Heating in MMV lower than in HVAC

[kamilakrych]

Some time ago, @nheeren has noticed that the MMV variants of some archetypes display not only lower cooling, but also heating:

Problem is two-fold, and I managed to fix it, but I'd like discuss how we should proceed with Problem 2.

Problem 1: decision tree It took me ages to find this mistake. Based on the decision tree, when the zone indoor temperature was between the heating and cooling setpoint, both the HVAC and the NV was off. That's wrong, HVAC should be on. Probably E+ uses some optimizing algorithm, which can turn on the HVAC even before the temperature reaches the setpoint. This was happening in the HVAC variant, but not in the MMV variant. A painful way to learn about it... I need to update the MMV documentation.

Problem 2: infiltration In the MMV variant, natural ventilation is modeled using using AirflowNetwork (AFN) objects that simulate air flow through the building. This means that all types of airflow must be modelled using AFN objects, including infiltration. Consequently, the HVAC and MMV variants simulate infiltration differently, which changes the heating and cooling demand. In other words, we're comparing oranges and apples.

In order to compare apples to apples, I suggest we should use AFN objects as default in the HVAC variant of all archetypes. This increases the simulation time around 2-4 times, depending on the archetype. Should we do it? If yes, how: should I substitute the archetype IDF files or just perform IDF file manipulation before each run?

I have tested this solution on all archetypes and the result is as below. Heating is comparable for the AFN variant (= HVAC variant with infiltration modeled as AFN objects) and the MMV variant, while cooling is slightly lower for the MMV variant.

Commits with the fix will follow soon. But the main commit depends on how we approach Problem 2.

[nheeren]

Problem 2: infiltration In the MMV variant, natural ventilation is modeled using using AirflowNetwork (AFN) objects that simulate air flow through the building. This means that all types of airflow must be modelled using AFN objects, including infiltration. Consequently, the HVAC and MMV variants simulate infiltration differently, which changes the heating and cooling demand. In other words, we're comparing oranges and apples.

@kamilitsa That is some impressive detective work! Thank you!!

I'd prefer we change all (maybe not the hospital though ;) archetypes to AFN for reasons of consistency. Do you or @shnkn see strong arguments against this move?

[shnkn]

great work @kamilitsa!

In my archetypes, I also use AFN only, so there is nothing against it from my side @nheeren :)

[kamilakrych]

Ok, thanks for feedback :smile: So I'm going to proceed with the commits then. I plan to update all the archetypes to use AFN by default and to include the AFN converter as a part of BuildME. Even if we don't need to use the converter on a regular basis, it could be useful for potential future archetypes (and for other BuildME users).

@nheeren Why not hospital though? I actually managed to make this archetype work now, with the new algorithm :) In our last meeting I told you it didn't work, but it does not. Although the cooling savings are not that big, because most zones are not MMV-compatible (they don't have windows).

[nheeren]

Awesome!

@nheeren Why not hospital though? I actually managed to make this archetype work now, with the new algorithm :) In our last meeting I told you it didn't work, but it does not. Although the cooling savings are not that big, because most zones are not MMV-compatible (they don't have windows).

As you like. But it already takes ages to simulate.

[kamilakrych]

@nheeren Why not hospital though? I actually managed to make this archetype work now, with the new algorithm :) In our last meeting I told you it didn't work, but it does not. Although the cooling savings are not that big, because most zones are not MMV-compatible (they don't have windows).

As you like. But it already takes ages to simulate.

Not really! For me, hospital with the conventional HVAC takes 1.5 min and with the HVAC with AFN takes 3 min. Below you can see a summary of the simulation times on my laptop (which is not particularly powerful).

No.	Name	HVAC	AFN	MMV
1	MFH	02:41	08:37	12:04
2	OfficeMedium	00:39	02:34	03:08
3	RetailStandalone	00:13	01:36	02:17
4	RetailStripmall	00:23	02:43	03:20
5	RT	01:04	06:03	08:20
6	SchoolPrimary	01:06	06:57	12:04
7	SchoolSecondary	02:31	16:24	49:14
8	SFH	00:29	01:19	01:29
9	Hospital	01:29	03:11	07:57
10	HotelLarge	00:39	03:17	09:31

So, as you can see, what takes ages to simulate is SchoolSecondary...

I would argue it's good to have the same approach to all archetypes, but I want to leave the last word to you. Otherwise, how would I proceed, should I prompt a message saying that archetype X is not available in the MMV version and skip the simulation?

[nheeren]

Not really! For me, hospital with the conventional HVAC takes 1.5 min and with the HVAC with AFN takes 3 min. Below you can see a summary of the simulation times on my laptop (which is not particularly powerful). No. Name HVAC AFN MMV 1 MFH 02:41 08:37 12:04 2 OfficeMedium 00:39 02:34 03:08 3 RetailStandalone 00:13 01:36 02:17 4 RetailStripmall 00:23 02:43 03:20 5 RT 01:04 06:03 08:20 6 SchoolPrimary 01:06 06:57 12:04 7 SchoolSecondary 02:31 16:24 49:14 8 SFH 00:29 01:19 01:29 9 Hospital 01:29 03:11 07:57 10 HotelLarge 00:39 03:17 09:31

Thorough as always! Thank you! In our last check-in we discussed that window ventilation in a hospital makes little sense. So I don't fully see the point. I suggest we leave the old HVAC archetypes available for reference. Ie have two files, one Hospital.idf and one Hospital_HVAC.idf. Do you think that makes sense?

[kamilakrych]

The old archetypes are available under the AFN Converter tool. I'm closing this issue.