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What is the most energy efficient heating or cooling schedule?

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    What is the most energy efficient heating or cooling schedule?

    I searched around but i am not finding much results. I am also not very familiar with hvac or thermostats. But basically i am looking for what the most efficient schedule for heating and air would be to setup in homeseer. For example, is it more efficient to turn the air off when i am not at home and let it get really hot then try to cool it down before i get home, or more efficient just to raise the temp a little bit higher, and if so by how much. Just curious what everyone else has found to be the most energy efficient way to schedule their hvac. thanks!

    #2
    I just use "occupancy" to set the thermostats back a couple of degrees. Then, when "Occupied" it goes back to a preset value. I had intended to build a history and come up with an algorithm, but never could figure out how to attack it.
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      #3
      cooling is most efficient when your A/C unit is not in the sun.. and ultimately when it is coolest outside...

      if you work a regular daytime work schedule, and say you want a target temperature of 74 for when you are home.. if your A/C unit is in the sun in the morning, then a schedule to raise the temperature through the morning and then slowly begin to drop it in the afternoon.. paying attention to the fact the hottest part of the day in summer occurs about 4-5 PM.. so runnin g lots of A/C then will make it work harder and pull more current...

      I let homeseer determine how far back my set-back will be based on outside temp forecasts, sun-load and also actual outside temp...

      so I get up in the AM and my house is 67.. my target daytime temp when I get home at 5 is 75.. my A/C units are in the sun in the morning on hot sunny days.. my system sets back to 72 and allows the units to run at 72 until it sees the sun hitting them.. the sun is strongest through noon.. so they dont run at all.. at noon or thereabouts it resets them on to 80. it leaves them there till 2pm when it goes down 1 degree per hour till they reach 75...

      My units are inverter variable speed units so they will most likely run continuous whe ncalled for.. so thats why the slow drop in temperature. so they stay in low speed (most efficient)....and I have best results with that scenerio...
      -Christopher
      PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

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        #4
        Great info Christopher. Thank you for the insight. Do you have a sensor that detects sunlight on the outdoor unit(s), or do you calculate that based on forecast and time of day?
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          #5
          Originally posted by reidfo View Post
          Great info Christopher. Thank you for the insight. Do you have a sensor that detects sunlight on the outdoor unit(s), or do you calculate that based on forecast and time of day?
          Yes how do you detect that?
          Hector
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            #6
            I do several things to detect sunload...

            1] I have 4 sensors on my house itself, 1 on each side.. so when there is a large differential I know that the sun is out... I purposely did not pagoda my outside temp sensors for this purpose..

            2] each of my units has 2 sensors that I use..(among many) a center coil temp and also an ambient air sensor.. I read those to get an idea of how hard the unit is working, and the air temp being brought into the condensor.. if the sun hits the back of the house I will see first the coil temp rise (on a non operating unit).. and the ambient air temp rise...

            3] I can also approximate how hard the units are working by monitoring the superheat and subcool across both coils.. I do this anyway as its an early indication of a freon leak if one should occur.. before i lose performance (or the whole charge)...

            -Christopher
            PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

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              #7
              Originally posted by cadillackid View Post

              3] I can also approximate how hard the units are working by monitoring the superheat and subcool across both coils.. I do this anyway as its an early indication of a freon leak if one should occur.. before i lose performance (or the whole charge)...
              Christopher,
              You have more info on how you are doing this?

              Thanks,
              Ken J.

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                #8
                superheat and subcool is nothing more than the temperature differential from refrigerant input to output of a coil...

                sub-cooling is on the condenser side, superheat is on the evaporator side..

                in the industry, there are charts to follow for this based on the humidity, ambient temperatures, and CFM of airflow across a coil...

                since I know all of the variables.. and have sensors at the beginning, middle, and end of each coil I can calculate what the value should be vs what it actually is....

                in a low charge situation, refrigerant on the evaporator will evaporate too quickly causing the first portion of the coil to be colder than the rest... basically the refrigerant is all evaporated and in a gaseous state before even reaching say halfway across the coil...this will show up that the coil input to output temperature difference is much higher than it should be.. you as a consumer may still have nice cold air from the vents.. as a system continues to lose refrigerant it will cool fine in low humidity but not as well in high humidity, and may freeze up into ice...

                refrigerant is expensive.. if a low charge is detected early, and a leak found, the existing refrigerant can be sucked out, saved, and re-used in a system after repair...

                most often the first time a service call is made to an A/C system because the consumer says.. man this thing just doesnt seem as cold... a system may have lost 30-40% of its refrigerant charge...

                when i used to work on large commercial systems that held 120 lbs of freon... thats a lot of money to be saved by early malfunction monitoring..
                -Christopher
                PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

                Comment


                  #9
                  Christopher, did you ever solidify your board design (interface to your MS's)? I read a thread on one of the HVAC forums where you were in the process of working out the details/kinks. Seems it was in 2009 'ish. I'm in the process of tightening my house and thinking of ways to deal with the ductwork in my attic. We hit temps of the low 100's a couple of days this past week and our upstairs unit was struggling to keep temps down below 80. Which brings me to another point...

                  Along the lines of working out an algorithm to determine the best runtimes vs. comfort... I'm going to come up with a formula/system to anticipate outdoor temp loads vs runtimes to balance comfort. We already set back the t-stats via homeseer when the house is in "Away" mode. Now that I have some data logged for system performance (degrees cooled/time during varying conditions), I should be able to come up with an anticipation algorithm that will get me close. The key is having some historical data of varying conditions vs. cooling times.

                  Frank

                  Originally posted by cadillackid View Post
                  superheat and subcool is nothing more than the temperature differential from refrigerant input to output of a coil...

                  sub-cooling is on the condenser side, superheat is on the evaporator side..

                  in the industry, there are charts to follow for this based on the humidity, ambient temperatures, and CFM of airflow across a coil...

                  since I know all of the variables.. and have sensors at the beginning, middle, and end of each coil I can calculate what the value should be vs what it actually is....

                  in a low charge situation, refrigerant on the evaporator will evaporate too quickly causing the first portion of the coil to be colder than the rest... basically the refrigerant is all evaporated and in a gaseous state before even reaching say halfway across the coil...this will show up that the coil input to output temperature difference is much higher than it should be.. you as a consumer may still have nice cold air from the vents.. as a system continues to lose refrigerant it will cool fine in low humidity but not as well in high humidity, and may freeze up into ice...

                  refrigerant is expensive.. if a low charge is detected early, and a leak found, the existing refrigerant can be sucked out, saved, and re-used in a system after repair...

                  most often the first time a service call is made to an A/C system because the consumer says.. man this thing just doesnt seem as cold... a system may have lost 30-40% of its refrigerant charge...

                  when i used to work on large commercial systems that held 120 lbs of freon... thats a lot of money to be saved by early malfunction monitoring..
                  -Christopher

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                    #10
                    I did indeed get my MiniSPlit boards working.. Ive been running the system for 3 years now.. this week was the first time I ever saw it actually work hard.. for a time it had to run flat out to keep the house at 68.. well ran flat out for just a couple hours.. the compressors and outdoor fans that is.. but with the actual ambient at 103, and dewpoint at 70.. with full sun (no clouds, no breeze) i feel that it passed the test.. its not uncommon for me to reach 100% indoor blower when trying to do a cool-down.. (yes im dumb.. I open all the windows cause I love summer air.. then i roast so I close up and want quick cooldowns (which i get))... though during the heatwave I had the windows closed for several days.. which usually only occurs in winter at my house...(windows closed for days at a time)...

                    of course my Minisplits arent Minisplits anymore.. I modified them to the point I use their coils and electronics but built my own enclosures and mounted them into my ducted system with dampers and a central blower.. it works very well as the units follow my lead on holding coil temps at efficient levels based on the amount of air I feed over them.. (they maintain constant temps)... as they gert closer to setpoint I lower the amount of air over their coils.. all the while feeding the units a "fake" thermistor value so they also know they are nearing setpoint and back off the compressor and allow coil temperatures to relax.. its a win-win. once its compressor shuts off, I close the damper to that zone, thus that unit is off and satisfied...

                    what i get is rarely a time they run flat out but when I need lots of heat or cool they can and do provide it..
                    -Christopher
                    PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

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