Robert Fassbender's blog

Solving Unmet hours - 7 Step Approach

Posted on: January 3, 2017

Nearly every energy modeler on the planet will ask at some point, “How do I solve unmet hours?”

Well, the rookie question would be “Which setting do I change to get rid of unmet hours?” or even better “Which button do I press to fix unmet hours?”

Sometimes a little naiveté is a good thing, but not when solving unmet hours. Experience matters and so does diligence. Being neurotic helps too. That’s where I come in.

In the past decade, I personally have taken unmet hours questions on over 1,000 files. There were only two times that I could not solve an unmet hours problem without “cheating” (such as tip #5 in our 6 Tips for Unmet Hours blog).

Of my two “failures”, one was a bug. The other instance was because the model was so messy that I couldn’t use my standard method. So, >99.9% effective. Here we go:

First, backup your file in it's exact state. Backup all your libraries too.

Always check these settings first

  • Are there driftpoints and if so, is there an Optimum Start schedule?
  • Is the supply air volume set? If so, is the supply air temperature?
  • Are the misc load/ventilation/infiltration schedules setup according to conventional methods (refer to trainings)?
  • Is anything scheduled unconventionally?

These 4 items often fix the problem and can be changed in 1 iteration because they follow best practices. However, if solving unmet hours only required four steps, it wouldn’t be such a big problem (caveat - “Overscheduling” is often a contributing problem that is hard to fix... custom schedules on things like coils, fans, and equipment)

To continue with my method:

What really ruins building efficiency

Posted on: May 13, 2016

You can design a ultra energy-efficient system. Maybe you designed an ultra energy-efficient building - a hard earned victory based on your knowledge of the first law of thermodynamics. Your energy model shows awesome results.

Now, the building is built and a fight against the Second law of thermodynamics begins. In case you forgot, the 2nd law basically states that “Everything tends to disorder”. Your ultra efficient building will not remain efficient without some help. And of course, the energy model is wrong.

Your building will trend towards inefficiency, and much faster than scheduled. This rapid decline isn’t the fault of your equipment selection, nor the fault of your control scheme, nor is it the fault of a poor installation. It is the chaos that happens inside a building; chaos brought by people. One or two complaints from an occupant, or a late night phone call, and your best laid plans are overridden. Your PID controller is turned into an On/off switch, conveniently left in the “On” position 24/7. Oh the humanity!

Personally, I’ve seen many buildings with overrides on both cooling and heating, both left on 24/7. Some of these buildings were only two years old.

What’s the solution? Well, first we should ask, what’s the problem? In the words of Homer Simpson, “The problem is communication, too much communication.” In many cases, they are legitimate complaints, but what really drives the chaos is the loudmouth complainer often referred to as a “Homer Simpson”.

6 tips for Reducing Unmet load hours

Posted on: March 20, 2015

Unmet Load Hours (aka “The Bane of the Completed Simulation”)     

What is an unmet load hour

Oddly, the definition of an unmet load hour is partially dependent on the software you are using, which may or may not allow you to define the throttling range (the acceptable +/- degrees where a space is deemed to be within its target setpoint). 

An unmet load hour occurs when the HVAC system lacks the capacity to keep the design setpoint within the throttling range for the duration of an hour. The other caveats are that the space must be conditioned, and in operating mode (occupied). 

Why do unmet load hours affect you? 

Unmet hours will stop a “completed model” from reaching completion. Some have said that they can quickly ruin your professional life (seriously).

If you have greater than 300 unmet load hours, your model will not comply with ASHRAE 90.1-2010 Appendix G. This means you can’t get your LEED points or achieve similar compliance unless you have a very good reason for the unmet hours. It's usually easier just to eliminate them. 

How can you lower unmet hours? 

There are an infinite number of inputs that can cause unmet hours. None of these are surefire fixes (except #5, which is cheating if it's the only one you use!), but here are 6 tips that should help in most simulations: 

Tip #1: Make thermal blocks 

7 Investments for Energy Modelers

Posted on: March 10, 2015

If you are reading this, there's the likelihood that you have wanted to smash your computer at one time or another. Now, lately, many of you may not be fond of investing in the stock market - so why not invest in your workstation? If you are fortunate enough to work for a company that can upgrade your equipment, this is what I have found to be beneficial. 

1) A large IPS monitor (& a 2nd monitor)

I'd recommend these ASUS monitors

I (like many of you) am very nearsighted and energy-modeling has further caused me a number of eye problems. I reduced this some time ago by getting a large IPS monitor, which paid for itself given the lowered eye doctor bills. 

In any case, I've found added benefits. I can avoid printing many documents (because I can read construction plans on my monitor - which saves a lot of money). In addition to a regular LCD monitor as a 2nd monitor, this allows me to read drawings and enter inputs simultaneously

2) A solid state drive

In my tests, a solid state drive (or SSD) speeds up calculations, but not substantially (make sure you enable TRIM, and disable auto-defrag!). However, the added benefit: we all know that our energy models crash, and always at the wrong time. With a solid state drive, your computer can be restarted in under 1 minute.

Chilled Beams vs High Performance VAV

Posted on: June 4, 2014

Hello Friends and simulators-

We get an awful lot of questions about modeling new systems, and rightly so. These often involve workarounds and many people do these workarounds differently. (Example, how do I model VRF in eQUEST?). 

What are some of these cool "new" systems:

  • Chilled Beams
  • Displacement Ventilation
  • Underfloor Air Distribution 

While all these systems have their own time and place, newer does not always mean better.
Before getting caught up in the hype of any new, flashy system, make sure that you don't disregard high performance technology in conventional systems (example high performance VAV). 

This is a great read, by an HVAC genius, John Murphy, PhD.

A building simulation can show wondrous results. When chilled beams were first implemented in TRACE 700, it was surprising to see that Active chilled beams saved little, or no energy over VAV systems. I dug into this myself and found that the much larger fan, when unloading as is typical in a VAV system uses less energy than the smaller fan that does not unload in an active chilled beam system. Who would've have guessed?! This is a perfect example of why energy simulation is needed. The results are often counter-intuitive.

Of course, there are places where chilled beams may be a better application, but a simple energy simulation may surprise you on the fan power consumed!

And By the way, TRACE 700 can model all of these flashy systems OOB (out of the box = no workarounds). So, if you would like to do some of these test runs, maybe give TRACE 700 a try.

Free New Course for Managers

Posted on: May 7, 2014


You probably always hear about needing better software, and that may be true, but remember that faster cars require better drivers. The software is not the limiting factor. Not even close.

I know you are busy, so to move straight to the point: we have put together a free tutorial to help you hire quality energy-modelers, or which energy-modelers you should retain (who deserves a raise?)

In a nutshell, the course covers:

  • The 5 factors to evaluate in an applicant
  • 20 example interview questions to help evaluate these factors (with answers)
  • Red Flags to watch out for
  • Ingredients to build an awesome team
Now, this course is for managers and employers only. I would personally like to extend to everyone, but let's face it: what good are example questions if everyone has the answers?
The course is complete but there are a few things I would like to add to it. Thus, please join the group if you are interested!
Again, to sign up, please join this linkedin group. (which can be used to verify your status as a manager). 

Not Conditioned But Not Unconditioned in 90.1?

Posted on: January 14, 2014

Last week, we received two incredibly similar inquiries related to the ruling in ASHRAE 90.1 from table G3.1.1a that “All conditioned spaces in the proposed design shall be simulated as being both heated and cooled even if no heating or cooling system is to be installed.”

Here is a sample of the question we received:

I have a space in the proposed that is heated only. It has a peak heating load of 12 Btuh/SF, but the baseline peak is 20 Btuh/SF. In this climate zone, heating is defined as conditioned when the peak load is greater than 15 Btuh/sf. Since the proposed is not conditioned and the baseline is conditioned, do I treat the space as unconditioned, semi-heated, or conditioned? If it is conditioned, how do I proceed?


That's a funny issue. To be clear, I'm assuming you are using 90.1-2007. In terms of heating for your climate zone, conditioned is defined as >15 Btu/h·ft2. Semi-heated is always defined as >3.4 Btu/h·ft2. By the way, semi-heated = a minuscule amount of heating. I have scarcely seen or heard of semi-heated outside climate zones 1, 2, or 3. Of course, the setpoint could largely determine that.

Since you have mentioned 15 Btuh/sf, that means your model is in climate zone 4 or 5.

In any case, the conditioned vs unconditioned should be based on the proposed value, which in your case, is not conditioned nor is it unconditioned. Therefore it is semi-heated. However, because of the climate zone, it is very possible that any small changes will move you into the “conditioned” definition.

You have two choices:

Experimenting with LED's

Posted on: January 9, 2014

Over a year ago, I decided to give LED’s a whirl and the LED's decided to give me a headache. I decided that I could not make a verdict on the purchase until a year had passed. It's been over a year, so here goes:

First thing, I did not install them for interior lighting, but for exterior night-time lighting only. I’m sure many of you are aware that LED’s are more popular for exterior lighting than they are indoors. In my opinion, exterior lighting is one of the best places to get LEED points because of the undisputed energy savings, plus LED’s can easily meet the lighting pollution reduction SSc8.

In any, case - why’d I update to outdoor LED’s? Naturally, I am energy conscious, but the main reason is because the incandescents were suffering very short lifespans and there was difficulty when changing bulbs in the outdoor fixture. I'd have said, "Hell with it", but the lighting is required by all residences in my neighborhood.The incandescents were averaging a lifespan of less than 1 month. I didn't know why at first but I finally realized that the wind was rattling the fixture, breaking the filaments on my “long-life” candelabra incandescents which were about $1 each.

The Perfect Storm to go Green?

Posted on: December 16, 2013

I’d like to ask you the reader, what do you think I mean by the word ‘green’ in the title of this blog. I'd guess that most of you thought of multiple facets of green, but primarily thought of energy.

In the past decade, most conversations you have likely had about anything 'green' have had a large emphasis on energy. In some cases, it was probably the only topic in the conversation; energy consumption has become the cultural catch-all for being green. (even though energy consumption is only a piece of the green pie!)

Why has 'saving energy' become synonymous with “green”? This may sound like a trivial question but to put it in perspective, consider that twenty some years ago, the phrase ‘green’ was synonymous with “Don’t be a litterbug” and not using CFC’s. To say the least, perceptions have changed, and we have reached a perfect storm for promoting energy-efficiency. In my opinion, this perfect storm is a result of a number of socio-economic factors. Here are the top 3 on my list:

Know Energy-modeling? Prove it!

Posted on: November 27, 2013

A lot of you are awesome energy-modelers. Now you can prove it. Recently, we sent out a survey which a number of you had participated in. Enough of you asked about Userpoints and how to get them and what they do. We did some brainstorming and decided to revamp userpoints and make the process as simple as possible. A few weeks ago, the top users were basically 3 people, and everyone else was near a tie, we decided to reset the board!

What do your Userpoints do for you?

  • Earn a reputation as a great modeler

Who has the most points?

  • Points = equal power 

(for example, allowing you to edit other users’ posts, or create your own blog entries). 

How do you get userpoints?

  • It’s simple: Post on the forum and answer forum questions.
  • Vote on the best forum topics and replies

When others vote for your post or your answer, you get 1 point. If they vote your answer down, you lose 1 point

So give it a try! You’ll be helping the entire community and earning acknowledgement for helping others.