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Controlling an energy recovery ventilator (ERV)

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    Controlling an energy recovery ventilator (ERV)

    I just purchased a Stirling Technology RecoupAerator 200DX that I'm trying to decide how to control. For those that don't know, an ERV is basically a heat exchanger that allows you to replace stale air in your home with fresh air from the outside. It retains the temperature and humidity of the inside air and transfers it to the fresh incoming air. In the summer, the heat and humidity from the fresh outside air is "diffused" into the stale outgoing air. In the winter, the heat of the stale air going out is exchanged into the incoming fresh air.

    The unit features 2 variable speed blower motors (GE ECM), one for stale air out, and one for fresh air in. A third motor drives the energy transfer wheel/filter. I'll duct the unit into my existing HVAC (Trane XE 90) air return and interlock the two together so that the ERV only runs when the air handler blower is on.

    The 200DX ERV features a low voltage control PCB with the following connections:

    0-10VDC fan control input: Allows adjusting the air exchange with the outside air from 70-210 cfm. 1V = 70cfm, 10V = 210cfm. <1V fans off.

    Normally the unit runs in balanced mode, that is the in and out blowers run at the same speed. However, the out blower can be throttled back to create positive pressure in the house to prevent moisture from entering wall cavities, etc. A differential pressure transducer can be connected to the control PCB to retard the out blower motor to maintain neutral or slightly negative pressure.

    EconoCool: Bypass air exchanger to allow cool air into house when inside is calling for cooling. This eliminates the need to run the A/C and is very usefull during the night and mornings as long as the outside humidity is low.

    I would like to control my entire HVAC/ERV from my computer. I envision needing indoor and outdoor temp and humidity sensors and the ability supply a 0-10 VDC signal to the 200DX as well as provide a contact closure for the EconoCool feature based on the outside temp and humidity, in addition to the the normal closures for the HVAC (fan, heat and cool).

    As for the interface to the computer, I was thinking that the following items would do the trick:

    1 Midon MD2104 (TEMP08) rs-232 interface
    2 Midon MD3020E temp/humidity sensors
    1 Midon MD2083 4 channel relay board
    2 Motorola MPXA4115 pressure sensors (will need additional support electronics)

    I still miss something that will allow me to supply a 0-10VDC control voltage.

    But other than that, does this sounds like a doable design? Should I be looking at different hardware?

    I already have a computer mounted in a rack with a UPS and a backup generator controlling a 400 gallon reef tank, and it is very reliable, which of course is needed in an application that won't have a regular thermostat as a backup in case something goes wrong.

    DalSemi 1-wire digital potentiometer convert digital to analog (DS2890) 256 steps

    Alternate boards:


      Thanks Droopyear!

      Yes, the DS2890 looks like just the ticket. I wonder if anyone make a PCB board that will accept this device and a dual RJ-45 connector or if I'll have to make my own. It doesn't look like it will be that hard from looking at the data sheet.

      And I also discovered last night and their prices are a little better than Midon, not to mention the very compact rs232/usb to 1-wire interfaces they have. I also like their board coating option. I'll definately want that for my outside humidity/temp sensor.


        AAG has some nice packaging for their sensors. A humidity/temp module or a humidity probe. AAG products are OK, but support/RMA etc is quite poor.

        You can do your own software to interface the 1-wire, but if you want existing software then the xapmcs1Wire and a DS9097U(Serial)/DS9490(usb) is the only one I know that handles all the devices that you have in your candidate list. The 2890(D/A) and 2409(Hub) are not supported by most interfaces such as the Temp08.


          Thanks Michael. I took a look at the AAG website and their devices look nice. The pricing even seems little better than hobby-boards on some of the stuff.

          Ok, so I'll need the AAG DS9490R USB bridge to physically interface my various sensors and outputs to the HVAC system.

          I read some of the xAP newbie thread and your helpfull messages there. Guess I need to get the stuff on the "core shopping list" together not to meanting prepare for what looks to be quite a learning curve with all this xAP stuff.

          Ultimately, I was hoping to just needing to write simple logic statements and be able to monitor/plot inside and outside conditions to ensure that things were working as expected.

          You know, something like this:

          relay1 = "EconoCool"
          relay2 = "Furnace Fan"
          relay3 = "A/C compressor"
          relay4 = "Furnace Heat"
          dcvolt = "0-10VDC control for ERV blowers"
          if (outtemp < 70 and outhumi < 50) then relay1 = on else relay1 = off
          if intemp > 76 then (relay2 = on and dcvolt = 200)
          if intemp > 77 then (relay3 = on and relay1 = off)
          if intemp < 74 then (relay2 = off and relay3 off and dcvolt = 0)
          if intemp < 68 then (relay2 = on and relay4 = on and dcvolt = 200)
          if intemp > 70 then (relay2 = off and relay4 = off and dcvolt = 0)
          if (relay4 = on and inhumi >70) then dcvolt = 255

          The above is just a very rough example I came up with. I have no idea if those parameters will even be in the ballpark, but it gives an idea at least about what I'm trying to accomplish.


            The xAP learning curve only needs to be difficult if you are trying to develop new xAP applications. It is the same as the 1-Wire learning curve. Tough if you need to work directly with the protocol, but easy if all you want to do is use the applications that have been developed already.

            To run 1-wire in this environment you need:
            1. Microsoft Java VM
            2. OWAPI One Wire Drivers
            3. xapmcs1Wire

            To run xAP in this environment you need:
            1. mcsXap Homeseer plugin (or xAP Conduit)
            2. xapmcsHub (or hub from
            3. Recommend xAP Viewer from for diagnostics

            For analysis and control assistance the mcsTemperature plugin may be helpful. It gives you the type of triggering you are looking for as well as charting for analysis. If you want to roll your own then you should be able to do all your control with scripting under Homeseer.


              [QUOTE=Michael McSharry]AAG has some nice packaging for their sensors. A humidity/temp module or a humidity probe. AAG products are OK, but support/RMA etc is quite poor.

              i use only AAG devices and very best...

              "thinkig, thinking" - Winnie the pooh