DIY ventilation heat exchanger

[AC_Hacker]

Originally Posted by KiwiMark

Sorry to waffle on... maybe pictures to follow.

Thanks for the description of your HRV project.

Yes, your pictures would be most welcome.

If you click the "edit" button, and (sometimes) you need to click the "go advanced" button, it will take you to a page that will easily enable you to upload photos. If you go to the "manage attachments" button, you can browse to your photo(s) and then click the "upload" button to get your pix onto the server. Once this is done right-click on the hyper-linked image reference and do "copy link address". This will allow you to then use the picture attachment button, using the file reference already on the server. It's easier to do than to explain, but your images will be in-line, look really cool, and be available for the duration of the EcoRenovator blog.

Best Regards,

-AC_Hacker

[AC_Hacker]

Dave,

On page 20 of your "Homemade heat Recovery Ventilator" PDF, you mourned the passing of your favorite fan:

After more than six years of faithful service, the intake fan motor wore out.

I read of someone working on a very different project having the very same problem. In this case, he was trying to data-log the temperature of the outdoor air at his residence, and he took the 'maximum technology' approach and affixed a small diameter, dual-ball-bearing computer fan to blow through a 3"diameter ABS tube, within which was a digital thermal monitoring device. The fan, itself was reputed to have a life of 5 years continuous use, but it bit the bullet after half a season. His analysis of the situation was that the fan was designed for a computer environment, where it was working in warm dry clean air. But in his application it was exposed to a moisture-condensing environment with quickly wrought it's ravages on the little fan. His fix was to use a centrifugal fan, the design of which kept its motor outside the condensing-moisture air-stream. Problem solved.

In your paper, you refer to the option "dual centrifugal fans" as are found in range hoods. These fans, if designed properly, move the motor and it's bearings outside the hot, humid bacon fat laden air-stream, or in our case outside the condensing moisture air-stream.

Regency Dual Blower (NOTE rubber mounting spacers)

I think the dual centrifugal fan would remedy the problem of too-short fan life.

What do you think?

-AC_Hacker

* * *

[jrandom_EE]

Wow, I just wanted to compliment you guys on an awesome thread! I've been looking at how to design an air-air heat exchanger, with particular focus on recovering the latent heat of vaporization as well as the sensible. It has been very elucidating to read the thread, and interesting to see that other people have thought of using a computer case fan as well! (I would think that if you put the fans on the dry side of both streams, it would work better?) Series is also possible, computer case fans are cheap so worth looking at perhaps. Some googling for "static pressure" computer fans yields that Yate Loon fans might be a good option. Apparently they make centrifugal computer fans as well.

I've been wondering how hard it would really be to design an energy wheel type ERV. These types are noted for not lasting more than a year or so. But maybe that's not a problem.

Although I'm an engineer I'm a novice at this. However, I can't help but think that if you can get an electric motor to turn at the appropriate rate and build a wheel, and build the wheel housing for easy disassembly, you'd just use crystalline kitty litter for the heat and water transfer medium. Crystalline kitty litter is just silica gel. With $20 worth of materials, you could choose to either turf the kitty litter every year, or perhaps just hose it down? Or filter the ends? It's cheaper than buying good filters.

For filters, I'd design it to incorporate some of the IQ air filters. The IQ air is the premium air purifier on the market, using a prefilter (mainly pollen), a VOC filter and a hyper HEPA filter (in that order), it filters pretty much all the crap out of the air in one pass, making it ideal for HRV or ERV requirements. I have had one for several years, it is worth every cent. The pre-filters run about $60, which would last maybe a year or so, but meaning the inside would be pretty clean.

Thoughts?

(Note, I wanted to insert a couple of links or images, but need to get my post count higher! I guess I'll try and post some more. Or something.)

[jrandom_EE]

Just having a look around at ebay, it looks like the options for fans are either:

• Axial flow CPU/PC case fans, maybe in series? Advantage: cheap
• Centrifugal flow PC case fans (no experience with them)
• Centrifugal flow blower, as used by pot growers^H^H^H^H^H^H^H^H^H^H^Hhome hydroponics enthusiasts. Disadvantage: Cost $150 or more, use more power/higher CFM than probably necessary, probably noisy.

I'd just put this out there too - can anyone think of an appropriate motor for the wheel?

[AC_Hacker]

Originally Posted by jrandom_EE

Just having a look around at ebay, it looks like the options for fans are either:

• Axial flow CPU/PC case fans, maybe in series? Advantage: cheap
• Centrifugal flow PC case fans (no experience with them)
• Centrifugal flow blower, as used by pot growers^H^H^H^H^H^H^H^H^H^H^Hhome hydroponics enthusiasts. Disadvantage: Cost $150 or more, use more power/higher CFM than probably necessary, probably noisy.

I'd just put this out there too - can anyone think of an appropriate motor for the wheel?

jrandom_EE,

I really like your thinking about the enthalpy wheel ERV. There are also enthalpy type HRVs that use a permeable membranes to put condensed water back into the air.

Also, I think the right fan will be important. My interest is in case fans because if the very low cost, fairly high quality and also, for me the low CFM. I know that in Europe in general and Germany in particular, using variable speed fans is very important in order to get an acceptable level of performance at a minimum level of energy consumption.

European energy seems to be about 2x the cost compared to the states, and the sophistication of technology is also about 2x.

So, about a year ago, I bought a small mini-split heat pump that had 'inverter technology'. That is the trade name for rectifying the line AC into DC and then turning the DC back into AC, only with a variable frequency. This is used to control the speed of the compressor and also the speed of the fans, both inside and outside. Very quiet and efficient.

So on the outside unit, they use an axial fan, where the noise will not be so much a problem and on the inside unit they use a variable speed fan that is like a squirrel-cage fan, only the squirrel-cage is stretched out. It works really well.

Something like this would be perfect.

I have seen fans like this used in laser printers, but I don't know if they would be easy to control.

With all the developments in 'inverter technology' heat pumps, I just bet that there is an IC that would greatly simplify fan speed control.

Parallel to this line of thinking, I have found out that there are computer case fans with:

• two wires (volts and ground)
• three wires (volts, ground, sense)
• four wires (volts, ground, sense and PWM for controlling speed)

I just bet there is an Arduino out there looking for a fan speed control project.

What do you think?

-AC_Hacker

[NiHaoMike]

If the fan motor has a resolver, it is just a matter of decoding the signals into the signals that drive the motor. Speed control is by PWMing the outputs on and off. For closed loop operation, the controller monitors the resolver signals.

The 12cm ECM fan assembly I have recently stopped working, and the inverter board broke into pieces while I tried to take it apart so I don't know exactly what's wrong. It had a PIC12F508, 4001 NOR array, two MOSFETs, and a lot of surface mount components. I just soldered some wires to the stator coils and resolver IC, then built a simple drive circuit consisting of two MOSFETs and a few passive components. It actually ran better than with the overcomplicated inverter board.

[AC_Hacker]

Originally Posted by NiHaoMike

...built a simple drive circuit consisting of two MOSFETs and a few passive components...

Sounds great.

Got a schematic?

-AC_Hacker

[AC_Hacker]

BTW...

This is very off topic, but here's an interesting How-To:

How to Convert a Computer ATX Power Supply to a Lab Power Supply.

-AC_Hacker

[NiHaoMike]

Originally Posted by AC_Hacker

Sounds great.

Got a schematic?

-AC_Hacker

I just connected the resolver output signals (internally buffered) to the gates of the MOSFETs. The MOSFETs simply drive the two stator coils (2 phase unipolar motor) with two 1uF capacitors as snubbers. The method of control is very basic and does not allow for variable speed, nor does it offer features like inrush current limiting or overload protection. I'm going to design a better control circuit later on.

[jrandom_EE]

Originally Posted by AC_Hacker

jrandom_EE,

I really like your thinking about the enthalpy wheel ERV. There are also enthalpy type HRVs that use a permeable membranes to put condensed water back into the air.

Thanks. I know about those too, but have no idea how I'd design one. But as for the enthalpy wheel ones, they look to be not too hard - just search for the right motor. I'd love to know what their main failure modes are.

Also, I think the right fan will be important. My interest is in case fans because if the very low cost, fairly high quality and also, for me the low CFM. I know that in Europe in general and Germany in particular, using variable speed fans is very important in order to get an acceptable level of performance at a minimum level of energy consumption.

Most probably. PWM is not a bad idea. If you can't get PWM and high static pressure, you could have several of them in parallel with a one-way valve after each, so you'd have several different settings. Or vary the voltage. When I get 5 posts up I'll start posting some links I've found.

I suspect that dust problems can be solved with filtration and humidity problems could be solved by sticking the fans on the "dry end", whichever that is.

With all the developments in 'inverter technology' heat pumps, I just bet that there is an IC that would greatly simplify fan speed control.

Parallel to this line of thinking, I have found out that there are computer case fans with:

• two wires (volts and ground)
• three wires (volts, ground, sense)
• four wires (volts, ground, sense and PWM for controlling speed)

What do you think?

Not sure. Given how cheap CPU fans are I was thinking simply have several of them and use on/off on each of them, as said above. Also, sizing the fan to the application rather than having to step it to the right level. But being able to adjust it would be a plus. I guess I'll cross that bridge when I come to it.

I think first getting an idea of the appropriate static pressure needed would be a good first step. Make a manometer tube, use an oversized fan, and block it until it gives the right flow rate. A simple hack method of measuring would be using a cylindrical outlet and wafting smoke from an incense stick down it, and calculating the CFM from the rate of movement of the smoke. Then use that to look up the right fan.