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Please excuse my horrible english tongue. It's coming from the eastern side if the Atlantic Ocean. The humidity range accepted as comfortable is between 35% and 60% rh. If the absolute humidity in the supply air is constant the rh value will not change at a constant ambiant T°. In similar cases I regulate the ambiant T to a fixed value (usually 22 °C) and the rh will also be fixed. Does the T° regulation work properly? Is it possible to memorize the ambiant T° values and the heating/cooling valve movements? Is there a unique setpoint for heating/cooling or are used two independant values? First step: Stabilize the T° regulation. Second step: Define the same setpoint for heating/cooling.
The whole problem is summed up here. https://upload.wikimedia.org/wikiped...vel.SI.svg.png
With the heat coil before the cooling coil any heat addition will drive the air further from the dewpoint. Not an optimal setup for humidity control. With variable speed air flow you could affect the sensible heat ratio but I'm sure you don't have that option. https://ideals.illinois.edu/bitstrea...pdf?sequence=2 As Orion said, there may come a point when driving temp down raises relative humidity despite increasing dehumidification. RH Is a ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. In other words the denominator can decrease faster than the numerator without reheat.
Ok cool thanks.
Originally Posted by fisha Ok so here is where I got the idea from, The new Honeywell thermostat Lyric supposedly has some feature that it will self-adjust the temperature based on the relative humidity. I guess they did some research and found that most temperature adjustments made by occupants are driven by comfort levels associated with increases or decreases of humidity. I do this at my house all the time. I am trying to see if anyone has translated this strategy to the DDC world. There are other manufacturers that state they "control dehumidification" and they do just the same thing, they lower the setpoint hoping to remove more humidity. The ones I have seen, state that the room temperature can go as low as 2 to 3 degrees below setpoint. Not much different then someone turning the setpoint up and down manually or using a reset. And in both cases I cant imagine the room temp dropping from 71 to 68 would feel comfortable. From the Focus Pro 8000 manual Adjusting dehumidification settings: residential use This feature can control a dehumidifier or use your air conditioner to reduce humidity. NOTE: If your air conditioner is used to control humidity, the temperature may drop up to 3°F below your temperature setting until humidity reaches the desired level. From a White Rodgers Manual When Comfort option is selected the temperature is altered by the humidity to reflect the true comfort. When Dehum is selected humidity reduction is maximized by continuing to cool below the temperature setpoint Doesnt really sound like some magical formulation or program.
My home unit is not oversized. Nor is the other units I am speaking. Maybe Honeywell is on to something, I will see what else comes out of this.
Fisha, Sizing of Systems are critical so that the Cooling is On for longer periods of time, which will remove the humidity from the air as condensate. Changing Setpoints of the Room Temp up and down are not the solution, because that method will always make the Space uncomfortable before it becomes comfortable, as your Room Temp will swing outside of the allowable max of a 2.0 F range. The reason the System works to dehumidify, is basically because you are causing the Cooling to run or open for the longer period of time needed to dehumidify the Air. Other than Correct Design, the only way to dehumidify is to Reheat the Air, while the Cooling Valve is fully open. One more critical piece of info, is that the Chilled Water Supply must be set at 42.0 deg F. Sounds like your Home unit is sized incorrectly as well. Old Rule; "Engineers are always right" New Rule; "You had better check on their Design, because they no longer perform Lessons Learned on their previous Designs"
Keep in mind there is a huge difference between marketing wank, and the real math behind what its doing. If you lower space temp, you most likely just increase RH. Every mechanical fail cannot be corrected by fancy controls.
Ok so here is where I got the idea from, The new Honeywell thermostat Lyric supposedly has some feature that it will self-adjust the temperature based on the relative humidity. I guess they did some research and found that most temperature adjustments made by occupants are driven by comfort levels associated with increases or decreases of humidity. I do this at my house all the time. I am trying to see if anyone has translated this strategy to the DDC world.
It could be that your system is just not sized properly. The discharge from the unit to maintain space temperature may not be cold enough to provide adequate dehumidification. It sounds like you are trying to fix a mechanical design issue with controls.
I don't think mind readers have been wrapped up in a software module yet. Try the straight line, but I think your chasing the impossible much past that.
Yea they do but I'm looking for something more than a straight linear converter. I don't know if anyone else has considered this, that's what prompted me to post here
I would have thought that Alerton have some sort of 'Reset' block or code. i.e. when input is at level 'a' then output = x when input is at level 'b' then output = y any input between a or b = a proportional output value of x to y
The chilled coil is after the heating coil. Im not really looking for a dehumidification sequence, what I am looking for is a control algorithm that adjust zone temp set point when the space humidity increases or decreases, to anticipate comfort levels.
Is hot water available year round? Is hot water coil after the cooling coil?
The control line is Alerton and the units are fan coils with modulating chilled water, hot water, economizer. I was speaking more generally about this issue since I see this problem with many jobs in the past.
I'm sure many would be able to help here, but what line of controls are you talking about? You need to describe what inputs and outputs you have.
Room Temp/Humidity Control Sequence Does anyone have and is willing to share some logic or a sequence that basically incorporates humidity in a zone and adjusts the room set point depending on the humidity? Basically I have this reoccurring problem where a user constantly adjusts the room set point because of comfort and the issue is not temperature but the changing humidity levels. Thanks.
Room Temp/Humidity Control Sequence
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