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Author Topic: Air Handling Unit interval Fan control  (Read 2069 times)

Offline petclaud

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Air Handling Unit interval Fan control
« on: October 30, 2016, 06:52:18 am »
Hello all. Posted the question below initially in the HVAC topic, but moved to here as advised. Maybe somebody has a good idea.

The following I try to achieve: I have an Air Handling Unit with a heating coil inside it. The fan of the AHU is a always on. A normal (non-z-wave) room thermostat switches on the heating boiler supplying then warm water to the heating coil in the AHU.

My idea is switch the AHU fan on/off via an interval timer to save energy. The fan should be always on when the supply temperature to the heating coil is above a certain set temperature (SP). When the temperature is below the set temperature (SP), the interval timer should do its work (switching the fan On and Off). The following conditions are applicable:


No.    Supply Tem   Function   Interval timer   Fan
1   >SP               OR           True                   On
2   > SP              OR           False                 On
3   =< SP            OR           True                   On
4   =< SP            OR           False                 Off


I have installed the App PLEG and PLC and used the logical OR function with a temperature sensor point and an interval timer, but somehow it does not work.

The logic, interval timer settings and logic details are here:

(http://i65.tinypic.com/mvnd01.jpg)
(http://i67.tinypic.com/n2zuw2.jpg)
(http://i66.tinypic.com/2wprseb.jpg)

t1TemperatuurSensor is set to give a True when the temperature goes above a set temperature.
s1IntervalTimer is set as a regular timer (in the picture it is set as an interval timer 1:01 on for testing purposes, but the final setting will be something like 20 mins On and 20 mins Off)

In the logic block c1TempORTimer is an OR function with the variables t1TemperatuurSensor and s1IntervalTimer. On this basis I switch the ePlug_Schakelaar On or Off (set 1 or set 0)


Somehow this does not work. The interval timer is very irregular and I cannot find any pattern or logical reason why this does not work.  :-\

Materials in use:
- Vera Plus
- Fibaro Universal binary sensor with temperature sensor
- Smartplug


Anybody any idea...?

Offline Mike Yeager

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Re: Air Handling Unit interval Fan control
« Reply #1 on: October 30, 2016, 07:46:23 pm »
Why not simply add a relay that turns the fan on when the thermostat says heating is needed? I don't see a need for the interval application but I can probably find reasons for it other than the obvious one of not running the fan all the time. Do you have A/C as well in this system?

Offline petclaud

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Re: Air Handling Unit interval Fan control
« Reply #2 on: October 31, 2016, 12:48:09 pm »
Hi Mike, thx for your message. The need to turn the fan on/off is to circulate the air trough my house. It is an Heating and Ventilation system with ducts throughout my house. In order to circulate (and refresh) the air I want to switch it on and off. Switching the fan off, is to save energy. Later, I might add that based on a scene (ie being home) that the fan interval is different than when I am away.

Offline Mike Yeager

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Re: Air Handling Unit interval Fan control
« Reply #3 on: November 01, 2016, 05:55:57 pm »
Ok, here's what I'm doing. I have an Ecobee3 installed so I'm doing most of it through the thermostat. I'm running my heating and cooling pretty much automatically, but the fan will run a minimum of 10 minutes every hour regardless of everything else. For example, if the temp is set at 75 at night, and the room cools to 72 due to outside temperature, the fan will circulate the air even though the A/C will never come on since my heat is set at 60. Same could be done with a standard relay (24v AC most likely) and a Z-Wave relay in parallel to it. What thermostat are you currently using? The reason I ask is that, unless it's some funky thermostat, it should be capable of controlling the fan on it's own. If it is, then half the work is already done. Can you provide a basic idea of how it's wired now? I'm assuming that when the thermostat calls for heat, it energizes a solenoid (or powers a pump) to allow the water to circulate. This is very doable and we can get you the control you want, it's just going to take a little time to figure out what we have first...

Offline RichardTSchaefer

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Re: Air Handling Unit interval Fan control
« Reply #4 on: November 02, 2016, 12:26:20 pm »
Mike,
   The SmartPlug is essentially a relay.

   I actually do much the same thing with my Forced Air HVAC system. But I only have to turn the FAN from Auto to On when needed.


Offline Mike Yeager

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Re: Air Handling Unit interval Fan control
« Reply #5 on: November 03, 2016, 02:17:37 pm »
I figured the Smartplug was basically a relay, but the fans in heating and cooling systems are usually 220v. I'm trying to determine if his thermostat is capable of handling the fan on it's own for heating. If it is, just need to parallel in another relay to cut it on and off on his demand.

Offline petclaud

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Re: Air Handling Unit interval Fan control
« Reply #6 on: November 04, 2016, 05:19:54 pm »
Mike, Richard,

Than you both for your support. My question / problem is solved and it works fine now (answered by Richard in my initial post in the HVAC section - sorry maybe I should have closed it here).
Just FYI, I will try to explain the setup of what  I have:

I have an Air Handling unit. It is basically a box with a fan and a heating coil - nothing more, nothing less. Airducts are connected to the box, circulating the air throughout my house (all the rooms). The fan of this box is 24/7 on. Basically it is a closed system; blowing air into the rooms via ducts and extracting via ducts and recirculate the air. Via another system, a certain amount of fresh air is mixed with the circulated air in order to have / maintain a healthy indoor climate. A Central Heater - maybe you would call it a hot water boiler - is connected via tubes to the heating coil. A programmable thermostat (different times, temperatures, etc.) switches the Central Heater on/off if the temperature drops below te setpoint in the main living room.

I do not have the intention to replace the thermostat, since this works flawless; I only want to save some energy, hence the idea to switch on/off the fan if there is no heating demand.
Hence I measure now the temperature of the supply tube of the heating coil and if this is above a set temperature - there is a heating demand - the fan should stay on, otherwise the fan should be switched on/off via a set interval. I need the fan to run now and then, in order to circulate the air in rooms (including fresh air) to maintain a healthy climate. Indeed a smartplug is used to switch on/off the fan.

So with Richard's help, I got this working now (I misunderstood the principle/setting of the interval timer - the logic was already correct).
Thx again for the help!!



« Last Edit: November 04, 2016, 05:23:42 pm by petclaud »

Offline Mike Yeager

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Re: Air Handling Unit interval Fan control
« Reply #7 on: November 04, 2016, 07:41:14 pm »
Glad you got it working, I was just trying to save you a device or two in the process. I wasn't even thinking of replacing your thermostat... As long as it's working!!!

Offline petclaud

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Re: Air Handling Unit interval Fan control
« Reply #8 on: November 05, 2016, 01:51:09 am »
Thx Mike,
Cheers.