HVAC issues

taharvey · Posts: 57

I have a few HVAC questions:

1. In the heating design tab, it does not show the solar gains in the graph, is it taking into account the solar gains for required HVAC requirements? If not will autosized HVAC be oversized?

2. If I set the HVAC model to simple, the simulation works, any time the inside temperature falls below the set point the HVAC mantains the temperature at the set point. If I set the model to compact the HVAC never comes on, the same as if I had no HVAC. How do I get compact to work?

3. It is not clear what the difference between simple vs. compact is (besides compact not working).

4. If the system autosizes the HVAC, where do I find what it was sized to? Instead of autosizing can a fix it to my own value?

5. Not all of the energyplus HVAC options are available like evaporative coolers, how do I access these?

6. If i edit the DesignBuilder input in IDF, can I then analyze the results back in DesignBuilder? how do i do this?

Andy Tindale · Posts: 1162 Location: Stroud

1. Solar gains are not included in the heating design calculations. This is because the peak winter design load takes place at night.

2. I can't say why compact HVAC is not working in your model, but if you send it in either as an attachment in this forum or directly by e-mail I will take a look.

3. The main difference between Compact and Simple HVAC systems is that Compact systems model the entire HVAC system in detail using ducts, heating and cooling coils, thermostats, boilers chillers etc. Whereas Simple HVAC systems are modelled using the EnergyPlus Purchased Air method which simply calculates heating and cooling loads. In both cases fuel consumption is calculated from the heating and cooling loads by applying coefficient of performance factors.

We will be expanding the documentation on HVAC systems over the next few weeks.

4. The heating and cooling capacities are stored with the Model Data on the HVAC tab at zone level. You can change these capacities by hand if you wish.

Any subsequent changes you make to heating and cooling capacity data will be overwritten if model options change. The Plant sizing building model option controls the way this works. You can access this data on the main tab in the model options dialog under the HVAC header. Search the on-line help for 'Autosize' for more information.

5. You can access all EnergyPlus HVAC options by exporting the model in IDF format and working with the resultant file in an external IDF editor.

6. You cannot currently import changes to IDF data back into DesignBuilder.

Regards
Andy

taharvey · Posts: 57

Andy,

Here is the file.

not only does compact mode not work, but the heater capacity is not showing up in the HVAC tab of the zone (though I can get that to work fine in other models).

Andy Tindale · Posts: 1162 Location: Stroud

Thanks for posting the file. Your Compact HVAC system is not operating as expected because the heating/cooling availability schedule is set using the air distribution operation data, which in your case is set to be on the outside the periods when heating and cooling is being demanded. Therefore availability and heating/cooling requirement schedules do not coincide and the system appears to be switched off.

This was not clear to you because you had 'air distribution' switched off. In version 1.0.2 and later heating/cooling availability is set to 'always on' when the air distribution is switched off and heating and cooling systems are switched on and off according to their respective operation schedules only.

Thanks for pointing this out.

Regards
Andy

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