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Topic: Ducted air improved cooling for very hot weather (Read 985 times) previous topic - next topic

Ducted air improved cooling for very hot weather

We are in Texas for awhile where temps are 100 day, 90 midnight, 80 7-am, so we made some mods to improve comfort with our ducted roof air conditioners.

Removed inside turning vanes in all 8 round ceiling vents so each vent can now flow twice the air volume.  We made 4 round plastic disks to block ceiling vents in areas that we don't need to cool.  During the day the rear is blocked off.  Durning the night the front is blocked off.

We normally run both roof air conditioners to keep our motorhome's front half comfortable during the day.  But the rear roof air is pluged into the bedroom temp sensor to control cycling, which has been a problem when the rear vents are closed off. 

Front air conditioner does not have a separate temp sensor pluged in, so it uses the temp sensor on the thermostat.

We found that if we unplug the bedroom temp sensor, the rear roof air will cycle on the front thermostat, which is exactly what we want during the day.  Each roof air unit has a 2-wire white plug above the foam filter that can connect to a separate temp sensor (thermistor).

At night we close our ducted ceiling two retangular forward facing air vents, cover front round vents, plug the bedroom temp sensor back in (needs to be on a switch) and run just the rear roof air.

Re: Ducted air improved cooling for very hot weather

Reply #1 –
In Arlington TX, we have had no-rain, 103 degree days, 80 degree nights for last few weeks and the same is forecast for the next few weeks.  With a few changes, our two original roof air conditioners continue to cool down our interior just fine.

We have two common ceiling air ducts running fore & aft, for both front & rear roof air conditioners with eight ceiling vents, four in bath & bedroom and four in front living area.  Normally the front unit uses a front temp-sensor for control and the rear unit has its own temp-sensor located in the bedroom. 

I have a simple way to change the rear air conditioner to temporarily use the front temp-sensor.  We also made covers to close off the four rear ceiling vents during the day.  Both units run pretty much not-stop during day, but they have no problem keeping just the front cool.

During the night, we put the rear AC unit back on the bedroom temp-sensor, close off the front four vents and we sleep at 72 degrees with just the rear AC cycling on & off.  We are using about 50 Kwh of electricity each day.

Re: Ducted air improved cooling for very hot weather

Reply #2 –
That's pretty slick Barry.  In less severe conditions where 1 AC is sufficient I would like to do the following:
    • During the day:  Use the rear AC but controlled by the front temp sensor.
    • For sleeping:  Use the forward AC controlled by the aft temp sensor.
My reason:  I hate noise.  This approach would put the noise at the other end of the coach.

It sounds like your approach of unplugging (with a switch) would nicely address the day-time issue.

Audrey & Harvey Nelson
2000 U-320, 40' towing 2014 Jeep Grand Cherokee
nelsonah@ieee.org

Re: Ducted air improved cooling for very hot weather

Reply #3 –
Barry, Also enjoyed your info on a/c and the energy used. 
I am guessing each a/c draws about 14 amp run load indicating for both you are using
about 3.3 kw per hour.
Now I wonder if you are getting any advantage from all the solar cells on roof to get your total load down to 2.08 kw per hour from the meter ? 
Maybe the a/c units draw little less than 14 amp ?
I just get into somethings.
Thanks

Re: Ducted air improved cooling for very hot weather

Reply #4 –
I'm looking for a 4 button Dometic control for my front A/C heat pump. If anyone has one that they have replaced with a 5 button and want to get rid of it please PM me.
Rick

Re: Ducted air improved cooling for very hot weather

Reply #5 –
Harvey,
Quote
For sleeping:  Use the forward AC controlled by the aft temp sensor.My reason:  I hate noise.  This approach would put the noise at the other end of the coach.

I just put a double-pole double-throw center-off switch hanging out the side of the rear roof air to disconnect our bedroom temp-sensor from rear unit.
We could run a pair of wires from rear roof air to front roof air through the common ceiling duct to easily bring your quiet sleeping creation to life.  One scenario is:

SWITCH-POSITION          FRONT-AIR-CONDITIONER          REAR-AIR-CONDITIONER
      center-off                    normal: front temp sensor          special: front temp sensor
          rear                        normal: front temp sensor            normal: rear temp sensor
        front                        special: rear temp sensor            special: front temp sensor   

Another scenario would be to have an option to run both roof airs on rear temp sensor.
Dave,
Quote
RE:  I wonder if you are getting any advantage from all the solar cells on roof to get your total load down to 2.08 kw per hour from the meter

We have been plugged into 50-amp for the last month, so both roof airs are the main draw on the electric meter.

Since our solar project is complete we are seeing a few amps from solar panels powering our 12-volt needs.  Without solar our battery charger would be covering these small 12-volt loads and our electric meter would be a little higher.  But several times during the day, I have turned off the main-panel breaker to the battery-charger and we have seen about 30 solar amps powering our inverter.  But roof air conditioners still ran on shore power.