Interesting information, but I understand the Rheem Mod is already a decade old. Seems to me, if some huge recall were to happen to it, there would already be rumblings.
Originally Posted by hvaclover
On the contrary, the only complaints I here are from pro's trying to sell competitor's units.
My knowledge of what is available in furnaces and air handlers is limited. However, I do know quite a bit about motors, so perhaps I can contribute something in that area.
PSC (permanent split capacitor motors) are more efficient than shaded pole motors, but I think that shaded pole motors are no longer used anyway. The PSC motors used with blowers often have tapped windings which typically provide 3 or 4 speeds. Generally the motors have 6 poles providing a synchronous speed of 1200 rpm but, because there are not synchronous motors, there is always some slip resulting in a speed somewhat below 1200 rpm. When a lower speed tap is selected to make the blower run more slowly, efficiency is reduced because of the increase in slip. However, because the power required to drive the blower varies with the cube of the speed, running it at a lower speed would reduce the power required even though the motor is less efficient at the lower speed.
The efficient variable speed blowers control the speed by other means. Some use brushless DC motors. Actually, the motors aren't really DC; there is an inverter built into the motor so that the motor is actually running on AC even though DC is provided to the motor assembly. Generally the motors are permanent magnet synchronous motors. They are very efficient at all speeds and generally the speed is controlled by varying the DC voltage to the motor assembly.
Another method to control blower speed uses an ECM (electronically commutated motor) controlled via an external 3-phase inverter and the speed is controlled by varying the AC frequency. Another type of motor that uses an external inverter is the VSR (variable switched reluctance) motor. The VSR motor itself is very simple and has no windings on the rotor. It too is controlled via a variable frequency inverter.
The shaded pole motor is horribly inefficient but cheap to manufacture. The PSC motor is considerably more efficient than the shaded pole motor. The other motors are considerably more efficient than the PSC motor at all speeds and, when the speed is controlled appropriately, will provide more satisfactory performance for the HVAC system. However, the initial cost is greater and it may be that the electronics involved could reduce the reliability. On the other hand, they've been around for a long time and it may be that that has provided sufficient time to work out the bugs and make them reliable.
Others know more than I do about how these devices are used with HVAC systems.
Fairly good analysis of energy saving blower motors. It's five years
old so the utility rates used in the calculations are a bit low.
Good read though.
Anybody as a student who attended a good HVAC school knows all that theroy, but I think it is too deep to present to an HO>
Originally Posted by FRE
Last edited by hvaclover; 04-21-2008 at 09:36 PM.
Too much for some. Others would like to hear that info.
In the end though, if the info makes or breaks the sale, is what matters.
exactly. im a home owner and i want this information. i have spend considerable time researching furnaces because i want to understand what is involved and make a decision i am comfortable with. i also want to have knowledge around some of these details to protect myself from false information or faulty opinions because after all, i am the one that is going to have to live with the machine and installation, not the contractor or manufacturer.
Originally Posted by beenthere
i think buying an extended warranty is a good way to mitigate risks as well.
An extended parts and labor warranty are always smart investments.(factory/third party)
Last edited by hvaclover; 04-21-2008 at 11:47 AM.
Here's some data for you to illustrate power consumption for a VS motor. I don't have example data for a PSC motor.
This data is from a WaterFurnace 3-ton 2-speed compressor variable-speed fan motor Envision unit. It's a 230V ECM2 variable-speed motor.
While the range of data is reflective of the ECM2 motor overall, the specific values are dependent on specific installation. Current draw is shown as a range, as the draw is dependent on static pressure. This data is from a zoned unit, and thus the static pressure varies as a function of the zone damper positions.
ECM2 motor (only) current draw:
0650 cfm: 0.15 - 0.36 amps (200-395 rpm)
0750 cfm: 0.19 - 0.54 amps (263-465 rpm)
0850 cfm: 0.24 - 0.76 amps (270-519 rpm)
1000 cfm: 0.32 - 1.12 amps (308-625 rpm)
1100 cfm: 0.43 - 1.54 amps (333-678 rpm)
1200 cfm: 0.56 - 2.25 amps (363-779 rpm)
1300 cfm: 0.67 - 1.04 amps (385-508 rpm)
1400 cfm: 1.02 - 1.30 amps (472-555 rpm)
1500 cfm: 1.02 amps (454 rpm)
Again, this data should be used just to get an idea of power consumption for an ECM2 motor - the variability shown above is reflective of static pressure changes, and, the Intellizone controller limiting upper speeds to lower static pressure scenarios.
Hope this helps.
yes thats very helpful! i see the current draw is quite low. lower than i expected actually. i understand that the static pressure affects these units but still as a guideline. i can see why its possible to run an ECM motor on low 24/7 without too much utility cost.
Originally Posted by a0128958
As I said in my post, its too much for some.
You have to feel out each individual customer. You can't group all customers together, no more then you can group all HVAC contractors together
Yes, if I were to run my ECM2 motor "on low 24/7" it would cost me roughly .15A * 230V, or approximately 34 watts. Including the standby power consumption for the Envision, at about 30 watts, the total adds up to the advertised "run the fan on ON for about the cost of a 60 watt light bulb" (paraphrasing). So it can be measured, and verified, that yes, running an ECM2 motor on the lowest setting is about the same as the light bulb. So if this is what you were looking for independent confirmation of, you're all set. Indeed, the ECM2 motor is 'the real deal.'
Originally Posted by plexus
But, in my individual case, I don't run my blower motor 24/7 because I don't live in an arid climate (I live in Dallas area). See the numerous threads on this site that address the increased humidity levels that can occur when the blower motor is running with an evaporator coil all loaded up with water without the compressor simultaneously running. In fact, this was the case for me, and I actually measured the RH increase. So for my geographic location, while the advertising of a cost savings of a VS motor running 24/7 is 'catchy,' it's not as comfortable due to increased RH.
Actually, I am a home owner and my degree is in business administration. So, if I can understand various types of electric motors, surely others can also.