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What ventilation system, E+ does and doesnt take into account for sizing calculation ?

asked 2018-11-15 06:42:42 -0500

Alexis's avatar

updated 2018-11-15 07:57:56 -0500

I am working on a project with DOAS with a heat recovery and a DX coil. Therefore, in E+, I have simulated this system with a DOAS templates, connected to a VRF.
I have found some unconsistent results for the capacity of the coil and I am not sure that the HX is taken into account for the size of the DOAS coil.
When I change the efficiency of the HX, nothing change for the DOAS cooling coil rate. However, for the node temperature and the energy, it seems to be taken into account because, The results are varying in the good way.

I have spent a lot of times to change some parameters, to understand the links between the inputs and outputs, to read some articles, some posts, in the purpose of understand my results.
So my question, what ventilation system/equipment, E+ does and doesnt take into account for sizing calculation ? Coil, exchanger, ...

DOAS + HX + coil is a very commun system, so if E+ can't simulate this system, what are your tricks or tips to simulate it ?
Thank you your help

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answered 2018-11-15 12:59:06 -0500

updated 2018-11-15 12:59:28 -0500

As you said, the full simulation models the HX as expected. Only the DOAS coil sizing neglects the HX.

From the Input Output Reference, "Input for Design Calculations and Component Autosizing, Overview":

The sizing calculations only recognize the presence of central heating and cooling coils, preheat and precool coils and reheat coils. These are assumed to deliver the various supply temperatures specified in the Sizing:System and Sizing:Zone objects. The impact of other components such as heat recovery, dehumidifiers, and pumps are not accounted for in the sizing calculations.

Repeating some suggestions in reply to helpdesk ticket 13109, if DOAS coil sizing is important for your study:

  1. If the DOAS coils are chilled water and hot water, you can adjust the design inlet conditions in the coil object to the expected conditions after the heat recovery.

  2. If the DOAS coils are not water coils, in the Sizing:System object, for the DOAS system, you could raise the cooling supply temperature and humidity ratio by the same amount that the heat exchanger lowers them so that the coil sees a smaller delta. Similarly, lower the values for the heating supply temperature and humidity. These won't be perfect, but should be reasonably close.

  3. Run the Sizing Period simulations and report the coil loads hourly or by timestep and use the peak to hard-size the coils.

This is an open new feature request.

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Thank you for the tips. "This is an open new feature request", it could be very useful and why not add an option to sum the CC of the DOAS coil to the VRF heat pump total cooling rate.

Alexis's avatar Alexis  ( 2018-11-22 01:21:34 -0500 )edit

I'm not sure I understand this comment. In Sizing:Zone there are fields for including the impact of DOAS when sizing other HVAC equipment serving that zone. See "Account for Dedicated Outdoor Air System` and related fields.

MJWitte's avatar MJWitte  ( 2018-11-23 09:41:15 -0500 )edit

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Asked: 2018-11-15 06:42:42 -0500

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Last updated: Nov 15 '18