e) You may feel very comfortable at 22 ˚ C during summer, but during winter a slightly higher temperature will feel more comfortable. The poor combination of your compressor and thermostat do not understand this.
So as long as you have installed an equipments that produces constant cooling irrespective of the load, you have to set your preferred temperature in the thermostat and accept a cyclic nature of indoor temperature and be comfortable with that!
Now enter the new variety of, not only ENERGY EFFICIENT AC units, but also units that can think like you!
The heat loads are normally estimated for the worst ambient conditions and units are selected. However the actual load seldom remains the same because the ambient temperature keeps varying. However once a unit is selected and installed, it always tries to produce its full capacity possible at that ambient condition, irrespective of the actual cooling required. Though there is a thermostat, the room goes through a cyclic cooling, which makes the occupant feel uncomfortable. The cyclic process is unavoidable for a few reasons. First, the rate at which cooling is produced is never equal to the rate which heat enters the room. Hence the unbalance always produces un-comfortableness. Second, the thermostat being a mechanical device requires two end points to cut off the compressor and restart it a little latter. When the cutting off takes place, say at 24 ˚ C, then the next minute theoretically it would have to restart because the temperature would have risen. But in practice it is allowed to do so, as otherwise the compressor starts cycling, or repeatedly starts and stops. This not only disturbs the power supply systems characteristics, but also the life of the compressor itself! Also practically it is impossible to produce a device that does two opposing functions at a single point, namely cutting off and restarting. Hence a gap is given in the device to function, which is referred to as ‘differential’. Either it is allowed to overcool and restart at the set point or cuts off at the set point but restarts at a slightly higher temperature!
In addition the human body is so sensitive to temperature, that at the same indoor temperature, it feels differently during summer and winter. (i.e) You may feel very comfortable at 22 ˚ C during summer, but during winter a slightly higher temperature will feel more comfortable. The poor combination of your compressor and thermostat do not understand this.
So as long as you have installed an equipments that produces constant cooling irrespective of the load, you have to set your preferred temperature in the thermostat and accept a cyclic nature of indoor temperature and be comfortable with that!
Now enter the new variety of, not only ENERGY EFFICIENT AC units, but also units that can think like you!
How to run AC units efficiently at home or office? PART 3
First you must understand the approximate temperature you feel comfortable at. Then set the temperature to a value equal to or slightly higher than that. Otherwise you suffer like as described above. If you do not know your preferred temperature, find it out. It is simple, but requires a little patience and time. First set the thermostat, say at about 24 ˚ C if there is any marking on the thermostat, or set the pointer of the thermostat to roughly point to 1 ‘O clock position of your clock! Run the unit for a reasonable time, say one day at least. If you feel you require more cooling, then set it at say 23 ˚ C or point it to 2 ‘O clock position (Rotate it to your right). If you feel too cold, then do the opposite. Set it close to 12 ‘O clock position or at 25 ˚ C. After doing such adjustment, again allow the unit to run at least for a day. Then if you still feel not satisfied, repeat the above steps in the direction desired by you. Till you finally feel satisfied.
Now as soon as your temperature is reached in the room, no more cooling is delivered to you as the thermostat would have ordered the compressor to shut off, so you feel comfortable. As soon as the temperature rises above your preferred temperature the compressor again starts because of the command from the thermostat and the process is repeated.
Now there are a few problems with these units. What are they? We will see it in next part.
Now as soon as your temperature is reached in the room, no more cooling is delivered to you as the thermostat would have ordered the compressor to shut off, so you feel comfortable. As soon as the temperature rises above your preferred temperature the compressor again starts because of the command from the thermostat and the process is repeated.
Now there are a few problems with these units. What are they? We will see it in next part.
How to run AC units efficiently at home or office? PART 2
All the AC units are equipped with either reciprocating/rotary/scroll compressors with a thermostat and another button that said, “Off/Fan/Low cool/medium cool/high cool” or similar.
The common misconception amongst many people was that you set the temperature to say, 18˚ C or so, you get good cooling!
It is not so. The rate at which cooling produced has got no relation to the set point temperature of the thermostat.
Unfortunately your AC does not know what you are thinking! The thermostat does its job perfectly and the compressor does its job even more perfectly. How?
Thermostat will keep sensing only the room temperature. If the room temperature is higher than the temperature that you have set, it will simply tell the compressor to keep running. As soon as the set temperature is sensed, with a little bit of safety margin, it will ask the compressor to shut off.
As far as the compressor is concerned, it does not understand the concept of temperature or set point. As long as it gets instruction from the thermostat, ordering it to run, it will keep running. Even if the occupant is freezing to death! That is why many times you would have been compelled to get up and shut off or adjust the unit in the middle of the night. Or if you had a remote, you would have only saved yourself the trouble of getting up. Nothing more than that!
Is there not a better way address the problem? There is. We will see it part 3.
The common misconception amongst many people was that you set the temperature to say, 18˚ C or so, you get good cooling!
It is not so. The rate at which cooling produced has got no relation to the set point temperature of the thermostat.
Unfortunately your AC does not know what you are thinking! The thermostat does its job perfectly and the compressor does its job even more perfectly. How?
Thermostat will keep sensing only the room temperature. If the room temperature is higher than the temperature that you have set, it will simply tell the compressor to keep running. As soon as the set temperature is sensed, with a little bit of safety margin, it will ask the compressor to shut off.
As far as the compressor is concerned, it does not understand the concept of temperature or set point. As long as it gets instruction from the thermostat, ordering it to run, it will keep running. Even if the occupant is freezing to death! That is why many times you would have been compelled to get up and shut off or adjust the unit in the middle of the night. Or if you had a remote, you would have only saved yourself the trouble of getting up. Nothing more than that!
Is there not a better way address the problem? There is. We will see it part 3.
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