heat wheel with economizer

[ceng]

For Ahus serving classroom, gym, offices under north ohio public school systems, it requires those units have both heat wheel and economizer. Any one familiar with those? How those are controled? Please advise. Thanks!

[sirhc]

Are you possibly talking about an Energy recovery ventilator(ERV)?

[gruvn]

Typically the wheel will receive a 0-10 signal, and be controlled by the BAS, the economizer cycle doesn't change. What brand of air handler and what brand of wheel ?

Does the wheel have a VFD ?

If it does, is the VFD for operation or just for defrost ?

[jamcontrol]

Originally posted by ceng
For Ahus serving classroom, gym, offices under north ohio public school systems, it requires those units have both heat wheel and economizer. Any one familiar with those? How those are controled? Please advise. Thanks!

The economizers work as normal: OAT < RAT, enable economizers to modulate. There comes a point where OAT is too cold and economizers are at minimum then you want to enable the heat recovery wheel, say OAT < 32F. Then you can modulate the heat wheel to maintain SA temperature with a EA temperature (15 F) low limit restriction.

During the summer when OAT > RAT, you can run the heat wheel at max.

Hope this helps.

[Control Man]

Did 20 units for some casinos a few years ago and the sequence was pretty much as jamcontrol noted

[gruvn]

Heat recovery wheels should run all the time, that the unit does, if you are shutting it down you are ruining the wheel.

[ceng]

why if we shut down the wheel, we'll ruining the wheel? I am not good at wheel at all. Is this for freeze?

[Freeze Stat]

If air is passing over the wheel it should be turning. Most wheels are somewhat self-cleaning while they are turning. If they are stopped and air is passing over (or through) them, dust and dirt will eventually clog the wheel. This can cause the wheel to be un-balanced, it can reduce air flow and just generally screw everything up. A few years ago, we built some rooftop units with heat wheels for schools in Ohio. These units had bypass dampers around the wheels. Whenever the wheel was not in operation the dampers opened and the wheel was bypassed.

[jamcontrol]

Sometimes an engineer designs it with filters on the OA intake and RA ducts. This should protect the wheel from getting dirty but the filters should be changed regularly.

[ceng]

Thanks for all of you. It seems we are on the right track. We have the filters on both oa and return and we have the by-pass damper on both the path of the wheel. Once again appreciate all of your help!

[mechdesigner4controls]

Consider this for starters;

Energy Recovery Wheel
1)A control panel, provided by the energy recovery wheel manufacturer, shall control the energy recovery wheel speed when the supply and exhaust fans are in operation.
2)Energy Recovery Wheel Control (By Energy Recovery Wheel Manufacturer): If the outdoor enthalpy is less than the exhaust enthalpy, the wheel modulates to maintain the supply temperature setpoint. If the outdoor enthalpy is greater than the exhaust enthalpy, the wheel rotates at full speed (20 RPM) in summer cooling mode. If the outdoor enthalpy is less than the exhaust enthalpy but the outdoor temperature is greater than the supply setpoint, the wheel will rotate at minimum speed (about 0.2 RPM). The controller will automatically calculate an exhaust temperature condensation control setpoint based on the space humidity. If the exhaust temperature drops below the condensation control setpoint, the wheel will modulate slower to maintain the exhaust setpoint. The wheel receives the minimum signal from the supply temperature and condensation control loops. A VFD is used to control the speed of the energy recovery wheel, which determines the supply temperature. The speed of the wheel is proportional to the 0-10 volt signal generated by the Energy Recovery Wheel DDC controller.
3)The Energy Recovery Wheel shall be interlocked with the supply fan via hardwire interlock.
Are there temperature and humidity sensors on each side if the wheel ?

[ceng]

mechdesigner4controls, thanks for all the input. They are very helpful. For my system, we have both economizer and wheel. So I am not sure if we'll have such a complex whell control. We won't have VFD for wheel for sure. I am pretty sure we will have both temp. and humidity sensors on either ends. But how to program them, I have not totally figure out. Once time comes, I might pdf my control diagram and sequence and ask more help. THanks again!

[icepik]

Typically the heat wheel speed is modulated based on the supply temperature, and over-ridden by the exhaust freeze sensor. I've only seen make-up air units with wheels, but I suppose the wheel could be turned off in the summer to allow the economizer to function.