Putting Passive House to the Test! Pt 31 - Annual Heating Demand & the Monthly Method

Technically, today I managed to make the Bunkhouse meet the Heating Load requirement for Space Heating (and I almost met the Annual Heating Demand requirement as well!)  I say technically because it was never the plan to spend $100k to build a $10k trailer.  However, since it was all on paper, I decided to see what it would take.  The Annual Heating Demand and Monthly Method worksheets gave me some visual feedback to help me decide what needed tweaking to get to my goal. 

Let’s start by understanding what the Annual Heating Demand and Monthly Method worksheets are for.  These worksheets are both designed to meet the EN 13790 method of calculating the heating demand for your project.  The PHPP manual states that both methods give similar results with the Monthly method being more accurate, but the Annual method easier to understand.  I found I used the information on both worksheets to help me understand the project.  Only one can be chosen as the basis of the heating demand calculation for the PHPP (and this is done on the Verification worksheet), but you can still look at the graphs on both the Annual Heating Demand and Monthly method worksheets to help you understand what is going on. 

Here are the charts I ended up with after I threw lots of money at the project and met the Heating Load requirement: 

You will see that the Annual Heating Demand chart shows where I can expect to see the heating gains and losses and at what percent.  This helped me decide between more insulation and changing window sizes.  The Monthly Method chart showed me how much free heat I could expect each month and also showed me when I could expect overheating.  The Blue line on that worksheet shows me what my losses are for each month, but not where specifically I am losing the most heat.  That’s why I used both charts.  By looking at both charts I could see how changing the window sizes would affect both overheating and heating.  I could see how adding insulation affected the heating demand on both charts as well, but the Annual Heating demand sheet broke down the difference between the losses from the walls and those from the ceiling/floor areas so I was able to target where the additional insulation would do the most good.

Because the PHPP mentions that the Monthly Method was harder to understand I decided to see if changing the chart slightly would help me see it better and I found that I like it this way.  (I didn't change it in the PHPP, I just made one by hand).  I put the Solar and Internal Heat Gains on the bottom of the chart (in yellow) since I knew I automatically had those.  Then I placed the Heat Demand (in red) above those to show what I would need to make up for the additional losses that I could expect (the blue line).  I also added an area that shows overheating more clearly for the summer months (yellow with red cross hatch).  June and September are actually special cases with free heat, heat needed, and over heating all in the same month.  By color coding these charts and studying them you can really get an understanding of your project.

So, technically I was able to get past the first hurdle and meet the Heating Load requirement on paper.  But what does the Bunkhouse look like overall and close up?  Up next I will draw the bunkhouse to scale with the window sizes that worked and see if I can find out exactly how many gold bricks I would need for the vacuum panel insulation.  I’ll also pull together some PH nerd numbers for all the folks who are wondering about R values and TFA.

Up Next – Bunkhouse Nerd Numbers.

Putting Passive House to the Test! Pt. 30 - Ground Control to Major Tom

As I began to write this week’s blog entry I realized that I was a total space cadet and had forgotten one important calculation to do for this project – the Ground worksheet.  This worksheet can be skipped in some cases and a default value is then used by the PHPP, but since this is a rather unique project when it comes to considering the Ground aspect, I wanted to make sure I filled in that worksheet.

The closest ground category the PHPP has to “Cork House with Metal Exoskeleton Built On Top of a Metal Trailer” is “Suspended Floor”, so I will work with that.  At this point I am flying blind as far as what would actually be certified by PHI for this, so this blog post will serve as a learning tool for me and anyone else who isn’t sure what it is they know or don’t know about a PHPP worksheet. 

This I know - PHI is busy.  Incredibly busy.  I can’t email them and say “I’ve got a weird project and it doesn’t fit your PHPP, what do I do?”  I need to understand what the worksheet is looking for and why.  Then I need to figure out how my project fits into that format and how to get the information I need to fill in the blanks.  When I have done all that and STILL have a question… I ask another CPHC.  Seriously.  

We need to interact with the folks in our community that are working the very same problems we are.  As we get to know each other, our strengths shine and we find those who can help us or they find us so we can help them.  That’s what I did with my window Psi G problem.  When I heard that my go-to window gal, Bronwyn was going to talk to PHI about the very same issue, I didn’t bother them.  She’ll figure it out, I’ll learn from her, y’all will hear from me. 

So, let’s look at the Ground Worksheet and see what I know and where I get stuck.  The first thing the PHPP is looking for is the Heat Conductivity and Heat Capacity of the soil.  My first thought was that it would be irrelevant since my project does not technically sit on the soil.  But, using my earlier statement, I need to find out what the worksheet is looking for and why.  The PHPP tells me that “The ground surface temperature rises and falls over time as a sine wave that has an amplitude approximately half the difference between the maximum and minimum monthly average ambient temperatures.” [PHPP 2012 pg 60]  In other words the air could fluctuate from an average 30degF at night to an average 50degF during the day for the month of April – a fluctuation of 20 deg on average, but the ground temps may only fluctuate about 10 deg on average for that area during the same period.  Tying your building to the ground is better than putting it on top of a steel trailer.  However, that steel trailer will sit on the ground and perhaps the ground will transfer heat to the trailer through radiation so I still need to consider this information in my PHPP.  The kind of soil I have happens to be the default, so that is already filled in for me.  Check the PHPP manual for the soil values that your project has. 

Under “Building Data” the worksheet wants to know the slab area, how much of the perimeter of that slab is exposed to the air, and what the U value of that slab is.  Since my entire Bunkhouse is exposed to the air, I listed the full area of the floor and perimeter.  I used the U value of my floor assembly which includes a steel layer for the trailer and a mesh rodent barrier. 

My floor slab type is “Suspended Floor” so I check that box and move to the area where I enter the “Suspended Floor” technical details.  This is where I once again need to pay attention to what the PHPP is looking for.  The Ucrawl is asking for the U value of the ground surface.  If it is insulated you would use that value, if not, the PHPP says 5.9 W/(m2K) is used.  For my calculation at this point I will assume that I am parking the Bunkhouse over bare ground. 

Next the PHPP wants to know how tall the Crawl Space Wall is.  Technically I don’t have one of those, but the trailer bed is 2’ off the ground so I will use that value as an “imaginary wall”.  I see the next field wants a Uvalue for my imaginary wall followed by a field that wants to know how big the ventilation holes are.  I see a loophole here!  I put in a ventilation value that is 100% equal to the size of the wall that the PHPP is expecting to see.  I test this out by changing the Uvalue of my imaginary wall from 900 to .9 and it does not affect the final numbers.  If I remove the ventilation numbers, the Uvalue numbers for the imaginary wall now make a difference, so I quickly put the 100% ventilation value back in.  

The Additional Thermal Bridge losses at Perimeter are not relevant since the metal is outside my Thermal Envelope.  I’m not worried about the ground water issue, so I am done.  That was practically painless and I didn't need to check with PHI after all.  I do know that PHI will go over this sheet with a fine tooth comb if I end up going for certification and they may question what I have done and make some adjustments, but I am feeling pretty confident.  I also feel like there could possibly be the potential to come back and add an insulated skirt to the Bunkhouse so that I have some benefit of a crawlspace if I need to.  I might look at that in the future.

Since I didn’t get to the Annual Heating Demand and Monthly Method sheets this time, I will look at those next week.

Putting Passive House to the Test! Pt. 27g PHPP inputs of Non-PH certified Windows

In this part we will take information about a set of windows that are not certified by PHI (and therefore not included as a choice in the PHPP) and add that information into the PHPP.

I chose to use the Zola Window information for this exercise because their brochure included the necessary values that we will need to fill in the glazing and frame information  in the PHPP and run the Psi calculations in the next blog installment.  If the brochures or website for the windows you are interested in do not have the specific information, ask the company.  

First, let me run through the very quick and basic explanation of COG (center of glass) and EG (edge of glass) as it is used in ASHRAE and ISO calcs to figure out the Ug value (U value of the glazing).  ASHRAE divides the window into areas where the spacer affects the Uvalue of the glazing (Ueg – the outer 2.5 inches of glazing) and areas that are not affected by the spacer (Ucog – glazing not in the outer 2.5 inches).  ISO doesn’t use this edge of glass region separation in their calculation, and instead looks at how the spacer affects the glazing in a linear way along the edge intersection of the glazing and the spacer.  Here are the two formulas that I found in a 2007 LBNL report on State-of-the-Art Highly Insulating Window Frames – Research and Market Review 

If you need to give your inner window geek a thrill, the report has much more detail on these equations that you can check out in section 2.1 Thermal Transmittance (U-Value) which starts on page 8.

So, for entering the glazing of a window we use the center of glass u value to enter into the Win Type worksheet as well as the SHGC value which is equivalent to the G value that Europe uses.

To enter the Frame information on the Windows worksheet, we need the U value of the frame (Uf) and NOT the U value of the entire window assembly (Uw).  This is where you will need to be careful with what information you are looking at.  Full Frame or Overall window performance are the Uw and include the glass U value in its calculation.  If you notice in the above example, the glass has the best U value, the frame the worst, and the total assembly falls somewhere in between.  This is why you need to make sure you are looking at the U of just the frame and not the entire window - inputting the total window U value instead of the frame u value will give you a too good result in your PHPP.  Ultimately this will get caught - best to look out for it before it means your project doesn't get certified!

This gives us most of the information that we need to enter a non-PH certified window into the PHPP.  We still need to calculate the Psi G and the Psi Install.  I covered the general information of how to do this in a previous article called “The ABC’s of the PHPP – Pt 4b The Psi-lence of the Jambs” Next I will use this window information and do those calculations.

Up next – taking non-certified PH window information and determining Psi G and Psi Install values

Putting Passive House to the Test! Pt. 27d Certified Window Glazing in the PHPP

Let’s look at some of the certified glazing units available in the PHPP and figure out what all the notations mean. 

The first thing you will notice is that there are 6 manufacturers that have had their glazing certified through PHI.  They each have several choices for glazing, and each choice has a cryptic series of numbers and slashes after it.  These numbers and slashes represent the panes of glass, spacers, and the position of any coating.  I decided to compare 2 Interpane glazing units that appear almost the same in the PHPP, except the low-e coating is located in a different position.  I wanted to see what kind of change to expect when I see a similar configuration like this.  I also understand that the glass on each unit could be different - that information is not supplied in the PHPP but would be available from the manufacturer.  Here are the glazing units I wanted to compare:

INTERPANE - iPlus 3CE (4:/12/4/12/:4 Krypton 90%)

INTERPANE - iPlus 3CLS (4/12/:4/12/:4 Kr 90%) 

First, let us decode the numbers and slashes for each of the Interpane glazing units I chose.  You will see the numbers and slashes are all in the same order, but the “:” is located in slightly different positions.  This “:” is the designation for the location of the low-e coating.  The numbers tell us, from exterior to interior, the order of the assembled components and their thickness.  So for these assemblies, we find 4mm glass, 12mm spacer, 4mm glass, 12mm spacer, and 4mm glass.  

Each pane of glass has two surfaces, and these are numbered from 1 to 6 starting with the exterior surface.  The first “:” that we come to on the iPlus 3CE unit indicates that the low-e coating is located on surface 2 of the first pane because the “:” is located to the right side of the number.  The second “:” that we come to indicates that it is located on surface 5 of the last pane of glass because it is located to the left of the number.  You will note that the 3CLS glazing units’ first low-e coating doesn’t get applied to surface 2, but rather it is placed on surface 3 on the second pane of glass. The positioning of the low-e coating changes the way heat is allowed to pass through a window glazing unit.  This knowledge is important when designing highly energy efficient buildings like Passive Houses.

Finally, we see that there is a designation for 90% Krypton gas to be used in both glazing units.  This will be what is filled in between the glass panes where the spacer is located. 

So how do these two units compare when tested?  The following chart shows that there is a slight difference in the Ug value .5 for the 3CE unit, .6 for the 3CLS unit.  Their Vt values for Visible Light Transmittance is almost the same, with the 3CE unit allowing 72% of the visible light to be transmitted and the 3CLS unit allowing 73%.  There are a few other differences across the chart, most likely from different glass compositions, but let’s look at the SHGC (represented by the European “G” value) to see how much heat they are allowing to get through the window.  The 3CE unit allows 50% of the heat through.  The 3CLS unit allows 61%.  That is an 11% difference in how much heat is allowed through the units.  That is significant enough to make the SHGC a key factor when choosing between these two packages.  

This was just comparing two window packages made by one certified Passive House manufacturer.  In the PHPP you will see the Ug and G values given for the certified window glazing products.  The Vt and other information should be available at the manufacturers websites.  When comparing to non-PH certified window manufacturers, realize that PHI will have the last word on what they will accept for the performance numbers of those packages.  Be sure to check with them early on in the design phase if you are planning to apply for PHI certification of your project and will be using non-certified Passive House components.

Up Next – Talking to Window vendors at the PHNW Spring Conference in Seattle.  (Join us Friday, March 15^th at the Seattle Pacific University Campus either in person or on our Webinar. Details at PHNW.org.)

Putting Passive House to the Test! Pt. 26 - Back to the PHPP

This week we get back to the PHPP.  I went through the exercise to see what kind of materials that I wanted to use for the walls of the bunkhouse and was attracted to an exoskeleton idea.  Now I need to see if that idea is worth pursuing in the PHPP.

In the front portion of the PHPP manual is a section called First Steps.  It shows you the basic information you need to use the PHPP for determining if your project will meet the annual heat demand requirement.  There are only a few worksheets needed for this step – The Annual Heating Demand worksheet which uses information from the U-Values, Areas, Windows, and Ventilation worksheets.  I started with the Verification worksheet to tell it the general use info and enclosed volume.  That lead me to also fill in the Climate Data sheet where I selected the Seattle climate.

Going with my exoskeleton idea I filled in the U-Values worksheet for the different wall, ceiling, and floor types I am using.  At this point the walls are all the same, but in case I need to tweak the structure for a different material or amount of steel in the exoskeleton I decided to do the short North wall and the tall South wall separate from the long East and West Walls.    So I have 3 wall types (long, short, and tall) as well as a ceiling and floor assembly itemized on the U-Values worksheet.

By filling in the U-Values worksheet, it populates the U-List worksheet with just the basic information of the assembly – the name, thickness, and the U value.  This is a worksheet that you do not need to generally do anything to.  The information will appear as selections of assemblies that you can choose on the Areas page when you get to that.

The Areas page is where I went next.  This page will layout the basic envelope of the building – how big the walls are and how many of them there are.  Interestingly enough, this worksheet does not set what direction the walls are facing (even though I have called them North, South, etc.)  The Windows worksheet is where the PHPP figures out how the structure is oriented.  We’ll look at that when we get over there.

On the Areas worksheet you will see information in the top left section on different groups of areas and what temperature zone they are in.  I added a group for my flatbed trailer since it will be ambient and not ground oriented. 

Below this section is the Areas Input section.  This is where you will detail your treated floor area, doors, and construction assemblies used.  Below that is the area for thermal bridges.   At this time I am not filling in the information about the thermal bridges because I have not determined what those are.  I will be running THERM calcs on the construction to see what needs to be filled in there (if any).

At this point I have detailed my construction assemblies, listed them on the areas page, picked a random door (Optiwin FrostKorken), set my climate, and told the PHPP the volume and treated floor area.  For this “first steps” exercise I will next go to the Windows page, but since I have yet to look into windows, we will go there next week.

Because I was curious, I popped back over to the Verification page to see just how the Bunkhouse was doing.  As you would expect, it wasn’t meeting the heat demand requirement.  Then I grinned, switched the climate location to Phoenix… and it passes!  O.k., it has no windows or any electrical stuff, and hasn’t been pressure tested, but for a brief moment I felt excitement.  Hopefully I will get there with my present climate, but not tonight. 

Up Next – Picking out windows for the Passive Bunkhouse.