[Bldg-sim] Lies, darn lies, and statistics

[Vikram Sami]

George Box coined that one I think

From: Bldg-sim <bldg-sim-bounces at lists.onebuilding.org> On Behalf Of Jim Dirkes via Bldg-sim
Sent: Tuesday, March 14, 2023 12:13 PM
To: chris.malcolm.yates at gmail.com
Cc: bldg-sim at onebuilding.org
Subject: Re: [Bldg-sim] Lies, darn lies, and statistics

I think Dru Crawley coined the phrase, "All models are wrong. Some are useful."

Chris, you highlighted an assortment of variables which are omnipresent, inconsistent and uncontrollable - so what, exactly, does your client expect? Is it a realistic expectation? For example, are they going to nail you to the wall when, inevitably, you are "wrong" next year?

I have not calibrated many models, but have been made more appreciative of all the uncontrollables by the ones I calibrated :(. All the statisticians know that there is always more than one solution which will result in a high R2 value or low CVRSME, so which is correct?

Rather than a calibrated model, lately I've been encouraging clients to consider one of the FDD platforms on top of their Building Automation System. Spending time and money to evaluate whether things are working properly makes more sense to me - it's "real life" vs a prediction. (Can't forget to mention thoughtful and thorough commissioning here; that's essential.)

ps, I love your thoughtful approach. You're setting a great example! One aspect of that is to reach out to the wider modeling community to gather input and feedback.

Jim Dirkes  1631 Acacia Drive NW Grand Rapids, MI 49504 -  616 450 8653
Coffee Conversation:
The "individual" is an impossible concept, conceived by the Enlightenment philosophers. It makes no sense to the Christian. In marriages, and families, in associations and friendships and religious orders, we are not individuals, but a communion of persons.

------- Original Message -------
On Tuesday, March 14th, 2023 at 2:10 PM, chris.malcolm.yates at gmail.com<mailto:chris.malcolm.yates at gmail.com> <chris.malcolm.yates at gmail.com<mailto:chris.malcolm.yates at gmail.com>> wrote:


I think I need to qualify this: informed by G14, but definitely not compliant with it! There is some allowance for repairing or “healing” data, but when the data has a lot of holes or modes/ category variables then forget it. This is my case, but the client still wants some kind of representative simulation.

Monthly models can be garbage. School holidays cut across months at different times, combined heat and power is popular which complicates gas usage especially when metering is limited… did the heat by-product of electricity generation go to the building, or was it rejected? They can work for heating in our temperate climate, but not for cooling.

Nevertheless, we need some kind of representative simulation model. We can’t make any ECM qualifying claims but we can do something useful. This is where these methods can give you a lot of insight before you start modelling.

I hadn’t tried the IMT previously. We tend to have limited our regression analysis to monthly “degree day” methods (your 2p model, I think). I plugged some project specific daily electricity data into the MVR example (multi variate regression) and it seemed to give decent CVRMSE (~2-3%) but low R2 (~0.7). However, it appeared to provide some insight on cooling usage (monthly 2p models are meaningless for this in the UK’s temperate climate).

I also made some 2p monthly models of gas. I thought these were good until I compared successive years. I guess this is were understanding a range of statistical indices is helpful.

Here’s the final rub, because the underlying data has so many inconsistencies that can only be made sense of with some regression models, it’s easier to “calibrate” the simulation model to the regression models than the original data. But I may use 2p monthly for gas, daily MVR for electric…

So I need to ask if I have wondered completely off-piste with this!

Chris

From: David Eldridge <dancingdavide at hotmail.com<mailto:dancingdavide at hotmail.com>>
Sent: Tuesday, March 14, 2023 12:53 PM
To: Jim Dirkes <jvdirkes2 at protonmail.com<mailto:jvdirkes2 at protonmail.com>>
Cc: chris.malcolm.yates at gmail.com<mailto:chris.malcolm.yates at gmail.com>; bldg-sim at onebuilding.org<mailto:bldg-sim at onebuilding.org>
Subject: Re: [Bldg-sim] Lies, darn lies, and statistics

Indirectly there probably isn’t a daily set of metrics in the Guideline since the simulation programs aren’t usually outputting daily results, but there’s no reason there couldn’t be one statistically.

You could make one if you had only daily utility data and had to aggregate the simulation results to daily totals, there isn’t a published target metric but you could still show that you calculated one and why you think it was a good or bad result.

DSE Mobile

On Mar 14, 2023, at 6:10 AM, Jim Dirkes via Bldg-sim <bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>> wrote:

Dear Chris,
Kudos for appreciating a gap in your understanding. (I'm in your camp)

On the other hand, there are SO many variables in building operation that, short of a highly instrumented (and carefully calibrated) building for everything from lights to people to plug loads to HVAC - calibration is a fiction (and I'm confident that no such building exists). Daily calibration is a complete fiction, perhaps even a deception. On top of that, a "calibrated" model is just a moment in time; everything going forward is guaranteed to be different than during the calibration time period.

I think of "calibration" as more like a sensitivity analysis - determine which variables matter more and which matter less. GenOpt works nicely for that purpose https://github.com/lbl-srg/GenOpt<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Flbl-srg%2FGenOpt&data=05%7C01%7Cvikram%40olsonkundig.com%7C23d28a6b405f47b5562808db24c09278%7Cd5b3df51a48046ba8f92ef77dd2c7d72%7C0%7C0%7C638144181738291281%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=dqFeAoOGreAjFSPjUPx7jYjnk6VDzoAgDtyGVo0z4DQ%3D&reserved=0>

Jim Dirkes  1631 Acacia Drive NW Grand Rapids, MI 49504 -  616 450 8653
Coffee Conversation:
The "individual" is an impossible concept, conceived by the Enlightenment philosophers. It makes no sense to the Christian. In marriages, and families, in associations and friendships and religious orders, we are not individuals, but a communion of persons.

------- Original Message -------
On Tuesday, March 14th, 2023 at 6:52 AM, Chris Yates via Bldg-sim <bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>> wrote:

Hi All

I do find ASHRAE Guideline 14 a little too hardcore for my basic understanding of statistics. I can plug any of the equations into Excel, but I’ve realised my statistics understanding is very limited! (I’m outed!)

We don’t actually have to work to G14 in the UK (probably good because my copy is a bit old). I finally realised I didn’t know enough after I’d been (lazily) using R2 in Excel on some monthly data. I thought that R2 > 0.9 was generally ok… yeah, it wasn’t.

So, are there any easy to understand resources available?

I’ve been messing around with the IMT as well. It’s been fun going back to DOS 😊. This got me into daily methods, which leads to my next question. Is there any reason why there isn’t a daily calibration option specified in G14?

Many thanks!

Chris Yates


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