HVAC Monitoring System - Buy?Make?

With electricity costs getting more expensive, and a hot as ^%$&^%$ summer, I am wondering why I haven't found a good clean way of monitoring my HVAC system performance to make sure it is running at it's optimal efficiency.

I would think we would need:
evaporator and compressor line pressures
evaporator and compressor line temps

House:
Inlet Air temp
Outlet Air temp

Outside Air temp and humidity

And a digital psychrometric table/chart and software to read inputs and the psych chart.

I and others have spent hundreds of dollars on other neat automation toys, but why not one like this? This one has the potential to have a large return payoff (running your AC just one summer at sub-optimal condition can really up your monthly costs) and you might not really notice it because AC performance degrades slowly (just like a small refridergant leak).

Ideas????

I was also thinking about this just a couple of weeks ago as stupid Nevada Power here raised their rates and now my power bill has officially gone over the "panic" (for me anyway) price of $400 a month!!!

I would think power monitoring to the compressor with a current donut and temperatures would be interesting to plot as that is easy to do. The pressure lines would take some doing and I'm thinking a problem with your unit might show up with the other readings (once your system is tuned and you know what an optimal level of cooling is).

There are some consumer based energy monitors that would work out well for the current monitoring if you didn't want to go custom donut/analog to digital converter and they even have some nice graphs and power/cost calculators built in as well.

I live in a very low humidity environment (Las Vegas) and am thinking about taking advantage of using a 'pre-cooler' to lower the air temperature of the surrounding compressor so it did not have to work as hard providing cooling to the system (a lower temp differential would result in a lower running compressor pressure and greatly reduced current). What would be cool is to measure the ambient temp, then the temp right at the coils to see the pre-cooling result and it's affect on the compressor's current.

I actually built a home made pre-cooler in my younger days at my first house and remember it reducing the current to the compressor (I did a quick test with a clamp on current meter). I just built a wood frame around the round compressor (located at ground level at this house), put swamp cooler pads around it, lined the top with sprinkler pipe (PVC), drilled small holes on the side of the PVC, then used paint nozzles to direct the holes downward to soak the swamp cooler pads. I then connected this to my sprinkler system via a 1/8" tuning valve (min water for max cooling) and had the compressor's relay 24 vac trip a sprinkler valve (as the solenoid to this valve was a common 24 vac as well) so the water would only turn on while the compressor was running.

Anyway, just some quick thoughts.

BraveSirRobbin said:

I was also thinking about this just a couple of weeks ago as stupid Nevada Power here raised their rates and now my power bill has officially gone over the "panic" (for me anyway) price of $400 a month!!!

I would think power monitoring to the compressor with a current donut and temperatures would be interesting to plot as that is easy to do. The pressure lines would take some doing and I'm thinking a problem with your unit might show up with the other readings (once your system is tuned and you know what an optimal level of cooling is).

There are some consumer based energy monitors that would work out well for the current monitoring if you didn't want to go custom donut/analog to digital converter and they even have some nice graphs and power/cost calculators built in as well.

I live in a very low humidity environment (Las Vegas) and am thinking about taking advantage of using a 'pre-cooler' to lower the air temperature of the surrounding compressor so it did not have to work as hard providing cooling to the system (a lower temp differential would result in a lower running compressor pressure and greatly reduced current). What would be cool is to measure the ambient temp, then the temp right at the coils to see the pre-cooling result and it's affect on the compressor's current.

I actually built a home made pre-cooler in my younger days at my first house and remember it reducing the current to the compressor (I did a quick test with a clamp on current meter). I just built a wood frame around the round compressor (located at ground level at this house), put swamp cooler pads around it, lined the top with sprinkler pipe (PVC), drilled small holes on the side of the PVC, then used paint nozzles to direct the holes downward to soak the swamp cooler pads. I then connected this to my sprinkler system via a 1/8" tuning valve (min water for max cooling) and had the compressor's relay 24 vac trip a sprinkler valve (as the solenoid to this valve was a common 24 vac as well) so the water would only turn on while the compressor was running.

Anyway, just some quick thoughts.

Click to expand...

Thank you for posting this idea about the precooler. My humidity runs from 30% to 40% and I may still try it.

It would not be terribly hard to monitor your evaporator temp, condensor temp, current draw, and static air pressures. A cai webcontrol could handle all of that using one wire sensors for temp and pressure transducers at different stages of your air handler. A doughnut as mentioned fur compressor current draw which outputs an analog signal would also be readable by the cai. The cai has three analog inputs, 8 digital inputs, 8 temp inputs, and 1 humidity. Pressure transducers made by freescale and found on digikey.com will do the job and cost about $10 each. One wire temp sensors can be had from digikey as well (or ebay).

So, three analog inputs could measure static pressure in the return plenum, pressure in the main trunk, and current draw. Temp sensors could be placed on the evaporator, condensor, outside air, inside air, and main trunk?

Monitoring your freon pressures requires someone with a license. You would need to evacuate the system, cut into the copper, solder (high temp silver solder) in a pressure transducer, and recharge the system. Perhaps your system already has pressure transducers for freon that you could be piggy back off of?

My carrier infinity system actually monitors most of that and it can be read from the thermostats. They have a network interface for it that probably could be polled allowing storage of the data for graphing purposes. The cai for sure can be polled. You would need to be able to write some software and have a pc running that gets/stores the data points.

Curious how we talk about compressors drawing less current when the pressure goes down. This is the opposite of what we were talking about with water pumps. It must all come down to the controllers. I have also noticed that my table saw draws more current when it has a load.

Lou, please don't take my explanation verbatim as I'm NOT a professional (I only play one on CocoonTech) AC person! I just know from direct experience that when you pre-cool the air entering the compressor you can actually see the current draw go down (I do have first hand experience with this as mentioned above).

Sorry I can't give a more detailed technical reason. :blush:

Charles, with your humidity that high I am really doubting a water based pre-cooler would work out for you. Maybe do some more investigations on swamp cooler maximum humidity operating efficiencies and scenarios.

BraveSirRobbin said:

Lou, please don't take my explanation verbatim as I'm NOT a professional (I only play one on CocoonTech) AC person! I just know from direct experience that when you pre-cool the air entering the compressor you can actually see the current draw go down (I do have first hand experience with this as mentioned above).

Sorry I can't give a more detailed technical reason. :blush:

Charles, with your humidity that high I am really doubting a water based pre-cooler would work out for you. Maybe do some more investigations on swamp cooler maximum humidity operating efficiencies and scenarios.

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I hope you didn't take my comment in an argumentative way. I didn't mean that. I just find it curious how different electric motors behave differntly.

I believe you when you say the compressor draws less current when it isn't pushing against as much pressure. I really don't understand the electronics of motors because when you stress some types of motor with higher resistance, the motor slows down and draws less current. Others, the motor draws more current and either slows down or stays the same. My table saw slows down and draws more current. The rpms slow down, you can see that with your naked eye. I have never put an amp meter on my table saw, but I don't know how else you get lights dimming and circuit breakers popping if it isn't because more current is being drawn. If I bring the blade to a stop, the breaker always pops, if I slow it down for long enough (several seconds) the breaker will pop also. With typical (proper) load or no load the breaker never pops.

And yes, I know that I shouldn't be loading my saw blade like that, but sometimes when you try to cut a large sheet of plywood by yourself it's hard not to bind it up. :angry:

Yea, I was just trying to say that i really didn't know the technical reason the current reduces (hopefully someone here can state the reason) but I believe that is has to do with the pressure the compressor motor has to work 'against' (I guess you could call this 'resistance'). The larger the temp differential, the higher the pressure (and current) maybe?

Back to the OP, For about $100 you could get a cai, several temp sensors and several pressure transducers and monitor pretty much everything except freon pressures. I don't know how to get amps into an analog signal in the 0 to 10v range (as accepted by cai). Maybe someone else does, but I bet if you know what to look for, digikey probably sells it.

I recently experienced a similar issue (a leak) which caused my AC unit to run pretty much constantly. The temperature reading at the primary air outlet was 60 degrees. The AC guy put in .75 lbs of Puron and then the temperature at the primary air outlet dropped to 45 degrees! I am adding a temperature sensor to the primary air outlet and inlet so I can compare those readings with the outside temperature/humidity. For my need, I really don't care what the evaporator and compressor line pressures are. What is important are the readings between the air outlet, inlet and outside temperature. I now need to come up with the formula to determine when the air temperature at the primary outlet is not within range.

I am using HomeSeer, Ultra1Wire2 HSPI, EDS OW-SERVER 1-Wire to Ethernet Server and several 1-wire temperature sensors.

Regards,
Ultrajones

BraveSirRobbin said:

I live in a very low humidity environment (Las Vegas) and am thinking about taking advantage of using a 'pre-cooler' to lower the air temperature of the surrounding compressor so it did not have to work as hard providing cooling to the system (a lower temp differential would result in a lower running compressor pressure and greatly reduced current). What would be cool is to measure the ambient temp, then the temp right at the coils to see the pre-cooling result and it's affect on the compressor's current.

Click to expand...

I would be careful with that pre-cooler. I had one a couple of years ago and the flap ended up staying up so it would run all the time and one of the misters popped off. It ended up costing more in water than it saved me in electricity.

Jimmyjam said:

I would be careful with that pre-cooler. I had one a couple of years ago and the flap ended up staying up so it would run all the time and one of the misters popped off. It ended up costing more in water than it saved me in electricity.

Click to expand...

Wow, that's good to know. I was wondering about the quality/durability of that item. I just may build one myself as you can get those misting heads (used to cool down patio areas) and couple it with a sprinkler valve that will be controlled via the 24 VAC of the compressor's control relay coil. Plus the darn thing is $100 and I would hate to pay that and be disappointed on its quality.

Another thing I was wondering about is how the compressor would hold up with water being sprayed on its coils all the time. As was pointed out to me on the chat, it IS meant to be out in the rain, so I guess "near continual" rain should not damage it at all!?! :unsure:

BraveSirRobbin said:

Another thing I was wondering about is how the compressor would hold up with water being sprayed on its coils all the time. As was pointed out to me on the chat, it IS meant to be out in the rain, so I guess "near continual" rain should not damage it at all!?! :unsure:

Click to expand...

Its the condenser you're spraying water on, not the compressor. Although the compressor is usually inside the condenser so its a moot point.

I've heard that depending on your tap water quality, minerals in the water will build up and eventually clog the fins.

ultrajones said:

What is important are the readings between the air outlet, inlet and outside temperature. I now need to come up with the formula to determine when the air temperature at the primary outlet is not within range.

Click to expand...

When the A/C is running, you should have a Delta-T of 15*-20* F. Measure the temp before the evap coil (return air) and subtract the temp after the evap coil (cooled air).

Take the temps at the evap coil itself, not at the return(s) and supply vents. The air inside the ducts can pick up heat along the way and skew the results.

Measuring additional temps at the return(s) and supply vents can help you determine if and where the supply air is gaining heat in the duct work.

The A/C is a closed system so the outside air temp doesn't factor in to its Delta-T efficiency.

If your A/C is cooling properly at the evap coil and your house still isn't cool, then you need to look elsewhere (sizing, ductwork, insulation, and/or attic venting) for why. My guess is that a majority of homes have HVAC/insulation problems due to builder shortcuts and, more typically than not, sloppy work.

Just a note relating to a commercial endeavor I was involved in; mostly relating to tweaking an AC unit for best efficiency. The price tag at the time for then endeavor was around 250K so I kind of documented each piece of it.

I am not sure what the tool was; but there was a device utilized to measure the air flow at the main supply duct. A small hole was drilled into the main duct. Two instruments were used; a flow sensor and a temperature sensor. The temperature sensor was digital and the flow sensor was analogue.

Somewhere there were documented specfications relating to the optimal supply and return air flow and temperatures for peak efficiency (sq footage of supply and return ducting type stuff).

In addition a small ducted instrument was used to measure air pressure at the supply ducts such that each one could be adjusted for optimal flow.

This was also in addition to monitoring the compressor line pressures. There was also an adjustment on the main blower motor (never seen this before) such that you could adjust the motor such that it would provided the most efficiency using amperage draw specifications / RPM and the ability to tweak it for most AMP/RPM's.

As mentioned earlier; a house system is closed and aside from just measuring temperatures and the ability to utilize HA adds more options relating to measurements and optimization. You can feel the flow of air in your home say if you just cut a hole into the drywall and put your hand in front of the hole to see how tight your insulation is. I had an issue about 25 years or so ago where I added an automatic attic fan to draw out the attic air during the summer. I had something like 4 ducts in the attic. The fan still was drawing out too much air at the time; noted by the venting over the hot water heater / furnace at the time. It was creating a negative pressure in the house and drawing CO into the home. I added more ducts in the attic to solve the issues. Its similiar when playing with your forced air system; IE: if you draw more air than what you can supply then the air has to come from somewhere.

pete_c said:

I am not sure what the tool was; but there was a device utilized to measure the air flow at the main supply duct. A small hole was drilled into the main duct. Two instruments were used; a flow sensor and a temperature sensor. The temperature sensor was digital and the flow sensor was analogue.

Click to expand...

Drilling a small hole in the duct is to insert a pressure transducer. If you know the pressure you can calculate the cfm's knowing what type of blower you have. The system is designed for an ideal number of cfm's where it works most efficiently at extracting heat/humidity from the air.

For the ducting to work properly you need a certain level of static pressure in the ducts. Without that static pressure, you don't get proper distribution of air throughout the system. If you are in a commercial building with those big round ducts hanging from the ceiling, you notice how after each vent the diameter of tube is reduced. This is to keep the static pressure consistent as you go down the line so each duct has the proper amount of air forced out of it.

And I agree with Ira regarding the minerals in your water. Rain water has very low mineral content, your tap water is likely different. A water softener might be necessary. But for sure you need a low enough humidity and cheap enough water.