Bosch IDS A/C, Humidity, Cycles Per Hour on T-Stat
I know a lot going on in the title
We have 2 new Bosch IDS 2.0 A/C systems (only running as A/C, not heat pumps). On our second summer with them.
Feels quite humid in the house this summer. In reading about Bosch, seems a common complaint for these inverter-type systems. I just changed the dip switch to "expedited cooling" which lowers the target coil temp by 5 degrees and should help with more dehumidification. The CFM airflow was already appropriate.
One thing I was reading was suggesting to lower the cycles per hour to 1. Question is, my Honeywell TStat only has a "Heating Cycles Per Hour" setting and nothing about A/C, or Compressor cycles. Would this mean that the Honeywell uses the same setting as Heating Cycles when using A/C? Right now it was on 5, which is even too high for my heating which should be 3, and I set it to 2.
Is there any problem in doing 2 CPH for a 90% furnace or should I set it back to 3? Also should I look for a newer TStat that has a separate A/C Cycles Per Hour setting?
Comments
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How was the size of the equipment determined? Was a load calculation performed? In my experience humidity issues with Bosch are a result of oversizing based on old existing systems or installation on old undersized ductwork, usually both.
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What model Honeywell thermostat do you have?
An inverter system should be set for 1 cph.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.0 -
Probably with a finger in the air replacement of the 3 ton units I had there before
Definitely a much quieter unit than the old 10 Seer rattlers I had for 20 years prior, but I know these inverters are a different animal
Last night I changed the Dip switch to "accelerated cooling" which is supposed to lower the target coil temp to 37 instead of 42 and therefore improve dehumidification
I wonder if I should buy some newer thermostats that can try to run the fan longer even when the compressor shuts down to further dehumidify? My furnace air handlers are both 2 stage Carrier units so not fully modulating though, so maybe that won't work
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Basement unit is on a Honeywell RCT8101 mounted on first floor living room. This unit does NOT seem to have a setting for Compressor cycles per hour. Only setting is for Heating Cycles per hour. I had it set to 3 heating CPH given high efficiency gas furnace
Attic unit is on a Honeywell TP6320R which is one of those red link units that connects wirelessly to a base unit thats wired to my attic furnace. That Tstat does have a Compressor CPH setting (actually 2 of them, Stage 1 and Stage 2) that I can set between 1 and 9. I would set that to 1.
Should I buy a different thermostat for the downstairs unit that has a specific setting for the cooling CPH do you think?
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Are you measuring humidity? If you're not measuring, you're guessing.
Generally the best dehumidification comes from long run times and low coil temperatures. That means the slowest fan speed that will meet your cooling load.
You don't want to run the fan when the coil isn't cooling. During cooling, condensation forms on the coil and drips into the drip pan and gets drained away. If you run the fan after a cooling cycle, any moisture that's still on the coil will tend to re-evaporate rather than drip off, increasing your humidity.
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"Last night I changed the Dip switch to "accelerated cooling" which is supposed to lower the target coil temp to 37 instead of 42 and therefore improve dehumidification."
A note about that: the efficiency of a heat pump is directly proportional to the temperature difference between the heat source and the heat sink. With air conditioning equipment, everyone wants the highest SEER, and manufacturers can raise the SEER number just by running the coil a little warmer. So of course they do. And the warmer the coil, the less the unit dehumidifies. So then they have to put in an override to lower the coil temperature because otherwise people complain about the humidity.
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I will say that I do feel some difference today after changing to that lower coil temp. Maybe after a few days I will see even more dehumidification.
To answer your other question re whether I am measuring humidity, yes I am just referring to the RH % showing on the little digital thermometer and weather station up in my room. Yesterday it was 62% if I recall. Tonight after the AC has been running for the past couple hours to take the temp down for sleeping (I've got it set to drop from 75 to 71 around sleeping time) the humidity is showing 55% and feeling much more cool and comfortable too
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To the point of slow CFM, I have a question
Is it true that my Bosch is unable to or unlikely to ever freeze up with too low airflow? I had read on forums that the inverters are just seeking a target temp and so would adjust themselves accordingly and thus not freeze.
Right now they're set for around 1025 CFM which I think is right for a 3 ton unit which these Bosch's are set to. I could back it down a little slower if I'm not worried about coil freeze. Balancing that with worry that lower speed may mean warmer temps in some of the upstairs bedrooms that are furthest away from the unit
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You’re not gonna get the humidity below 60% with the thermostat set to 75*. To lower the RH you have to lower the temperature.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.1 -
Okay. On our upstairs it runs down to 71 before bed to cool it down. What I've been doing on the downstairs is temporarily setting it to 71 just to run it for a while and then let it return to 75.
So you're saying just to set it at 71 or 72 or something and let it run?
In a tight house when the outdoor temps get up to 80s then yeah I know what youre saying...it doesn't need to run all day to peg it at 75 and so humidity creeps up over time
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If you haven’t disabled adaptive capacity output (sw4-3) I would do that. It lets the coil temp float up based on some algorithm.
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Ok thanks. I will look that up. It's Off currently (all I did was flip SW4 to ON on each unit). I don't understand what that Adaptive Output is but will Google it.
I turned down the temp to 71 from 75 and so the unit has been running pretty much constantly for several hours now and I am seeing a nice continuous trickle of water coming out of the condensate pipe, so at least I know the thing CAN dehumidify. I think the Sw4-4 probably helped some
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