Duct systems HRV-FCU in CONTAM-TRNSYS

[Rodrigo Mora]

Hello,

I have done several successful CONTAM-TRNSYS coupling simulations in the past. However, this time I have a tricky issue. I have a mechanical air distribution system in CONTAM with an air handler (simulated with a duct system and a fan, not the simple AHS), and a heat recovery ventilation "HRV" connected to the return air of the air handler (simulated as two fans in the duct system, supply fan at the air intake and exhaust fan at the air exhaust from the duct system).

I used ducts instead of a simple AHS for the air handler and the HRV because I need them connected at the same duct system to test the air distribution. Which I did already in CONTAM.

For the coupling in TRNSYS I would add room temperature control for the CONTAM air handler fan and a gas-based heating coil. For the CONTAM HRV fans, I would add heat recovery in TRNSYS (which I have done successfully in the past). My concern is how would TRNSYS respond to the duct coupled airflows between the air handler and the HRV in the duct system. Would TRNSYS not accept the intricate duct system and the coupled fans? Is there an easier alternative using the simplified AHS?    

By the way, the duct system operation with the Air handler and "HRV" fans works fine in CONTAM alone. I have tested thoroughly and it works fine. My concern is how TRNSYS will respond to these.

Thanks!

-Rodrigo

[William Dols]

Rodrigo,

I am not sure what TRNSYS components you are using to model your HVAC system.
Duct flows of CONTAM are available for data exchange, but you must manage the connectivity with TRNSYS yourself.
As you likely know, this must also be done with Simple AHS flows as well.
I would think that you would provide control of the CONTAM fan flows based on your TRNSYS HVAC System controls.

Perhaps you are already aware of the example TRNSYS-CONTAM case that implements a duct-based HRV system.
That case is available here: https://www.nist.gov/el/energy-and-environment-division-73200/nist-multizone-modeling/software/type98 in the cottage-dcv-t18-cx34-t9834.zip file.

Please feel free to reach out to me directly if you have any issues.

- Stuart

[Rodrigo Mora]

Thanks William!

I used the two papers in your link to implement my previous CONTAM-TRNSYS couplings. They worked very well. The challenge here is that my house has a recirculating air distribution system, which could be implemented with a Simple AHS, but the AHS has a heat recovery ventilator (HRV) implementing balanced ventilation using a fan to supply air to the return air duct of the AHS, and another fan to exhaust air from a corridor. Given the AHS-HRV connection, I had to implement a ducted AHS and make the "physical" ducting connection. It works fine in CONTAM. I have tested it with steady-state and transient weather. 

I plan to control the CONTAM AHS fan with a TRNSYS thermostat. In TRNSYS, I will also add a heating (with the gas furnace) and possibly cooling coil (for a scenario with a heat pump) to the AHS fluid/air, heating and cooling operation will be coupled with the AHS fan. I think this should work fine. The HRV will work continuously as required by the local code, but I will also leave room for CO2-based DCV (like with the cottage example). I think it should work, but I have not implemented this ducted coupling between systems, and I want to make sure I have my concepts right before I start. I think it should work, it should work because the airflows have been tested and calibrated in CONTAM, and the TRNSYS link will only provide means to control them based on temperatures. This is why I like the separation/coupling between airflows/contaminants and energy/temperature/humidity, because it gives me great flexibility to examine and calibrate airflows/contaminants separately before making the coupling. I have also used TRNFLOW in the past, and it does not give me the same flexibility.

I will keep you posted... 

Thanks a lot!

-Rodrigo  

[Rodrigo Mora]

Hi Stuart,

I ran into my first hurdle in CONTAM. I am controlling the HRV supply/exhaust fans based on CO2 (DCV), just like in the Cottage example provided by NIST. However, in my project I am setting the HRV at three speeds (min, med, max) depending on the indoor CO2 thresholds. The control logic works well according to the control report output (i.e. at low CO2 the control signal is 0.3, at mid CO2 the control signal is 0.5, and at high CO2 the signal is 1). I split the resulting signal result between the supply and exhaust fans (just like in the Cottage example). However, the HRV supply and exhaust fans are both stuck at 0.3 speed (low speed), regardless of the control signal.

Thanks,

-Rodrigo

On Fri, Jan 31, 2025 at 4:56 AM William Dols <willia...@nist.gov> wrote:

[Rodrigo Mora]

Hello,

I found the problem. I was running steady-state airflow simulations, and therefore the fan was operating at fixed initial conditions.

Thanks,

-Rodrigo