Bob Fassbender's blog

When R-50 is worse than R-25

Posted on: March 12, 2015

If you are reading this, it is likely you clicked a link from our email series explaining energy modeling and it's benefits. Specifically, the email "How does Energy modeling save energy?"

In this case, R-50 insulation used more energy than R-25 in a building in Denver, Colorado.

The main issue was that the R-25 building did not need heating or cooling for most hours when the outdoor air temperature was between 50 and 67 degrees. The building with the extra insulation, on the other hand, did not need heating or cooling between 50 and 58 degrees (the sweet spot was half the size when adding the extra insulation).

In this example, R-50 used MORE energy than R-25. Here's why:

The extra insulation did save energy during many hours of the year, especially when the temperature was below 30 degrees fahrenheit.

HOWEVER, the local climate had hundreds of hours where the temperature was between 58 and 67. This meant that the cooling equipment had to run for extra hours BECAUSE of the extra insulation was effectively trapping heat inside the building during those hours.

I thought of a very simple test. I magically moved the building to a cold climate (I live in a cold climate and I know how important insulation is).To “magically” move a building in an energy model, you just need to switch the weather file. I chose the coldest place I could find within my weather files and that was International Falls, Minnesota.

I ran the simulation and showed a substantial savings for the R-50 insulation, as one would expect in a really cold climate.

What is Energy-modeling?

Posted on: September 8, 2014

It is very difficult to answer the question "What is Energy-modeling" in as few words as possible. Here is my latest attempt that will soon be edited and published in, Architectural Drafting and Design, published by Cengage, 7th Edition.

Definition of Energy Modeling

Energy modeling, short for Building energy modeling (often abbreviated as BEM), is the computer simulation of a building used to determine or estimate building energy usage. A virtual building is created in a software package, the building components are entered, and the building is simulated over the duration of 1 year using a weather file.

The components entered into the simulation are numerous and thus most energy models allow for some simplification. For instance, the lighting may be simplified into watts per square foot, as opposed to determining the exact wattage for each and every room. Other example inputs include: fan horsepowers, pump horsepowers, heating and air conditioning type and efficiency, receptacle power, people, and outdoor air requirements. Of these inputs, the heating and air conditioning inputs often require the most knowledge because of the plethora of options available on the market.

5 Psychrometric Tips to Keep You from Going Psycho

Posted on: July 15, 2014

I remember learning Psychrometrics in college. It was in one of my early chemical engineering classes and was really just a footnote to our main syllabus. The Professor was walking through it on the chalkboard, and explaining this and that; I thought that it seemed rather intuitive and unimportant to my career path (the irony!). I stopped taking notes and decided to sit back and try to reason through it. Somewhere mid-lesson I must’ve started daydreaming because suddenly the bell rang, and class was dismissed. I didn’t look further into it.

A few weeks later, we had our midterm. I had studied everything in my notes. So naturally, about 90% of the mid-term was based on psychrometrics. I thought, “no big deal, I remember enough of the lesson to do this”. Then, I looked at the psychrometric chart provided with the exam and it was unlabeled. I tensed up and kept snapping off the tip of my pencil. I decided to take ten minutes and think about the weather. Living in Wisconsin, I’d experienced almost every point on the psychrometric chart in the past 6 months, and I was able to deduce the labels on the chart. I got an A/B on the test, and thought, “Whew - at least I will never have to think about psychrometrics again”.

Fast forward 3 years, and I’m in Trane’s Graduate Training program, taking test after test… solving psychrometrics, with a very sharp pencil and plastic triangles. Six months later, I’m working in the support center, and a large percent of support calls require a detailed knowledge of pyschrometrics - especially calls related to HVAC nuances and building simulation. At that point, my relatively simple knowledge of psychrometrics helped me solve a number of convoluted problems.

LEED Fan Power- Step by Step

Posted on: February 10, 2014


USGBC is asking me for a manual calculation on fan power. Can you walk me through how you calculate the fan power for a VAV system for LEED?


It’s a pretty straightforward process. However, it does require some bouncing around in ASHRAE 90.1 and that can lead to confusion, so after this walk-through you might simply prefer to use our fan calculator. One of the most complicated parts of the calculation is determining the filter credit. But remember that you should only apply the fan credit if ALL the supply air is filtered. (The workaround is discussed in the next segment)

It's best to use an example: Let’s say you have a sound attenuation device on your full supply air of 10,000 cfm and you have a MERV 13 filter on your 2,500 cfm of ventilation air (and only on your ventilation air).

The fan credit (from 90.1 TABLE is .15” for the sound attenuation device and .9” for a MERV 13-15 filter.

From the footnotes of TABLE, we see that the credit only applies to the cfm that the air goes through in the filter or device, so the equation for A (in the footnotes) is:

A = sum of (PD× CFMD/4131).

In this case that yields:

A = .9*2500/4131 + .15*10,000/4131 = .908 hp

Then, from Table G3.1.2.9 for variable air volume systems you use:

BHP = CFMs*0.0013 + A

Thus, you have

BHP = .0013*10,000+A = .0013*10,000+.908 = 13.908 bhp

You then have to move to the KW, which is calculated from G3.1.2.9. Since it is VAV, you use the equation for systems 3-8, which is

TOTAL system fan power in watts = bhp*746/efficiency

KW = bhp*746/1000/efficiency = bhp*.746/efficiency

Modeling Heat Pumps in TRACE 700

Posted on: February 22, 2013

So you want to model a heat pump in TRACE 700? And in reality, you have no backup heat... Or maybe you have backup heating, but you know it will never operate because you have an enormous geothermal well.

Regardless, of the scenario, there's a few key features to modeling heat pumps in TRACE 700. (There's probably several dozen main components - but lets look at a few tips).

Keys to Modeling a heat pump in TRACE 700:

1) Create a backup heating plant (this should actually be your first step). You should technically have 1 backup heat plant for each cooling plant (even if in reality - this never operates). Do not set the capacity to zero - regardless of what you have heard in the past. See, if you set it to zero, you'll have no good way to troubleshoot later.

2) Create your cooling plant as a heat pump plant. The key here is to set the heat source to the corresponding backup heat plant. Typically, keep the 'reject heat condenser heat to' the default field. 

3) For the cooling plant, the cooling capacity and efficiency are important as normal, but the "heat recovery" capacity is actually the "heating mode" capacity, as well as the efficiency. The default value of 14.4 mbh/ton is actually a pretty good number, though it's often best to put in the exact capacity.

The rest depends on weather or not it's an air to air heat pump, a water source heat pump, or a VRF heat pump, and this topic could get rather lengthy.

The key part to understand is what happens with the coils:

Your system will have heating coils and cooling coils. The heating coils MUST be assigned to the backup heat source, and the cooling coils must be assigned to the heat pump cooling plant.

TRACE 700 users must know these 7 things

Posted on: January 23, 2013

TRACE 700 is unique Building simulation software - Especially since it does both load calculations and energy modeling.  There's a lot of people that use TRACE 700 to do a lot of different things: Load Design, LEED models, Life Cycle payback, just to name a few. 

Did you know that TRACE 700 is over 2 million lines of Code? TRACE 700 is incredibly complex and has computational power that far exceeds anything you can do on a spreadsheet!

So, depending on your job title -  you may or may not use certain features of the program. For example, maybe you need to interface with GLHE pro for sizing Geothermal wells (TRACE 700 can do this, and more!), but maybe you don't

In my travels, training at various places, I've found there are 7 basic things that all TRACE 700 users should know (but often don't). If you run into someone who claims to know TRACE, but doesn't know these 7 things - chances are they don't have as much experience with the program as they may claim!

7 - Limit file names to 15 Characters

If you've never heard of the 15 character limit, it's likely that you have never heard of archiving files (#5). You can't archive a file with a name over 15 characters. There's a long explanation to how important this is. But let's just say that long names (over 15 characters) lead to buggy files!

6 - Sort lists Alphanumerically

Did you know you can sort lists alphabetically in TRACE 700? So, when you click on your room dropdown menu - rooms are easy to find. You can do this by going to the options menu at the top of the screen and selecting "sort lists".

5 - What an Archive file is...

Approved LEED simulation software packages

Posted on: January 9, 2013

I've never attempted a list of LEED approved software for LEED EAc1, and EAp2. I am sorry to omit anyone, but it's a common question.

First - There are a lot of software packages that can be used that are not mentioned explicitly (see "Other" in the list below)

Second - To give a simple answer to the question, LEEDonline does in fact have a list of common software programs (so it can tell you what reports to upload). Though it has been pointed out that LEED does not actually approve software, the actual software approval process is fairly complex, so the purpose here is to keep it simple.

List of approved LEED software

(Bold indicates it is mentioned within the LEEDonline v3 EAp2 forms)

  • DOE2
  • eQUEST
  • Visual DOE
  • EnergyPlus
  • EnergyPro
  • HAP (Carrier HAP)
  • TRACE 700 (Trane TRACE)
  • OTHER (see requirements of Appendix G, Section G2)
  • BLAST (not mentioned within the LEED form, but listed in 90.1 section G2)
  •  IES (Integrated environmental solutions, listed in LEED Advanced energy modeling)

Please comment with other software that you have used for LEED certification for EAc1

Convert EnergyPlus weather to eQUEST

Posted on: January 8, 2013

As energy modeling grows worldwide, the demand for international weather has grown. eQUEST - being so popular, has a lot of weather locations, but a modeler often needs more.

A lot of you want to edit the weather, or create your own weather files and this can be done with our handy weather editor (so long as you have nearby area to start from). But, a lot of you (eQUEST/DOE2 users) need to convert your .epw weather to .bin data - which we can do here

Energyplus has a large set of international weather, but it must be converted to .BIN format. This process is easy, but there is a slight glitch in the initial install. Check out this video to see how to convert and use energyplus weather files (epw files) in eQUEST.

The links mentioned in the video are listed below the video (don't forget to go fullscreen, and select HD)

Get the weather converter

Energyplus weather locations 

A note on file paths

Also, please note that this was done with Windows 7 (we deliberately skipped file paths because they can be different on different operating systems, and custom installs)

Typically, the weather folder is located in C:\Users\Public\Documents\eQUEST 3-64 Data

Modeling framed walls - steel studs/wood studs

Posted on: January 3, 2013

Okay, so you've got your building geometry setup, and now you are moving on to replacing the default construction types with your actual construction types (using actual roof, wall, window details).

You quickly notice that your software package does not have an input for stud type, nor any sort of inputs relating to joists/studs (this is true of many software packages).

So How do you model joist/framed walls or roofs (steel, wood, or otherwise)?

The most common answer is found in ASHRAE Standard 90.1, Appendix A. 

Since many modeling programs can only models layers in 2 dimensions, the standard provides guidlines for this for roofs, walls and more. We will focus on an example of a Steel-Frame Wall.

Chiefly, you need to know the following:

  • Stud distance (16 on center/24 on center)
  • Depth of joist
  • R-value of continuous insulation

Knowing these numbers, you can lookup Table A3.3 in ASHRAE std 90.1 (for steel-frame walls).

From the table, you can find the overall U-factor of the assembly (and your modeling program should have an input for this!).

WARNING: it is not always best practice to simply model the U-value

The U-value is important, but the mass of the materials is typically important too. Thus, it is a good idea to model layers that yield a similar U-value to the one in Table A3.3, and that also have a similar thermal mass. Given the example of steel joist walls, an example would be to have the following layers:

  • Exterior layer (sometimes Air films need to be included)
  • Stucco
  • Gypsum board
  • Insulation
  • Gypsum board

Energy Modeling on the Rise - Headlines ASHRAE

Posted on: December 19, 2012

Many of you ask about trends in energy-modeling, or if energy-modeling is on the rise. For those who ask, you probably already know, and are just looking for confirmation. Yes, Energy-modeling is becoming more and more important for several reasons. You can see these reasons below, but first, let's validate the claim that energy-modeling is on the rise.

Proof of this, is that the latest ASHRAE Journal headlined "Energy-Modeling - Making Good Assumptions", in a very well written article on the topic. (Also, thanks for mentioning!).

When ASHRAE does something, everybody else follows. Sure, we hear a lot about USGBC, GBCI, and LEED, and so on... BUT none of those organizations operate without ASHRAE (since they all cite ASHRAE literature). In actuality, Energy-modeling would not exist as we know it without ASHRAE, (they developed many of the algorithms and continue to do so).

Let's not forget ASHRAE President 2010-2011 (the late Lynn Bellenger - God bless her), had the motto of "Modeling a sustainable world", further indicating the importance of modeling to ASHRAE. (Especially since Lynn was considered perhaps one of the most important presidents of ASHRAE, being the first female president since the organization began 116 years earlier!). In fact, AIA (another huge organization) also jumped on board with their publication of an Energy-modeling design guide earlier this year.

Finally, consider that Energy-modeling headlined the latest article in the December 2012 ASHRAE Journal, it is obvious that energy-modeling remains important to ASHRAE, and the industry at large.