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

Tue Mar 14 17:19:49 PDT 2023

Hello all,

Just a couple thoughts from a random passerby. It’s rare to see this email
group this active :p

Now please bear with my 2 cents:

One thing that always bother me when working on energy model calibration in
the past was: why was cross validation (CV) not used?

One fundamental technique in Machine Learning to avoid overfitting is
through cross validation. Fitting a complex first-principle model is
similar to training a complex black-box model: high degree of freedom,
risks of overfitting. CV can be adopted to avoid incorrect local minima
during model training. There are multiple CV approaches for timeseries
model training.

And regarding predicting peak loads, etc. When training a model, the loss
function (equation that describes model accuracy) dictates how you want the
model to behave. Usually RMSE is used but you can customize it to make the
model behave in a certain way better. For example, something like a
compound loss function that combines prediction errors from both overall
predictions as well as peak prediction. You can adjust the weight for each
component to dictate which part is more important than another.

Thanks,
Shawn Shi

On Tue, Mar 14, 2023 at 7:41 PM Dru Crawley via Bldg-sim <
bldg-sim at lists.onebuilding.org> wrote:

> Yep, not me. But I use it a lot.
>
> On Tue, Mar 14, 2023, 4:19 PM Vikram Sami via Bldg-sim <
> bldg-sim at lists.onebuilding.org> wrote:
>
>> 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
>> <https://www.google.com/maps/search/1631+Acacia+Drive+NW+Grand+Rapids,+MI+49504?entry=gmail&source=g>
>> -  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 <
>> 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>
>> *Sent:* Tuesday, March 14, 2023 12:53 PM
>> *To:* Jim Dirkes <jvdirkes2 at protonmail.com>
>> *Cc:* chris.malcolm.yates at gmail.com; 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> 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
>> <https://www.google.com/maps/search/1631+Acacia+Drive+NW+Grand+Rapids,+MI+49504?entry=gmail&source=g>
>> -  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> 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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