The ABC's of the PHPP - Part 7 Heating Load - Put a sweater on, I'm cold!

Growing up my Mom would always tell me to put a sweater on because she was cold.  A lot of people worry that without a big old furnace like they are used to they will freeze in a Passive House and have to put a sweater on… a great BIG sweater.  If your Passive House is situated on a site in a climate that cannot provide all the desired heat through Solar Gains and internal gains such as heat produced by the equipment or people inside, you will need a sweater… an even bigger sweater than you can imagine… a HOUSE sized sweater!

O.K., that was just the slightest bit melodramatic and I am sure the fine folks in Darmstadt are sure I have lost it this time, but stick with me.  When a Passive House is designed all possible “free” heat is planned for.  The calculations of the PHPP are so extremely intricate that they even take into consideration the few inches of shading your window reveal supplies.  How many people look at a window reveal and figure out its heat shading potential???

The PHPP also sorts out just how much heat is going to be escaping when the temperatures drop in the winter or sneaking in when the temperatures rise in the summer.  During the winter the expected temperatures will be modeled and the house design will be sized to keep the residents within the comfort zone.  But what if there is no more “free” heat from solar gain, or internal heat gains and there are just a few days where it might get colder than you would like?  That’s when your house needs a sweater to help with the heating load.  I say a sweater instead of a full-fledged furnace because that’s what the difference is.  You may need more heat, but not to the btu-blasting level you have grown used to in a non-Passive House. 

The Passive House consultant will be able to tell if additional shading such as blinds, trellises, or other devices will help in the summer and they will also know when all the measures just won’t keep the house comfortable and some additional cooling may be needed.  It might even be possible that for your particular climate conditions you could require a little additional heat in the winter and a little additional cooling in the summer.  In that case perhaps a mini-split would be sufficient to provide what is needed. 

Whatever your needs are, they will be specific to your site, location, and project design.  Your Passive House consultant will need to work with your plans and the PHPP to come up with the optimum arrangement that will give you a project that is expected to operate to the PHPP standard.  If you are that Passive House Consultant and have not yet seen the metric version of the PHPP, it may surprise you that not all the climate data has heating and cooling load information as seen above on this screen capture of a San Fancisco, CA climate data page.  This is because PHI uses very specific methods to calculate the heating and cooling loads of a Passive House project due to the longer time it takes a Passive House to heat up or cool down and those methods require a lot of calculations that have not yet been done for all locations.    

Because it takes so much dynamic simulation modeling and there are locations that have yet to have those loads calculated, it will take time to fill in all the blanks – but PHI is working on it and are putting together databases of information that will be available to the Passive House community.  In the meantime, if you are in need of those figures, they can calculate them for your specific location for a fee.  There are also figures available through Meteotest who have put together climate information in a software package called Meteonorm.  Those figures are not PHI certified, and would have to be if you used them, but they can be a place to start.  I asked Meteotest if the Small Planet Workshop could purchase the software and supply the heating and cooling load data to the purchasers of the PHPP but was informed that the individual user would have to acquire their own version of Meteonorm to get the heating and cooling load data.

I contacted PHI about the missing heating and cooling load information and the potential for a user to have to acquire additional data to complete the PHPP.  I was told by Jessica Grove-Smith of the PHI that those figures would not be necessary for completing the PHPP:  “The PHPP does include a number of climate data sets for the US, which can be used as a basis for certification – the PHPP purchaser is therefore not necessarily required to make an additional purchase for his/her project completion (heating and cooling data is not required to for the PHPP to work). We do not mean to mislead anyone. The PHPP is a stand-alone tool which requires a reliable data input. Acquiring some of the project specific data can incur additional costs e.g. calculating a thermal bridge, determining component specifications or local climate data. “  

Jessica also said “Additional PHPP climate data is only required for some projects, the cost of climate data generation & validation is therefore not included in standard certification prices. We are currently working on creating a database of verified climate data worldwide and we make whatever data we already have available to all PHPP users free of charge. As the PH standard is not yet established worldwide there are some locations for which data has not yet been generated. “ 

I was curious as to how, as a user, you could calculate a project without knowing those figures and I went to the PHPP.  Looking under the hood (and relying on Google Translate for the German notes I found) I discovered that there are default numbers that are used in calculations when the actual numbers are missing.  Above are just some of the "under the hood" calculations that are not immediately visible to the user on the Heating Load worksheet (I added the red translations) - but rest assured, the PHPP has one heck of a powerful engine under the hood!  If you are using the Heating Load worksheet and see the error message “Climate data contain no heating load data!” this will let you know to add the data if you have it, get it calculated if you need it, or rely on the default numbers to finish the PHPP.

PHI certifies projects that are limited to a maximum Specific Space Heating Demand of 15 kwh/(m2a) OR a maximum heating load of 10W/m2.  If you are relying on the heating load to meet the PHPP requirements you will need the accurate calculations done for the heating and cooling loads for your project.  If you are not relying on the Heating Load to meet the PHPP requirements and instead are focusing on the Specific Space Heating Demand requirements the default figures will be sufficient for the other formulas that do not require such specific calculations as the exact heating load.

As to entering data on the Heating Load worksheet - there are two separate areas.  The first one only has one cell where you can change the input max. supply air temperature, but only to a lower number if your system can not generate the max 52deg C that is the limit allowed.  Additionally, if you have a specific room that may require its own heat source there is a individual room worksheet located on the right side of the Heating Load worksheet where you can calculate an individual room's heating and ventilation needs.  Once completed, the worksheet will tell you if it thinks a separate heating circuit may be needed, or if it expects no problems.

Next up – Did we make the requirements?