Model Geometry
For all model results show here, the following building geometry was used. This geometry is based on the drawings/models received on January 5, 2024. The model geometry used for this assessment includes both the building itself as well as the local shading context. For details on the context shading see the windows site shading section.
* Floor Area:
- For any/all PHI energy model results, interior ’treated’ floor areas (TFA) are used for these cases. These areas are based on the European Standard for Residential Floor areas. For more for details as to which areas are included and which are excluded, see the standard DIN #277.
- For any/all Phius energy model results, interior conditioned floor areas (iCFA) are used for these cases. These areas are based on the Phius CORE 2021 rules, and more information can be found in the Phius rules document.
Site Energy
‘Site Energy’ represents the energy purchased by the building and delivered to the site by the utility. This is the most typical energy use figure assessed when considering a site ‘Net-Zero’ building energy balance, or when considering the annual cost of energy for the building. This site-energy total is made up of 6 main groups: heating, cooling, hot-water, appliances, lighting, and equipment like pumps and fans.
In order to assess the performance of the home across a range of options, we have simulated 5 distinct variants with different energy efficiency measures (see the ‘Model Variants’ for details on the specific variant inputs). Below we show the site-energy consumption for the 5 variants of the building modeled. Note that the ‘Baseline’ variant in this case is the ‘Code Minimum’ for the building location. We then added 3 sets of ‘improvements’, and finally show a full ‘Passive House’ variant for comparison. In this case we are recommending the Level 2 improvements for this home in order to balance the cost and benefit of the improvements.
CO2 Emissions
Carbon Dioxide and other types of pollution which results from energy consumption are mainly responsible for the increased warming of the earth’s atmosphere and water. In order to reduce the risk of global climate change it is important to reduce all CO2e (CO2 Equivalent) emissions related to buildings, industry and transportation across all sectors. While there is much debate about the specific targets these reductions should achieve, one useful method suggests that by 2030 each individual will need to meet an annual ‘Carbon Budget’ of roughly 2.3 tons-CO2e per person for all activities. This would mean that an average individual’s annual carbon emissions might include approximately 1 ton-CO2e / year related to housing and building inhabitation, 1 ton-CO2e / year for transportation and another 0.3 tons-CO2e / year for food. For reference, a single US-to-Europe round trip flight currently releases approximately 4 tons of warming gases into the atmosphere. This 1 ton/person target for building emissions gives us a useful benchmark for this home’s annual CO2e emissions. Given an average annual occupancy of approximately 3-5 people, this home should ideally see a total annual CO2e emissions footprint of less than about 3-5 tons-CO2e / year.
Based on the modeled source energy and fuel types for the various energy uses of the building we can approximate the average annual CO2e emissions which will result. CO2e emission totals shown below are those which result from fuel usage by the home for heating, cooling, hot-water and all other plug-loads. The total amount of CO2e emitted as a result of each use-type depends on both the amount of fuel used as well as the type of fuel (gas, electricity, etc..). Although fuel-fired heating systems are permitted by Code, for this evaluation we have modeled all variants with electric-powered heat-pump systems only.
Output Emission Rates used are from the NEWE (North East) Subregion. For more information on these factors see the EPA eGRID Data Explorer and Guidance on the Use of eGRID Output Emission Rates. Source Energy Factors for all fuel types are taken from the EPA EnergyStar Portfolio Manager Technical Reference (2018)
PH Certification Thresholds
In order to evaluate a building’s performance, Total Annual Energy consumption is key, as shown above. However, in addition to this top line figure the the ‘Passive House’ framework also suggests that in addition to meeting the Total Annual Energy target, the building should also meet additional heating and cooling annual energy demand performance targets. It is also useful to compare the peak-heating and peak-cooling loads to the recommended limits for Passive House buildings. While these limits are not required for certification in all cases, it is still good practice to attempt to meet them where possible and where the home fails to meet them - this is a clear indication that improvements are possible.
Shown below are results for these assessment metrics, for each of the tested variants.
Note that the Improvements (Level 1 / 2 / 3) reduce the heating energy and peak-heat load significantly. However these same measures (more insulation, etc..) also increase the cooling energy and peak-cooling load. However the cooling, even under the full “Passive House” variant, are well below the targets and the increase in cooling energy is more than offset by the reduction in heating energy in the cases evaluated here.
Model Variants
As shown in the results detailed above, in order to assess the building performance we have tested the building in five distinct configurations:
Code Minimum: A version which just meets the Massachusetts Energy Code 2021 / Zone 5 code minimums for insulation envelope R-Values, air-tightness and equipment efficiencies.
Improved [Level 1 / 2 / 3]: These 3 versions improve the envelope specifications to various (good / better / great) levels of performance. These improvements include Wall, Roof, and Floor R-Values, window U-Values, improved air-tightness, and less thermal-bridging. In the case here, we recommend the Level 2 Improvements as the best balance of cost and performance. Note that Level-2 and Level-3 also include improvements to the ventilation system along with the improvements to the envelope.
Phius Certified: A version which further improves the building’s performance specifications until it is able to achieve the Phius CORE Certification level. While it is possible to achieve this level of performance in this climate zone, it is not recommended as the cost of achieving this level of performance is likely fairly high in this case.
A full outline of tested variant inputs and key outputs can be found in the table below:
* Envelope R-Values: Note that effective R-Values (including repeating thermal bridges) are shown here. These values are taken from the Massachusetts Energy Code 2021 / Zone 5 minimum compliance values.
** Thermal Bridging Allowance: This is a % increase in the overall heat-loss of the building. Instead of performing detailed Thermal Bridging calculations, this value is based on past experience only and should be understood as a rough estimate or allowance.
Climate
For all the modeled cases shown in the following sections, climate data from the nearest weather station was used.
The data from this climate set is illustrated here for reference purposes. It should be noted that for the PHPP model, monthly average climate data are used and therefore may appear different from the more typical ASHRAE hourly data shown in some other US Energy Modeling programs. The monthly data is all derived from the same sources (local weather stations) as the typical ASHRAE data however.
PH Certifications
The following is for informational purposes only.
Passive House is the most challenging energy standard for buildings employed around the world today, with a strict cap on heating, cooling, hot water, lighting and appliance energy use. By successfully employing Passive House methods, a comfortable, durable and sustainable building can be created which uses only a tiny fraction of the energy that a ‘conventionally built’ structure would.
The ‘Passive House’ standard was first developed as a standard for new construction by the Passive House Institute (PHI) in the early 1990’s. Since that time, there have been several new pathways to certification developed which are now available to buildings. While we do not recommend that this building pursue this level of performance, the Passive House certification is used as a good ‘reference’ level to show what a high-performance home would perform like in this climate. Passive House buildings can be certified in various ways, including:
Passive House Certifications
The 'Passive House' standard was first developed as a standard for new construction by the Passive House Institute (PHI) in the early 1990’s. Since that time, there have been several new pathways to certification developed which are now available to buildings. While we do not recommend that this building pursue this level of performance, the Passive House certification is used as a good 'reference' level to show what a high-performance home would perform like in this climate. Passive House buildings can be certified in various ways, including:
+ PHI New Construction
+ PHI Low Energy Building
The Phius standard was first developed as a standard for new construction in 2015 by the Passive House Institute of the US (Phius). Since that time, there have been several updates and new pathways to certification developed which are now available for development teams. Currently, Phius buildings can be certified in various ways, including:
+ Phius CORE 2021
+ Phius Source Zero 2021
