I guess everyone is entitled to their opinion. Yours just happens to be grossly incorrect.
First off, relative humidity is relative humidity. It doesn't matter if it's in my living room or in your grow room. The same principles apply when you are trying to reduce it. Stating that the "logic" is off because there is a dehumidifier in the room is extremely incorrect. Please explain to me how it is that his portable dehumidifier is going to remove moisture from his air efficiently when the air the a/c is passing over it's coil is from the room outside? The reason portable a/c units are inefficient in grow room operations many times is because growers are using them incorrectly in tent applications. A/C's are designed to be recirculating heat pumps...this means they are designed to remove heat from the existing air and recirculate that air. In this situation he is constantly cooling one area and then pushing that air into a closed environment in which the air is then heated again. The a/c never has a chance to "catch up". So, by doing it this way of course the a/c will run all the time. You can moderatly make this more efficient by putting a thermometer from the a/c to the tent but I am not sure too many portable a/c units come with thermostat probes.
I too have had my fair share of grow rooms and have built even more. I currently have 8,000 watts in my flower. I have used dehumidifiers in every grow up I have had over 12 years of growing. From tents to 1500 sq.ft. buildings and I have NEVER seen a dehumidifier negate the cooling of an a/c. I just built a grow tent for a good friend who has a journal on this forum with 1000w of lighting and a Co2 generator. He only has a 6500btu a/c and a 70 pint dehumidifier. His tents are in a tool shed that has no cooling and a tin roof. Temperatures where he is are 95 during the day and 80 at night with 85-90% humidity all year round. So if a 70 pint dehumidifier puts out anywhere close to 12,000btu of heating then why is it that his 8'x8' tent can easily be cooled by 6500btu that is only running 50% of the time? How is it that his other tent with 2,000w of lighting can do the exact same? Both of his dehumidifiers run almost 60-70% of the time because of the severe humidity where we are.
You keep talking about the OP's situation like it is one of your rooms. He doesn't have a mini split on the wall or a portable a/c in the room. His a/c is outside of the room. All of this is beside the point. Running a dehumidifier in a room actually makes an air conditioner more efficient. This is common knowledge to anyone who has built a home or worked with HVAC units. Why do you think they build dehumidifiers into a/c's? It's common sense. The less water in the air the easier it is to cool that air. What you are stating is TOTALLY incorrect.
Here is a link to an HVAC forum (
http://hvac-talk.com/vbb/showthread.php?t=174832) with actual professionals discussing the heating produced by an 90 pint dehumidifier (estimated to be 5,500btu) and the beneficial use of an a/c in conjunction with a dehumidifier. I am sorry but your information is incorrect in almost every aspect here. If you experienced problems with a 70 pint dehumidifier and an a/c unit then they were because of something else and not the dehumidifier.
Stating that "any a/c with 5,000btu of cooling" would be able to remove the humididty from 1,000 watts worth of plants is just ignorant. You have no clue what the grow environment is or what the dehumidification needs are. You are using specific instances in which YOU encountered issues as broad solutions to everyone's problems. The climate control issues for anyone's grow varies depending on 100's of factors.
