Central Air Conditioner Control

[cadillackid]

I use an algorithm with cooling that runs the A/C more at night when its cool outside and also in the mornings and then less when its at the peak heat outside.. saving energy because of lower head pressures and more heat transfer from the condensor...

example: target temp is 74 at night 76 occupied day, 78 unoccupied.. so in the early AM when everyone leaves the house the A/C cools down to 73.. then at 10am(or if outside temp goes up quickly) the setpoint is raised to 74.. then raised at 11am to 75, noon to 76, 1 pm to 78.. notice the trend.. the A/C is allowed to warm up a little each hour so that the system runs less and less as it gets warmer outside... by the time occupants arrive at 7 or so pm its begun to cool off outside and so dropping from 78 to evening 76 is easily handled.. then after sunset for bedtime the system drops to 74.. so most of the heavy cooling is done when the sun is down...

although I surely dont understand the idea of saving energy to the point of changing comfort level like the above post.. i want my system to run and keep me comfortable.. not wearing 6 layers of sweaters or having to wear shorts to stay cool...
-Christopher

[Steve Q]

Excellent information!

This is exactly the kind of discussion I was hoping to generate. Lots of great ideas here.

I have a older house so I am limited on what I can do with zone control and air intakes. But, I am thinking about some remodeling: maybe I can make changes to my HVAC system.

I really like the idea of changing the AC setpoint as the outside temperature increases. This would be a big energy saver for me, because my AC is slightly undersized and runs 100% of the time when the outside temperature is 90+ degrees.

Keep the ideas comming!

Steve Q

[completelyhis]

would anyone be willing to share script samples of how the adjust the setpoint in relation to the outside temp?

[Steve Q]

would anyone be willing to share script samples of how the adjust the setpoint in relation to the outside temp?

I think this could be easily done with a conditional event such as: if outside temperature > 85 then change thermostat set point to 78. 3 or 4 such events could probably cover the range of 85 to 95 degrees. However, this approach requires a programmable thermostat.

Or a simple script could set the thermostat to "outside temperature - 7" Again however a programmable thermostat would be needed.

In my case, I do not have a programmable Tstat, so I would set my thermostat to a fixed comfort point of 76 degrees. When the outside temperature reached 85, I would turn off the AC (for at least 15-20 minutes) then turn it back On again when the inside temperature reached 78 degrees. Then OFF again at 77 degrees etc.

This approach would allow your Tstat to be in control when the outside temp is 85 or less, but puts Homeseer in control when the temp gets above 85.

What do you think? I will write a script for my application and I can send it to you.

Steve Q


Steve Q

[psampson]

although I surely dont understand the idea of saving energy to the point of changing comfort level like the above post.. i want my system to run and keep me comfortable.. not wearing 6 layers of sweaters or having to wear shorts to stay cool...
-Christopher

Hi Cadillack Kid and Steve Q,

We don't really change clothes, nor is comfort affected. (although depending on how green you feel you might save more trees by taking clothing into the equation) However, the run on-time of the plant is another indicator of the differential of inside .vs. outside temp when you are using a heatpump and also the energy consumption of the plant. (cent-a-meter can augment energy consumption measure of plant)

If the pump does not reach the specified setpoint in a time period (this is my main variable I have been playing with on and off periods) and the outside/inside differential remains constant (or decreasing) then you can ride the setpoint right around that temp for a degree celcius or so and still save some energy. Your system is not going to get where you originally set anyway. I also neglected to say I have external temp/humidity sensors which I can test inside against.

Using on and off run-time as an adjunct to major rules I find a useful way of being more dynamic than picking times of day for various setpoints and ranges alone. I changed to the run-time differential method just this past year, and just completed my first full year with it. Jury is out, but my bill IS less.

Ideally, especially for extreme differential or undersized systems that run forever, the runtime dynamic method in combination with some scheduled setpoints is most interesting to me. The idea being setpoints can be set at certain times as you have, based on external temp or occupancy, and dynamic methods used around those points, my current testing being addition of run-time.

While I don't use your method and might try it to be a bit more granular, my setpoints to specific "starting" temps are the 9am reset to prefered seasonal temp and the disarming of the alarm indicating occupancy setting the same. Armed house sets the improbable setpoint for the season and guarentees the plant does not run if no-one is home, might not work for some global areas seasons who need consistant temp, but helps my poor memory for turning things off.

Graphs of my method also indicate that my method quickly impacts humidity inside to improve the comfort level without the need to change the thermal momentum of all the walls and house fittings via heatpump air circulation only which takes MUCH longer. Sometimes this is enough in my climate. So I am thinking of trying a dynamic method triggered by room humidity (have wireless Oregon sensors there) or a combination of temp/humidity for some peak humidity seasons - in essence humidity differential also.

Other graphs show that my plant draws about 30Amps*240V when cooling and 38Amps*240v when heating, so somewhat assymetrical for some reason. For my energy cost its about $1 per hour. If it were to run continuously, that would be 70-80 tonnes of greenhouse gasses per year (according to my power utility and cent-a-meter/HS) Singly the biggest consumer in my house so a prime target to increase on-time efficiency if I can.

I do wish my house had much better insulation in the walls. So a lot of heat/cool is lost in house designs where I live and it is common for plants to run on forever. So heating a room and expecting it to stay heated for a reasonable time in winter peak rarely works and the opposite in summer peak.

My plant is quite old and not efficient like the inverter pumps, nor does it have the 24v standard interface common for electronic thermostats. In fact, my system has several Honeywell older bi-metal thermostats which seem to have very large hysteresis and it's not adjustable often making me feel it should be on when it's not, or it should shut off when it doesn't - so I used to ride them a lot by hand. So just taking those out of the equation and having finer grain control seems to reduce the variation of internal temp to below my level of conciousness. It's all 240V controls so I am limited, but pleased with what I have acheived so far and it's a good BBQ talking point

Additionally, I did once find a virtual HS thermostat device on a european home automation site which implemented a heat pump thermostat in HS thermostat script and HS recognized it as a thermostat device and the back end turned on/off HS devices for compressor and fan control. A soft HS thermostat. I tried to modify it to my needs but the comments were not english and gave up in the end. If someone uses this it would be great if you could share!

I have attached an example graph for the past week of some of the things I compare using (the excellent plugin) powertrigger graphing - int/ext temp and humidity, upstairs downstairs and house overall power summed from the three phases- big spikes are HP plant=on. The low energy first part of the week was nice (I was away on business).

Of course my 6amp steady state consumption needs some work too..

A very interesting thread. Thanks all.

cheers,

Phil

[psampson]

Oops, forgot to mention for those looking at the graph in my previous post.. It is Winter in Australia this time of year! So I am heating.

cheers,

Phil

[wigalo]

OK guys, I'm new to this form and this is exactly what I'm looking for...I posted on Cocoontech several months ago, but no one seemed interested.

I think HS may be the link I need to get the funcionality that I want. I'll copy and paste my 2 posts from CTech. Please excuse, because it will be a long read...

I'd like for all to chime in on if what I want to do is doable (sounds like it is based on what I've read in this post) and if someone has written a similar script.


1st post...

We are months away from breaking ground on a custom construction home. One of the things that I'm determined to get right is the HVAC. In particular, I want each major area to be controlled on it's own zone. The house will be 2 stories with about 7300 sq ft of living area. Based on the layout of the home, I'm thinking that we'll need 9 independently controlled zones.(1 unit upstairs, 1 for downstairs)

I've selected Omni Pro II as the Automation board ( have the Aegis 2000 in our current house, it's bullet proof, I'm familiar with the programming and the Omni is basically the same unit) Currently I have my Aegis set up to manage the communicating T stats. (ie set back at night, when alarm "armed", etc) What I'm looking for though is True automation of the zones.

I ran across this post on the site, but the member hasn't logged on since early december....

[i]HVAC
COMPLETE HVAC CONTROL. Luckily, we started this project in the building phase. Because of this we were able to install motorized dampers into the HVAC system. The home has a single furnace on each floor, each floor has 3 zones. A total of 9 zones and 9 thermos. This has been absolutely amazing to watch. The software has been loaded to monitor living conditions and trends. It's been amazing watching how precise it has kept the different temperature in each zone and "learning" the best way to utilize the system.
*Very Basic Example" -- During the winter it has learned that it is much more effective to generally use the lower level furnace and let the heat rise to the higher floors. The entire house has stayed within 9/10 of 1 degree in all zones 97% of the time. The local gas and electric company actually knocked on the door and asked "curious" questions as to the low utility usage of this home opposed to the others in the neighborhood. I can't tell you how ecstatics my inner geek was this point.[/i]

This type of automation of the HVAC is exactly what I'm looking for.

Does anyone know what software he may have loaded? If a variable speed blower is present...is the zoning program smart enough to make sure that if only 1 or 2 zones are calling for heat/cool, the excess air is either being "dumped" into another zone, or ramping the fan speed down? Is there an interface that I would use instead of the traditional zone controller, or do they make a zone controller that interfaces with HA?

Just to give you a bit more of what I'm going for, check this site out...

www.homecomfortzones.com

All the zone boards that I've found only allow control of the communicating t stats(change temp, fan status via automation) but no logical input from sensors/conditions of HA or monitoring of living conditions or trends. I would basically like to do all that JClarke's or Homecomfort's system (ie use active mixing of air between too hot and too cool zones before system calls for heat or air, monitor static pressure in plenum and ramp variable speed fan up or down depending on number of zones calling for conditioning) but automated.

What do you guys think, is this possible??

2nd Post

Ok, so since no one else has anything to offer, I'm going to write my own "Automated HVAC" script. It'll be at least a year before it's up and running, but I will start working on it now, so that hopefully it's perfected by move in day.

I got a prelim bid from my HVAC guy. We are going to go with Geo thermal, and he'll be installing a 5 ton Climate Master Tranquility Series water to air variable speed unit to take care of the downstairs load and 4 ton unit to service the 2nd floor.


What I want to accomplish:

1. Reduce overconditioning. Eventhough my current home has 2 zones (upstairs/down), the master is still always warmer than the rest of the upstairs...to get it comfortable, the kids' room and everywhere else upstairs for that matter is too cold.

2. Reduce conditioning of unused rooms...If guest bedroom is unoccupied, I don't want to pay to condition it.

3. Use automation panel for set back i.e. when alarm away and winter flag on then set temp 65 degrees.

4. Smart Circulation. I would like to be able to balance temps between rooms by mixing and circulating air w/out calling for heat or cooling when possible.

Here's where you all come in...I'll jot down some ideas of how I will accomplish the above, and look forward to you sharing your expertise on how to improve on my ideas.

EQUIPMENT
I had a Manual J done, so I know the exact CFM requirements for each zone. I will have him run the supply duct as well as a return for every zone to optimize the "air mixing effect" to minimize the need for conditioned air. In addition to dampers being placed on the supply duct for each zone, they will also be placed on the return duct.

I will have communicating T Stats in the "Master Zones" with Temp Sensors in the "Slave Zones".
Temp probes in all return registers and in the Plenum
Electronic Barometric Relief bypass damper (to compensate if only 1 or 2 zones are calling for condtioned air)
occupancy sensors

EXECUTION:

MIX: If zone (Kid room, Zone "K") calls for heat AND any other zone (A for example) is above setpoint THEN Open "Zone K" supply and return damper; Open return Damper zone (A) AND if Plenum temp is less than zone (A) then open supply damper and if fan is off then fan on.

My hope is that this will effectively use mixing of current air to bring rooms to desired comfort level. If the rest of the home doesn't need conditioned air, the fan is much less of an energy consumer than the furnace or a/c.

Also, eventhough I plan on having 9 "zones", I will have 4 master zones that will control hvac equipment and 5 slave zones that will operate supply/rtn dampers and adjust master zone tstat if the slave zone actually needs conditioned air accordingly.


Finally, this logic would be difficult at best with the Omni, will HS make it easier?