Author Topic: The Hunt for High Efficiency: An A/C story  (Read 280 times)

Offline bonneyman

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The Hunt for High Efficiency: An A/C story
« on: May 16, 2018, 10:41:58 AM »
Due to unexpected response I thought I'd start a thread on the industry's search for high efficiency in air conditioners. I'll try and not get too wordy, keep the technical details from taking over, and hopefully explain how all those details translate to the topic at hand. Namely, how much money does newer hi-eff units save the customer.
Let me begin by saying, "You can't get something for nothing!" If you're gonna get something over here, you're gonna have to give something up somewhere else. In all that follows keep that in mind. If you're getting higher efficiency - if - then you're sacrificing something else. You need to figure out what that sacrifice is, and if you can live with it.

I'm going to limit my area of discussion to mostly heat pumps. Gas and electric furnaces are another story, and heat pumps are basically air conditioners that can run in reverse, so - aside from the few items that allow a HP to function (defrost controls, reversing valves, aux heat strips) - all of the efficiency ideas discussed will apply to straight A/C's.

I'd like this thread to be as helpful as possible to you all out there. So please post any questions or comments, or suggestions of what topics you'd like to see discussed. Let's make this a great thread together!

I got into HVAC in 1988. It was an exciting time. The residential/light commercial market had been rolling along since the 60's, and I was able to rub elbows with and learn from those technicians who'd been in the industry for 20-30 years. We were right on the cusp of a bunch of innovations inundating the business, so, I tend to think of the late 80's as the dividing point between how things used to be and how they became. (Roughly analogous to the automotive industry).
When I learned the mechanics it was the "old" stuff (1970's) and the "new" stuff (1980's). If you started in HVAC in the 60's you would have no problem at all working on units in the mid to late 80's. Things didn't change much, and - when they did - it was usually one thing that slowly became integrated. Again, much like auto mechanics. This analogy between cars and A/C's should help everybody understand what we're discussing better.
Cars in the 40's and 50's were "tanks". Who could even spell MPG? Who cared? All folks wanted was power, durability, affordability. And that's what the car makers provided. They didn't get the best fuel economy and they put out too much pollutants, but the engines were powerful, reliable, and easy of the backyard mechanic to fix. Same with HVAC. Older units were heavy, rugged, and made cold air. And the tools to fix them were specialized but not beyond the average mechanic. But they did consume alot of electricity - studies have shown that the biggest electric user in a typical home is the A/C.
In the 70's after the oil embargo car makers began to see government regulation concerning fuel economy, as well as regs for pollution reduction. So they hit the drawing boards, coming up with different things to increase MPG and reduce emissions. This trend only accelerated in the 1980's. The same with A/C. While the Carnot cycle proved heat pumps could actually work back in the late 1800's, it wasn't until the late 1960's that they became economically feasible. Since (in theory) they were more efficient than gas or electric heat they became a big thing in the 70's. It's with this that we'll start our discussion on hi-eff.
« Last Edit: May 20, 2018, 05:41:42 PM by bonneyman »

Offline bonneyman

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Re: The Hunt for High Efficiency: An A/C story
« Reply #1 on: May 16, 2018, 11:12:27 AM »
Heat pumps work on the idea of an air conditioner but running in reverse (the freon flow, that is). Put some water on your arm, and blow on it. It feels cooler. This is because the water - as it evaporates - absorbs heat from your skin and carries it away as a vapor. The exact same principle occurs in an air conditoner/heat pump. Only difference is the liquid is freon, and the evaporation is happening on the inside of a copper tube. So, rather than the heat being carried away from the surface of your skin by evaporation of water, heat is being carried away by freon evaporating into a vapor on the inside surface of the copper tube. So, a heat pump absorbs heat from inside the home (and dumps it outside) in the summer, and then absorbs heat from the outside air (and pumps it into the home) in the winter.
OK, but how does a heat pump extract heat from the outdoor air when it 0 degrees outside? Since freon boils at -41 deg F, it will evaporate above that temperature and absorb heat while doing so. Theoretically a heat pump can thus extract heat from the air down to that low temp, but in practice HP's of old really stopped working around +25 deg F. (Newer units might have pushed that limit down some). Obviously they don't work well when the ambient conditions get that cold or colder most of the time. Auxillary electric heat strips are installed and come on whenever the outdoor temp drops to the point when the HP part of the system can't keep up. In the view of efficiency one really doesn't want the strips coming on at all, as when they do, the surge of electric usage outweighs the efficiency advantage of the heat pump. Plus, when a HP operates, the outdoor coil operates below freezing during certain phases. Any moisture in the outside air will freeze on the coil, restricting the airflow and reducing the amount of heat that can be absorbed. (More reduced eff) A defrost method of some kind needs to be activated to melt that ice buildup when it reaches a particular point. The unit "switches" to cooling, and any heat it makes goes to the outdoor coil to melt the ice. During this time no hot air is coming into the house - though the unit is running full tilt as ever (Again, kills efficiency). 1970's heat pumps were thus designed with some innovations to reduce/eliminate these eff killers.

Defrost timers - originally were mechanical, just like your garden watering timers you can buy. But they were clunky, would wear out, and could easily be duped by changing weather conditions. They typically checked for the need for defrost every 90 minutes. if a temp sensor buried in the outside coil was iced up (and cold enough) the switch would switch the unit into defrost. Simple and cheap design, but not the most efficient. If the sensor was 2 degrees away form initiate point (i.e. the coil was pretty iced up but not quite to the initiate temp) the defrost control would skip the cycle and not check again for 90 minutes. During which time the unit was not working well. Or it might initiate but then stick and not terminate - letting the unit run for who knows how long eating electricity but not heating the home. Eventually the manufacturers went to electronic timers - what we call time/temp boards. Meaning, if the temp was a certain point at a certain time it would defrost - otherwise not. And the lacquer conformal coating on the circuit boards made them fairly resistant to dirt and moisture. Though heat and sloppy manufacturing still plagued them.

Programmable thermostats - Old stats you'd set and go. No problem, easy peasy. but, if you left for work and forgot to turn it off, the heat pump would come on and off all day while no one was home. Killed the electric bill. programmable stats could almost eliminate that problem. You could tailor a program to suit your lifestyle and needs, have the unit come on 15 minutes before you got home and make the house nice and comfy while saving energy all day. Then they tried them in commercial buildings. Worked fine - until someone came in to work over the weekend and the program wasn't set for Saturday. You could unlock the stat so workers could make the adjustment, then someone would set it to 50 degrees and rush off and forget to switch it back. There's goes your electric bill! One maker then built in a 3-hour override feature. An unplanned weekend worker could come in, hit the 3 hour override button, and the unit would come on at the weekday temp setting - and then go off after 3 hours. No more forgetting, and the longest the unit could possibly run with no one in the office was 2 hours and 59 minutes!
« Last Edit: May 18, 2018, 03:59:33 PM by bonneyman »

Offline bonneyman

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Re: The Hunt for High Efficiency: An A/C story
« Reply #2 on: May 16, 2018, 11:27:23 AM »
The 1980's brought a host of improvements toward higher efficiency.

Defrost Controls - the previous time/temps digital boards weren't bad (in fact, for many years I carried a generic time/temp defrost board in my truck, and whenever I had a defrost control problem I'd wire it in and get the unit to work), the engineers did better. they developed the demand defrost board. meaning the board would constantly monitor the HP and only bring it into defrost when it absolutely needed it. And, as soon as the unit was defrosted, it ended the defrost cycle. No waiting for a timer or temp sensor to signal. This reduced somewhat the amount of overall defrost cycles, and saved some energy.

Auxillary heat strip controls - many times whenever one adjusts the temp on their stat more than 3 degrees above the current room temperature the system would say, "Oh, they want all the heat we can make!", and bring on the strips even though the outside temp wasn't low enough to warrant it. makers installed switches - outdoor thermostats - that were wired into the strip heaters, and wouldn't let them come on until the outside temp dropped to a preset setting. Thus, if the HP could heat the home, the OD stat wouldn't let the strips come on - saving money.

Programmable thermostats - stats continued to proliferate and evolve (seemed like everyone and their brother came out with one). One could have a program for the same times and temps everyday of the week (7 day), or different times and temps for weekdays and week ends (5/2) or different every day. One could fine tune the stat to their individual work schedule, kids school, routine meetings, etc. Saved a little more. Then Honeywell came out with what they called "adaptive recovery". Say you programmed the stat to be off all day, and then come on so that by 5PM when you got home it was at 75 deg. You set the stat to come on a say 4:20 to give it the time it needed to drop the temp to 75. Well, adaptive recovery would watch and measure how fast the temp dropped when the unit ran. After a year of learning it would self-adjust the start time. You set it to come on a 4:20 (40 minutes to cool things to 75). The stat learned it only took 22 minutes to do it. It would self-change the on time to 4:38. Thus, the unit ran 18 minutes less per day - all 5 days a week. Over time, those savings added up.

Fan cycling on condenser motors - A/C's need a pressure differential across the metering device of about 100 PSI (that's what it used to be, don't know if that figure still holds) to function properly. If the OD temp is too low (say below 80), the condenser cools the freon so much that its pressure drops below this minimum 100 PSI difference. the evap starves, cooling drops off, and things go haywire. In the old days there were fan cycling switches that were pressure activated. The pressure goes low, ti turns the fan off. When it comes back up, it turns the fan on. the incessant cycling killed the switches and the motors. Then they designed a temp activated two speed switch. Below 90 the fan ran on low speed, above that it switched to high. Better, but still hard on components.

Delay off relays on evap fans - When the t-stat satisfies it shuts the system off. On older systems everything went off simultaneously. Then someone thought: the evap coil is nice and cold at the end of the cycle. Why not install a delay of some sort to run the evap fan for a set time period after unit shutdown and use that cold? By running the evap blower after the compressor shuts off we can extract that cool (that we already paid to make) and pump it into the house instead of letting it go to waste. The time delay relay keeps the indoor fan running for 1 1/2 to 2 minutes after the compressor shuts down. Early switches were Klixon-types of timers, which became more sophisticated timers and finally electronic timing circuit boards. A few more pennies saved!

Thermostatic expansion valves - the original capillary tubes (and the more modern piston metered orifice) fed freon liquid to the evaporator according to back pressure and was limited in it's flexibility. Sure, it was simple and worked fine at design conditions but couldn't adapt to changing heat loads. ("Accurator" pistons were a step up, as one could make fewer cabinet sizes of units, and vary the capacity by putting in a bigger or smaller piston. But they also couldn't adapt past a certain flow rate). Expansion valves could. As temps on the sensing bulb changed, the valve could open or close to match the conditions and needed requirements. As mechanical valves they did wear and could get clogged up with debris but overall became standard equipment. First on evap coils only (cap tubes were still used outside in the HP cond unit ) but eventually most all manufacturers went to TXV's exclusively. To meet every increasing SEER ratings they had to.

Spine Fin condensor coils - unlike most copper tube/aluminum fin coils, Trane's Spine Fin was an all-aluminum design made with an aluminum sheet strip cut into fine threads and attached to an aluminum tube. No galvanic action between two different meats, much less likely to clog, and the much larger surface area afforded by the spines increased efficiency greatly.

ClimaTuff compressor  - although a piston compressor, Trane's ClimaTuff had a host of features that prolonged the life, increased the durability, and overall helped their units achieve consistently higher SEER ratings. The big difference was in its valves. Most piston compressors use hardened steel plate valves that were long and had a relatively thin cross section. (This was to make the most of the steels natural spring action). however, any liquid that inadvertently entered the cylinder had nowhere to go during compression. And since liquids don't compress, steel bends and breaks! ClimaTuff utilized a pair of circular high tension strength steel valves, with a much larger surface area and even distributed around the top of the cylinder. Though not liquid-proof, they were much better at allowing liquid to exit the cylinder undamaged. Added immensely to the lifetime of the compressor.
« Last Edit: May 20, 2018, 12:08:06 PM by bonneyman »

Offline bonneyman

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Re: The Hunt for High Efficiency: An A/C story
« Reply #3 on: May 16, 2018, 11:47:31 AM »
The 90's things continued to improve albeit at a slower pace.

Scroll compressors - a big jump in efficiency! (And they were introduced just in the nick of time, as the SEER rating was raised to 10 in 1996). With piston compressors, no matter how well designed, there's always some compressed gas left in the cylinder at the top of the stroke. This compressed gas re-expanded on the down stroke, wasting energy and reducing the pumping capacity of the cylinder. Through tight tolerances, exquisite valve design, and strict quality control this wasted gas was reduced but couldn't be eliminated. A scroll compressor doesn't have valves. It spirals and compresses gas in a continuous smooth cycle. (An efficiency jump right there). Piston compressors also needed what are called mufflers to smooth out the pulsations of the compression cycle. Scrolls didn't need those, and again, less restriction devices and higher efficiency. Finally, the way scrolls are constructed allows for some lateral movement of the shell surfaces. Liquid doesn't compress, so, designers take great pains to assure no liquid freon gets into the compressor. But during some operating regimes liquid "flooding" is unavoidable. Piston compressors are killed by flooding, with bent rods, cracked valves, and cratered pistons.  Because scroll compressor shells "separate" above a certain pressure, any liquid freon that happens to get that far can pass through safely.
At first they could make the scrolls bigger than 3.5 tons, and they did have a learning curve and weaning problems. But now virtually all HP manufacturers use scrolls exclusively. Though some budget brands still use piston comps.

Dual-compressor units - as the early variable speed compressors were pushing the available technology past its limits, a few manufacturers took a different path - using multiple standard compressors. There were typically two compressors in the unit. A "5 ton" unit would have a 3 ton and a 5 ton compressor hooked in parallel.  Using a special thermostat, the unit would come on in first stage and run for 7 minutes. If the temp stayed the same or continued to rise it would turn off the first compressor, wait a minute, then bring on the larger compressor. Experiments had shown that the first stage could handle the load 80% of the time. Thus you'd be saving energy as you would only be running the full capacity when it was really needed. Smart idea, but there were several shortcomings. First, with two compressors the system was initially very expensive to buy. Second, both compressors shared a common oil line between their crankcase sumps. If one comp burned out it contaminated and killed the other one along with it. Then third, if you needed a compressor change out you had to change TWO compressors! Very expensive to fix.

R-410A - contrary to popular belief, 410a was not designed for higher efficiency. It was mainly an ozone depletion/global warming reducer. In fact, the early 410a units could NOT match the efficiency of R22. It took several years before 410a would exceed R22 efficiency ratings. R410a is a Carrier invention. Let me explain.
In the 90's all the manufacturers knew that R22 - as had happened to R12 - was going to be cutback and finally banned. The EPA hadn't formalized the refrigerant guidelines yet, so, the field was wide open. Every brand came up with  their own refrigerant gas, hoping to get the EPA's approval. carrier came up with R-410a, which won the final approval. After that, the ONLY acceptable refrigerant that could be used to replace R22 in new systems was R-410a. So, every manufacturer - except Carrier - had to re-engineer and redesign their units and manufacturing lines to work with 410a. That took time. During those years, Carrier had a monopoly on the new "eco-friendly" refrigerant. It wasn't until several years later that other brand came out with 410a compatible units.

ECM motors - electronically commutated motors. Typical PSC blower motors are only about 65% efficient. ECM motors are like 90+. So, they use less energy to get the job done. And they add less heat to the already cooled air, so, they're doubly helpful for efficiency. There is no inrush of amps, wiring could be made thinner, lots of advantages. But I was skeptical. Though ECM technology was invented in 1969 by GE, it wasn't until around 1994 (and Chinese manufacturing) that they became viable to the consumer market. They were super high tech - with all the associated problems and growing pains. And my skepticism has been borne out. ECM motors are now like on their 3 or 4 generation because the originals were plagued with problems. There was a push with variable speed compressors, but the cost and technology at the time proved too ungainly to mass sell.

« Last Edit: May 18, 2018, 04:37:38 PM by bonneyman »

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Re: The Hunt for High Efficiency: An A/C story
« Reply #4 on: May 16, 2018, 11:56:02 AM »
2000's - technology improves somewhat.

Rifled tubing - R410a is a totally different animal than R22. First, the operating pressures are 50-70% higher. Trying to use R22 spec'd tubing in the units proved problematic. Though on paper 410a is thermodynamically more efficient than 22, it took a while for the engineers and manufacturers to design equipment to take advantage of this fact. Rifled tubing was one such innovation. (I wanna say it came out right around 2000 or so. Can't remember.) The copper tubes are rifled on the inside with grooves that look eerily similar to that on a gun barrel. 410a is a smaller molecule than 22, so, when used in a 22 tube, the 410a molecules in the center of the tube don't absorb as much heat as they could - because they're not having much contact with the inner tube wall. Making the tubes smaller and rifling them caused turbulence and allowed 410a molecules to have more contact with the tube surface and absorb more BTU's - taking advantage of it's higher thermal efficiency.

Whisper fan blades - typical condensor fan blades "slap" the air hitting them forcing the air upward to expel the heat absorbed in the unit. This makes for alot of noise. A design of blade known as the Cobra introduced a slim, swept shape to the blade that allowed it to slice through the air easier and more gently push it up. This cuts the noise of the fan by 10X - but also reduced energy consumption in the motor! Needing every point they could get manufacturers started putting them on. Smaller motors to get(almost) the same airflow meant less electricity. Not only that, but lower condensor temps leads to lower freon pressures and that means less work for the compressor and even more savings of energy! What started as a quest for quietness leads to that and smaller electric bills if designed wisely. they are such an innovative idea that aftermarket companies are making them as generic replacements for older units.

ECM's - With the SEER rating being raised to 13 in 2006 manufacturers were forced to push technology to the limit in order to stay in business. One such way was putting ECM motors in every application. Complex electronic boards that were originally factory set were made field adjustable to get every point of SEER out of a unit. Both evaporator and condensor motors started going to ECM style, and compressors were heading that way.
Also, ECM's began to be incorporated into the design of the units from the very start - rather than just replacements for PSC motors. Originally, a unit footprint would have the components laid out in a particular way. The blower motors were usually before the evap coil. (Not always but often). With the "invention" of ECM motors, high SEER models would just put the ECM in the original PSC motor location with no thought to design. In the late 90's early 2000's that changed. Now evap motor placement is specifically ECM and it's AFTER the evap coil. On HP's in heat mode this location gets hot, as hot air is coming off the coil. Since the ECM is 90%+ efficient, it can survive that hot location. A 65% eff PSC motor won't. So - if you didn't have the right ECM motor handy - you couldn't swap a PSC motor into it's place like we used to do, as the ambient air temp would overheat it. The engineers did things in such a sneaky way as to thwart field modifications by savvy techs.

Wireless thermostats - everybody loves fancy digital stuff, so, why not make thermostats in that configuration. The early styles were a bit cumbersome, but found a market among tech savvy consumers. You could program a set schedule but could easily log in to your stat from work or on a trip and change the temps or the times to accommodate an unexpected change of plans. If you were savvy enough, and the stat/system was configured properly you could maximize savings. At first not many companies did these, and those that did were on a learning curve. But they did offer some advantages.

Micro-channel coils - an all-aluminum coil design (came out around 2006?) that looks very much like a car radiator. Specifically tailored to 410a, it has smaller passage ways to take advantage of 410a's thermodynamic properties. (It is thus not retro-fittable to older units). It also avoids galvanic corrosion of older copper/aluminum coils, and is made in one piece, to minimize leaks. But they had serious leak problems when the coils first came out, caused by formicary (ant-like) corrosion, which is supposedly the result of chemical attack from household items like hairspray, cosmetics, and cooking vapors. They also are restricted to water only cleaning - only recently has a cleaner been devised that will not corrode the aluminum surfaces.
Apparently, this was the only way manufacturers had left to reach the new 14 SEER minimum, so they adopted the coil design despite the shortcomings (Though, Trane's all-aluminum Spine Fin coil somehow manages to meet the standard, and so Trane is the only brand I know that hasn't adopted the micro-channel coils in their units)
« Last Edit: May 18, 2018, 04:24:41 PM by bonneyman »

Offline bonneyman

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Re: The Hunt for High Efficiency: An A/C story
« Reply #5 on: May 16, 2018, 12:38:44 PM »
2010's

Inverters (ECM compressors) - capable of ramping up or down to perfectly match the needed capacity makes these ECM-style compressor as popular as their predecessors, though the newer electronics are quite sophisticated and require extensive training to work on. Additionally, the board's carry a 10 year warranty. Whether that means the manufacturer trusts it that much or needed to offer one that long to sell the $$$ of the unit remains to be seen. but the wiring it thin, the inrush is almost non-existent, and the amp draw at full load is 1/3 to 1/2 what an older compressor run amps are. Combined with a fully ECM indoor blower and outdoor fan the savings in electricity can be substantial. Though the initial cost of the system means many years of savings to balance out that cost.

Wireless thermostats -  all the name brands are coming out with controllers on the wall in place of thermostats. And being wireless means the new control can be put in even old homes as no new wires need to run to the unit to connect it. It's gotten to the point that a technician just needs to go to the hallway controller, punch in the pass code, and read all the current specs of the operating unit. he almost doesn't need to go to the outside unit to take readings and pressures. (Well, he still has to go out there to physically vacuum and clean the unit!) Customers themselves can access this information, though, for the average person most of this data displayed is Greek.

Electronic expansion valves - in the never ending quest to meet ever more stringent efficiency standards manufacturers are going more electronic. Thermostatic expansion valves respond to a change of temperature on the suction line, the outlet of the evaporator. The temp there is a great indicator of how well the evaporator is doing it's job. Though thermal valves take some time to respond to changes. Electronic expansion valves have a tiny motor in them that spins at incredible speeds, and are capable of opening and closing the valve points at up to 1600 a second! Thus, they have very fine freon flow control. And they can change that flow every second to respond to the smallest change. they manage to squeeze some more efficiency out of the system though they've had plugging issues (which the manufacturer blames mostly on faulty installation).

ECM condensor motor - electronics don't like heat. And ECM electronics are no different. That's why ECM's in the condensor fan application have been slow to implement and reliability have been a problem. Apparently the latest generation of DC, permanent magnet condensor motors are actually working and lasting.

Home integration - the latest thing is the whole home concept. People are clamoring for everything in the house to be connected - the A/C with the lighting and everything else. Peoples hot water heater are connected to the HVAC system, lights are going straight LED to reduce heat load, sensors are everywhere, opening and closing drapes to keep out sun/keep in heat to save electricity. I've seen pool heaters that are basically HP's. Polarized glass use is up, being turned on with a switch to let you have a view when you want but privacy and reduced heat infiltration when desired. All could be interconnected with the thermostat controller, and adjustable remotely by app.
« Last Edit: May 16, 2018, 03:34:47 PM by bonneyman »

Online Matt_T

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Re: The Hunt for High Efficiency: An A/C story
« Reply #6 on: May 16, 2018, 03:43:26 PM »
Excellent write up thumbsup2 thumbsup2

I worked for an hvac manufacturer during an copper to aluminum tube transition. Never once heard efficiency or SEER or COP mentioned. Only ever heard negative comments about long term reliability. Cost was the driver.

ECM motors are basically just DC brushless. Same tech as Milwaukee Fuel powered by an AC>DC power supply instead of a battery.

Inverter is the rest of the world name for a variable frequency drive, aka VFD, used to power a three phase motor. Same tech people use to run 3 phase machinery on residential single phase power. At least that's the technical definition though the marketing department might be putting "inverter" stickers on dc brushless ECM motors th-wink

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Re: The Hunt for High Efficiency: An A/C story
« Reply #7 on: May 16, 2018, 06:51:41 PM »
Excellent write up thumbsup2 thumbsup2

I worked for an hvac manufacturer during an copper to aluminum tube transition. Never once heard efficiency or SEER or COP mentioned. Only ever heard negative comments about long term reliability. Cost was the driver.

ECM motors are basically just DC brushless. Same tech as Milwaukee Fuel powered by an AC>DC power supply instead of a battery.

Inverter is the rest of the world name for a variable frequency drive, aka VFD, used to power a three phase motor. Same tech people use to run 3 phase machinery on residential single phase power. At least that's the technical definition though the marketing department might be putting "inverter" stickers on dc brushless ECM motors th-wink

From what I got in the 5 hour class, the inverter "unit" takes 240 volts AC, converts it to DC volts, and then adjusts the pulses of current that it sends to the "compressor". I guess that would be frequency modulation?
All I know is that it can't be all that efficient, because the huge heat sink on the back of the control board extends into the condenser area(!) so air can be pulled past it to cool it. And with how people typically take care of their units - I'm seeing that heat sink getting all clogged with dirt and leaves and the board overheating. And that won't be covered under warranty. :P
« Last Edit: May 16, 2018, 06:55:17 PM by bonneyman »

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Re: The Hunt for High Efficiency: An A/C story
« Reply #8 on: May 16, 2018, 07:22:34 PM »
From what I got in the 5 hour class, the inverter "unit" takes 240 volts AC, converts it to DC volts, and then adjusts the pulses of current that it sends to the "compressor". I guess that would be frequency modulation?
All I know is that it can't be all that efficient, because the huge heat sink on the back of the control board extends into the condenser area(!) so air can be pulled past it to cool it. And how people typically take care of their units - I'm seeing that heat sink get all clogged with dirt and leaves and the board overheating. And that won't be covered under warranty.


It creates a high frequency output, from the DC bus, which approximates the sine wave voltage and frequency required for the commanded speed. This is usually calculated from a linear Volts to Hertz ratio. So for a 230v 60Hz motor at half speed it's simulating 115v 30Hz. Further reading at the following link:

http://www.vfds.org/vfd-pwm-waveform-762549.html

You're correct in thinking that VFDs are inefficient, compared to a contactor, at full speed on three phase motors. I don't know how the efficiency of a VFD compares to a single phase motor. Figure on a 5-10% loss, using three phase numbers, depending on the drive. The efficiency improvements come from the ability to run at reduced speed where power consumption drops off dramatically as speed reduces in pump and fan applications. Google "fan affinity laws" for more in depth explanations.

And yes keeping these drives cool is very important. Excessive heat build-up will shorten life and might also "randomly" trigger built in thermal protection.
« Last Edit: May 16, 2018, 07:30:05 PM by Matt_T »

Offline slip knot

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Re: The Hunt for High Efficiency: An A/C story
« Reply #9 on: May 16, 2018, 11:10:38 PM »
I've been reading about the inverter technology that's driven the mini split popularity. I've been considering trying one out in a rental unit. kinda giving it a tryout without me actually having to live with it. grinx

Any thoughts on the mini splits. My commercial AC guy from work suggested the MrSlim sets from Mitsubishi IIRC. he's tried some and they seemed to be working ok for his applications.
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Re: The Hunt for High Efficiency: An A/C story
« Reply #10 on: May 16, 2018, 11:48:46 PM »
I've been reading about the inverter technology that's driven the mini split popularity. I've been considering trying one out in a rental unit. kinda giving it a tryout without me actually having to live with it. grinx

Any thoughts on the mini splits. My commercial AC guy from work suggested the MrSlim sets from Mitsubishi IIRC. he's tried some and they seemed to be working ok for his applications.

Personally, I wouldn't put a mini-split on a dwelling. Added cooling on an enclosed garage? Sure. Help to cool the shop? Fine. At the office? Sure. But personal living space? No. I don't trust their durability enough to risk having one on my home.
A rental? Ehhhh. So long as you don't mind an angry phone call in the height of summer - I'd say maybe.
They're not repairable as far as I can see - they are made to use up and throw out. Like new window units. Disposable. JMHO.

Online Matt_T

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Re: The Hunt for High Efficiency: An A/C story
« Reply #11 on: May 17, 2018, 01:27:41 AM »
I'm not sure a mini split makes sense from a landlords perspective. Tenant gets the benefits and you get the bill. And that goes double for Mitsu. The only benefit you might see with Mitsu is improved reliability which is a crapshoot on one unit. Really hard to say without more details. And knowing whether you're willing to do the install yourself.

Offline bonneyman

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Re: The Hunt for High Efficiency: An A/C story
« Reply #12 on: May 17, 2018, 12:00:14 PM »
Mini-splits were originally designed and built so historical buildings could get A/C without major demolition (i.e. destruction) of historical structures. (Let's face it - most historical buildings don't have duct work, or don't have areas where duct work can be installed to use a normal A/C system. And people were against added furdowns and tearing holes in ceilings and walls to install evap units and ducting). Mini-splits were also an attractive option for "spot cooling" where the aforementioned modification was unaffordable - like small homes converted to offices or computer rooms.
Enter the mini-split. All you need is one 4" hole, and everything the system needs to work (both reefer lines, t-stat and power wiring, and condensate drain tube) are routed thru that one hole. A nice neat evap unit hung on the wall near the ceiling line, and with a remote control you could have spot cooling. (Now mini-splits have evolved to the level where 1 condensing unit outside can run up to 5 separate evap units inside).

All of the above structures are for temporary use - nobody lives and sleeps in a monument or office or computer room (well, maybe some people). If the unit failed nobody's gonna die. (They just close the museum or office for that day). Nowadays people are putting mini-splits everywhere because they're cheaper to install than central air and almost any handyman can install it. And they're putting them in babies bedrooms, the indigent mom's room, enclosing a garage so junior can move back home, etc. If the unit fails that's a bad thing!
« Last Edit: May 20, 2018, 05:36:21 PM by bonneyman »

Offline bonneyman

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What can I do to increase my A/C efficiency?
« Reply #13 on: May 17, 2018, 04:29:19 PM »
I started this thread with the idea of letting you guys in on the various so-called advances that engineers have made to their units to increase their efficiency. It's probably most helpful for those of you who are looking into getting a new A/C soon. But what about the rest of us? What about all the 5-10 year old units out that are already out there? Is there anything I can do that will increase my systems efficiency and save me some energy dollars?

The answer is, YES! There are alot of little things that a homeowner can do that will help boost your existing units efficiency and cut your energy bills. None of the following suggestions will make you rich, but they will save you some money. How much? That depends. Every unit is unique, every situation is different. The more effort you put in, the more savings you're likely to get out.
And I'm not promising anyone results that I have not personally done myself and/or saw the results of. All of these tricks I have used at one time or another on actual systems, my own or my customers. (Unless otherwise noted - there are one or two tricks I'm waiting for the chance to try).

First off, if you have a company give you an estimate for a new unit, and claim it will cut your electric bill in half (or whatever)- GET IT IN WRITING! Salesmen say all sorts of crap to get your signature, making all sorts of promises. Then, when those savings don't materialize, you get the unanswered phone in their office! I've told many customers who were getting quotes tell me how much they were promised to save, and I told them have the salesman write that up. They either have the guy say the office will send them the form (and they never hear from them again) or that company policy doesn't permit them to guarantee results. Then why do they say it? They want your signature on the bottom line....and you want theirs!

OK, practical energy saving tips. I put them into tow catagories: passive and active. Passive tricks are those that you do to reduce the heat infiltration into the house in the first place. Active tips are things you do to the system to help it remove more heat per hour of operation.

Passive tips
Obviously, the best way to keep your house cooler is to keep as much heat out of it in the first place.
For that:
1) Install/replace weatherstripping on all outside windows and doors. Installing reflective film on the glass helps too if you aren't going to miss the view.
2) Paint the house a lighter color (HOA's may make this difficult)
3) Paint the roof with a quality reflective coating - White or light colors help, but you really want to make sure the coating contains titanium dioxide. It's a white crystalline substance that reflects both visible and infrared (i.e. heat) wavelengths. And you want domestic-made TiO2 - Chinese and Indian is not as good.
4) Plant trees and shrubs around the south and west sides of your home if possible. The shade they cast will help keep some heat out of your home. Maybe not the first year or two - but as the trees grow year after year you'll get more shade and maybe be able to offset some of the ever-rising utility costs.
5) Check/replace the black foam insulation on your refrigerant lines. Especially if those lines run thru the attic! Any heat infiltration into the freon lines means more heat the system has to get rid of, and hot attics can add alot of heat to un-insulated or poorly insulated linesets. Stuff is cheap to buy and not hard to put on - just some sweat crawling around in the attic!  lolx
6) One area that most technicians miss is keeping the condenser cool. (The outdoor unit that houses the compressor - if you have a split system). Freon has a temperature/pressure relationship that is relatively linear. When one goes up, so does the other. When one goes down, the other follows. So - if you can reduce the heat beating on the condenser unit coils - you will reduce the freon pressure as well. And anything you can do to reduce the head pressure reduces the load on the compressor. Then it's amp draw drops, and that means energy savings! If you're lucky the condenser will be on the north side of the house. If you're unlucky like I am, it's sitting on the south wall! One solution is plant some shrubbery around the unit. Not so close that it impedes the airflow (that will negate what you're trying to do). And you want to choose plants that don't shed leaves or needles - those tend to clog the coil (again, a bad thing). Or you could construct a perforated wall around the unit. Unit coils are typically silver or black, so you want to keep the blazing sunlight from hitting the coil. Construct your wall from wood lattice sheets that are offset inside to outside. You should be able to make it so air can flow freely through the openings but the sunlight is blocked! Mount it close enough to the unit so sunlight hitting the coil is minimized. Paint it white (so it doesn't heat up the air that's flowing thru it) and whatever you do don't put any kind of cover on the top of the unit (the air exit). Keep at least 6 feet above the unit unobstructed. Finally, make sure the wall can be removed for easier cleaning and servicing of the unit.
Since installing such a shield on my system I've kept the electric bill from climbing dramatically year after year. It's still climbing (my power company is money hungry!) but it's rising slowly. And the $40 worth of wood and paint is well worth it.
« Last Edit: May 17, 2018, 05:26:58 PM by bonneyman »

Offline bonneyman

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Re: The Hunt for High Efficiency: An A/C story
« Reply #14 on: May 17, 2018, 05:00:29 PM »
OK, now for some more involved (and more expensive) active tips:

1) Make sure your system is serviced and cleaned by a reputable company. You want to make sure the duct-work is clean, the filter is clean, and the coils are clean. Proper airflow is critical to system efficiency and operation - especially any system higher then 10 SEER. Those hi eff units get alot of savings from newer blower motors that depend on and require low static pressures to deliver their rated SEER. Older systems motors would "push" the air thru a less-than-optimal system. Newer 12 SEER and up units aren't so forgiving.

Have the technician inspect the wires going from the circuit breaker to the unit. Many times the original wire size were not upgraded when a new install was done. Too small a wires can cause a host of problems - if your lights dim when the compressor comes on you almost certainly have a wiring problem. Make sure the wire ampacity is sufficient for the AC.

2) See if you can upgrade your filter system. Most homeowners have 1" thick filters. But many newer installs had filter bases that were field-convertible to 2" or even 4" pleated filters. If you can up-size, then, by all means do so. You get more filter surface area, and (with outside dimensions being equal) lower pressure drop, and better overall airflow characteristics with thicker filers. Most homes are woefully undersized on the filter - and it usually doesn't reveal itself until the new hi-eff unit is installed! lol
I give you my calculated estimates when I go to a house and suspect undersize filters
2 ton needs 383 square inches of filter surface. That equals a 20x20x1 filter (approx)
3 ton            576   "           "                                                       24x24x1
4 ton            792   "           "                                                       28x28x1
5 ton            959   "           "                                                       31x31x1
The largest commercially-available filters are like 20x25x1 (500 sq. in.) and 25x30x1 (750 sq. in.), and most homes' return grille won't hold 2 filters. My SIL has a 3.5 ton system, and she changes (2) 20x25x1 filters each month. You go girl! thumbsup2
         
3) Add a lubricity enhancer into your sealed-system. I use a product called Supco 88. Invented in 1954, it mixes with the oil and helps clean internal valves of varnish (from old, decayed oil) as well as making the oil more slippery. About $20 for the bottle, any tech can inject it safely for you. But it's for mineral oil (R22) systems only. Here's a link with some info downloads:
http://www.supco.com/web/supco_live/products/S8.html
The newer product is Zerol Ice - now called AC Renew. For any oil. The Renew has the added benefit of helping to keep the oil vapor (that circulates with the freon) form thickening and clumping onto the inside surfaces of the evap coil tubes, hindering heat transfer. It's $125 for the treatment, lasts the life of the unit. They both help to free up tight bearings and reduce amp draw in the compressor, saving money. I've used both - the Renew gave my customers and average of 5-7% reduction in electric bills per month.
*** Lots of people say these two things are snake oil. My response is - you'd don't have to use it!***
http://www.nucalgon.com/products/oils/a-c-re-new

4) Always get a unit with a Scroll compressor, and if you ever need to replace a compressor, install a Scroll. Any technician worth his salt can make the necessary adjustments from a OEM piston comp. The Scroll costs more money upfront, but it's much more efficient and - if you're going to be in the home for awhile - will pay for itself.

5) If you need a new condenser fan motor (chances are at some point you will), try and get an 825 RPM replacement for a 1075 RPM OEM model. Slower speeds means a little less less amp draw. You'll have to change the fan blade too (a good idea anyway, because they usually wear together - and getting an old blade off unharmed is tough!) and there are available charts to guarantee the new slower speed blade moves enough air. I had to do a trick like this, as the OEM parts were NLA. Worked a bit better than the original set-up. thumbsup2

5a) To be really slick, change the paddle blade fan to a Cobra blade. Much quieter, and more efficient. (Wanna try this myself!)
http://www.lauparts.com/Products/HVAC-R/Propellers/Cobra-Blade
« Last Edit: May 20, 2018, 12:09:32 PM by bonneyman »

The Garage Gazette

Re: The Hunt for High Efficiency: An A/C story
« Reply #14 on: May 17, 2018, 05:00:29 PM »