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| Question about air conditioner regulator implementation |
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| T3sl4co1l:
Well... manufacturers not selling the products they advertise/document is one thing... As for actual operation, it may simply be an offset. For example, my in-wall AC unit has a "economy" mode, which I'm pretty sure just turns off the fan and AC after a while (normal, the fan runs all the time); but to make it worth while, it stays on and off longer, probably drifting to a higher mean setpoint in the process. (I never use that mode, as the normal mode is adequate for the room I use it in.) The concept of representative or related figures comes to mind. For example pipe sizes, which are nominally rated in "inches" in the US, but bear no relation to the actual unit as such. In particular, steel pipe sizes are... bonkers pretty much whatever they are, and copper pipe sizes are mostly nominal plus 1/8" (so '1/2" copper pipe' is 5/8" OD). This... is stupid, but it's accepted industry norm, and everyone working with these materials knows to look up the real dimensions in a table. (And, I forget if metric pipe/tube sizes have the same disparity?) Perhaps your manufacturer is going for a similar thing, where their temperature is calibrated to some value (peak, valley, average, etc.; not to mention temperature drop between sensor and actual system outputs), not to any given parameter you might think / expect. Tim |
| Just_another_Dave:
--- Quote from: soldar on September 17, 2023, 10:27:13 pm --- --- Quote from: Just_another_Dave on September 17, 2023, 09:47:56 pm ---I understand that hysteresis is necessary (I’ve designed on-off controllers before), but what surprises me is that it isn’t centered around the temperature set by the user. For example, if you set a temperature of 27ºC, the minimum and maximum temperatures would be 25ºC and 27ºC (centered around 26ºC) instead of 26ºC and 28ºC. Furnace control panels normally use the second option. According to the user’s manual it is an inverter machine, so it seems that some inverters are on-off machines --- End quote --- It makes no sense that an inverter machine would be only on-off because the inverter would have no use. It just makes no sense. But, of course, inverter machines turn off when they are not needed. Say a machine can modulate between 100% and 30%, then if less than 30% power is required of course it will shut down and start up as needed. And the insistence on a very precise temperature also makes no sense. In any air conditioned room there are not two places with the same exact temperature as the air is moving around. The air temperature is measured at the return entry and nobody is placed there. The numeric indication is merely a reference and will vary all over the room and will vary between units because the sensors will have a deviation of their own. Take several digital thermometers and they will all differ by a degree or two ... or three. The unit may be defective or not but I get the feeling that you are quite despistated regarding all this. --- End quote --- The defect is completely unrelated to temperature control. The reason why I asked about how the control panel is usually implemented is because some of the specifications shown in the repairer’s manual weren’t what I expected. As a consequence, I’m just trying to understand how those systems work. Just for clarification the unit is a SDH 19-050 IDNI from Saunier Duval. Taking into account the previous responses, I understand that the inverter is used for modulating the frequency of the refrigerant plumb. Do those systems use a simple control loop (which measures the temperature error as the difference between the one set by the user and the one measured by the ambient temperature sensor and obtains the required frequency using a constant)? |
| Someone:
--- Quote from: Just_another_Dave on September 21, 2023, 09:01:37 pm ---Taking into account the previous responses, I understand that the inverter is used for modulating the frequency of the refrigerant plumb. Do those systems use a simple control loop (which measures the temperature error as the difference between the one set by the user and the one measured by the ambient temperature sensor and obtains the required frequency using a constant)? --- End quote --- Unlikely any significant smarts or technical complexity to it. Compressors will have a fairly narrow range of efficient operational load/power so even with an inverter modulating the power it will typically only be a 3:1 or 4:1 range. There will be on/off cycling in most installs (even fancy commercial installs don't usually have fully proportional controls). |
| RJSV:
Seems a bit confused, grabbing a possible state of affairs, I.E. that 'there's a defect'. Not aware of sensible accuracy and the whole 'thermal flywheel effect' that can slow things down to where an 'ON-OFF' control cycling is perfectly adequate for usual cooling accuracy. Similar, to use a baby, as example. Hearing that 4 pounds is normal for a 2 month old, you wouldn't totally freak out, if baby was 4 pounds, 1 ounce...would you ? I mean, in cooling situation there are temperatures varying all over the place, but usually not quickly, except for extremes like opening the outside door. Anything controlling to within 3 degrees (f) or so is not bad accuracy. Dissecting 'PID' ? That's not 'control theory',...is it ? A proportional control, on a heat pump maybe, but still doubt that any room-sized volume to be cooled is going to be inside a large variation window, ultimately |
| RJSV:
Oh and also wanted to comment about the setting, '26'...That might not mean '26', degrees, literally as control point but rather as the setting that will CAUSE control to center at '26' on average. That might mean that physically, literally, it might be a switching point of 28, to start the on-off compressor. OR, when the air conditioner is active, might be a switch-off point, at exactly 24.5, for, again, a resultant average, of '26' over the course of the next hour. |
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