The Heart of HVAC Design

the heart of hvac design image

Many in the building industry believe that the heart of a home is the HVAC system, but what is the heart of the HVAC system?

Just as a heart has four chambers that work together to pump blood around the body, the HVAC system has four components that, when integrated, create a system that works in unison to create comfort in the home.

  1. Manual J evaluates and describes the tight well-defined and constructed thermal envelope.
  2. Manual S provides guidance for how to properly size the heating and cooling equipment.
  3. Manual D directs the design of the duct system that will deliver conditioned air around the home.
  4. The ASHRAE 62.2 standard ensures that we have the proper balance between air tightness, efficiency, durability and comfort with ventilation needed for the occupants and background moisture control.

In the heart of the HVAC System: Manual J

Manual J is used to determine the heating and cooling load for the house and directs us toward the heart of the HVAC design. The objective of the heating and cooling load is to tell the designer how much energy is needed to achieve the design goals with a specific thermal envelope and piece of mechanical equipment. Heat moves from warm to cold and the thermal envelope retards or slows that flow. The International Energy Conservation Code (IECC) and the International Building code (IRC) both lay the ground work for the HVAC design.  These codes give us design temperatures.  In other words, they tell us the temperature difference (or Delta T) between inside and outside in the winter and summer seasons.

R-Values & U-Values, the Thermal Envelope

The R-values and U-values of the thermal envelope resist or slow the movement of energy from the inside to the outside in the winter and from the outside to the inside in the summer through the building envelope. The thermal envelope happens to be one of the most important components in the HVAC heart because its execution determines the success of most of the other interactions that take place to allow the home to be efficient, durable, safe, and comfortable. The IECC lays out climate zone-specific minimum R-values and U-values and construction installation techniques that have been deemed to create comfort in each area of the country.

When a designer inputs the specification for the insulation, windows, air barriers, and assemblies into the software to create the heating and cooling load for the house at the summer and winter design temperatures, the assumption is that the installation of the specification is perfect. The installed R-value is achieved, the house is airtight, and there is complete alignment between the thermal barrier and the air barrier of the home, as required by the IECC to ensure that the energy generated by the furnace and AC system will heat or cool the house during worst case conditions. A well-designed and constructed thermal envelope better resists the flow of energy through its assemblies. If the insulation, airtightness, and alignment of the air barrier and thermal barriers of the home are not executed well, modern HVAC systems that are not correctly sized could have difficulty maintaining comfort in the home. The ultimate objective is for the systems to run continuously to maintain the indoor design temperature when the worst case outdoor temperature has been reached or exceeded for those few hours of a day.  It turns out that the HVAC design process already has a built in safety net. If you thought that oversizing the system is a technique to ensure comfort, you would be wrong.  In our modern homes oversizing leads to equipment that will not perform properly – freezing coils, short cycles, etc.

Our homes are integrated systems that rely on each component of the system to work in unison with the other components. This is why EnergyLogic begins our HVAC design process with an understanding that we will evaluate the construction of the thermal envelope and its compliance with the requirements of codes and programs that aim to ensure that high-performance homes perform. To learn more about EnergyLogic’s HVAC design process, visit our New Residential HVAC Design page.

 

Robby Schwarz (faked)

Who to Contact:

Robby Schwarz
Principal, Director of Builder Relations

Email Robby
720-838-0677

Why all HERS®/ERI Index Scores are Increasing Nationwide

It is important to understand the Home Energy Rating System (HERS®) and Energy Rating Index (ERI) are describing the same thing. HERS is a proprietary acronym created by the Residential Energy Services Network (RESNET), so the term ERI has been used for the code language. RESNET is the governing and standard setting body of the home energy rating world. RESNET recently created the ANSI/RESNET/ICC 301-2014 standard that describes how the Index score is developed. Within the 2015 IECC language that used to describe how to develop an ERI score has been replaced in the 2018 IECC with the ANSI 301 standard. In addition, the standard has now been incorporated into every software used to develop a HERS® or ERI Index score.

The ANSI standard change has, and will, cause all HERS/or ERI index scores to increase across the country. Due to this score increase and other fixed mandatory requirements in the ERI pathway, it is unlikely that jurisdictions will see builders using the ERI path for quite some time.

For more information on why this is happening, please refer to the following article: HERS® Energy Rating Index Scores are Going Up!

Software developers have incorporated the new ANSI/RESNET/ICC 301-2014 standard into their systems. As stated before, they are all consistently seeing the HERS/ERI index scores increase. Currently, there are three software systems available:

Ekotrope

REM/Rate™

EnergyGauge®

EnergyLogic is in the process of transitioning to the Ekotrope compliance software which will change the look of the reports but will not affect the content of the reports. Click here to see a sample Ekotrope report. All three software versions have incorporated reference homes to developed code compliance documents for the UA Tradeoff, Simulated Performance, and Energy Rating Index pathways through the energy codes.

What is a reference home?

Imagine your two hands are two homes that are geometric twins of each other. Your left hand, the reference home, is a house built with the energy and aesthetic features defined by the code which uses a quantifiable amount of energy that the code has deemed to be the minimum amount allowed by the jurisdiction.  Your right hand is the home you want to build, the proposed design, with the energy and aesthetic features you believe, are best to achieve whatever goal you have for the home: cost- effectiveness, safety, aesthetic beauty, comfort, durability, efficiency or livability. Your home, the proposed design, on the right, is compared to the code reference home on the left and if your home’s performance is equal to or better than the reference home it complies with the code and can be permitted to be built. The jurisdiction, an approved third-party, or both will inspect, verify, and report that the home was built as proposed in order for the certificate of occupancy to be released. 

For more detailed information, please refer to the following article: Simple Explanation of the IECC

In summary, changes and upgrades to software systems are inevitable. The creation of the ANSI/RESNET/ICC 301-2014 standard was the most impactful, but every version upgrade affects something. As a result, RESNET has developed a standard that governs when Energy Raters must transition to the most recent version of a software.

For more information on this subject, please refer to the following article: Important RESNET® Amendment on Rating Software Changes (Persistence)

 

Robby Schwarz (faked)

Who to Contact:

Robby Schwarz
Principal, Director of Builder Relations

Email Robby
720-838-0677

A Simplified Explanation of the International Energy Conservation Code (IECC)

EnergyLogic is a residential energy services company that specializes in energy code and/or program compliance, generation of the HERS® or ERI index score, third-party risk and quality assurance inspections and diagnostics, as well as HVAC design. Most often we work directly with architects, builders, and developers and it begins with code compliance. This article will focus on explaining the International Energy Conservation Code (IECC).

The IECC is a tool used by jurisdictions to ensure that when new or remodeled homes are built, they achieve a specific quantifiable level of energy efficiency. Although it is a code, it does not mean that it is one-sided. In other words, the energy code is a marvel of flexibility, offering multiple compliance paths in order to help determine the most cost-effective way to build a home that not only meets the performance goals and expectations of our modern world but also includes the design imagination and material integration we desire. Yes, there are boundaries to this game, but there is flexibility as well, to ensure that we can build and live in the homes of our dreams.

Energy code flexibility is discovered in the different compliance paths of the code. A path through the energy code guides one through a series of code sections that, when followed, demonstrate that a building’s design meets the baseline requirements of the code defined by a quantifiable amount of energy use in the home. The quantifiable amount of energy used in a home is defined by a reference home, which the home you want to build is compared to.

What is a reference home?

Imagine your two hands are two homes that are geometric twins of each other. Your left hand, the reference home, is a house built with the energy and aesthetic features defined by the code which uses a quantifiable amount of energy that the code has deemed to be the minimum amount allowed by the jurisdiction.  Your right hand is the home you want to build, the proposed design, with the energy and aesthetic features you believe, are best to achieve whatever goal you have for the home: cost- effectiveness, safety, aesthetic beauty, comfort, durability, efficiency or livability.  Your home, the proposed design, on the right, is compared to the code reference home on the left and if your home’s performance is equal to or better than the reference home it complies with the code and can be permitted to be built.  The jurisdiction, an approved third-party, or both will inspect, verify, and report that the home was built as proposed in order for the certificate of occupancy to be released. 

Important terminology to know:

Mandatory requirements– requirements that must be met in every building design no matter which compliance path is chosen, unless there is a specific exception in the code

Prescriptive requirements – Requirements that must be met by every building, unless an approved tradeoff is utilized or unless there is a specific exception in the code

Tradeoffs – tradeoffs are defined performance features in a home such as R-values, U-values, infiltration, or duct leakage that allow trades to be made between various low and high performing features of a home

Performance approach – An overall performance requirement for the building that replaces the individual prescriptive requirement for building systems and components

Pathways in the IECC

There are four basic pathways through the code, all of which utilize the reference home/proposed design construct described above. The primary difference between the paths is ease of use and flexibility of choice of materials to determine the most cost-effective way to achieve the efficiency goals of the code and the builder.

Prescriptive Path:

The prescriptive path lays out the energy specification, R-values, and U-values, as well as installation techniques that must be used in the home you want to build. If you choose the prescriptive specification level for your home, you must install materials that are equal to or better than those listed in the R-value or U-value tables in the code in order to achieve a level of performance that is equal to or better than the reference homes level of performance.

Area weighted U-value or UA trade-off path (sometimes called the RESCheck Path):

RESCheck is not a compliance path: it is actually a software developed by the Department of Energy to demonstrate Area Weighted U-value (UA) trade off compliance. The pathway uses a tradeoff approach which provides flexibility for builders and designers to determine how they want to create a house.  For example, if a builder wants to install R-38 insulation in an attic rather than the required R-49 as prescribed by the 2015 IECC in climate zone 5, they may be able to trade off the lower energy performance in the attic for better than prescribed energy performance somewhere else in the home, such as foundation insulation.  In this way, the builder has demonstrated that lower R-value performance in the attic can be traded off for higher R-value performance on the foundation.

Simulated performance path:

The simulated performance path builds on the UA method and utilizes whole-house energy analysis to determine compliance with the IECC. As energy moves by conduction, convection, and radiant energy transfer this path offers the most flexibility by not only utilizing R-value and U-value tradeoffs but also allowing tradeoffs of house tightness and duct leakage, among other things. Annual energy costs rather than area weighted U-value is used as the matrix of compliance. In other words, the proposed design’s annual energy cost must be lower than or equal to the code reference home, to demonstrate compliance. Currently, EnergyLogic believes that the Simulated Performance path is the path that best helps builders achieve the most cost-effective and high-performance home to meet the intent of the IECC.

Energy Rating Index (ERI) path:

The Energy Rating Index and the HERS Index are the same. However, the ERI score is used as part of a code compliance path that was adopted in the 2015 IECC. It is important to know that the climate zone specific ERI score is one, but not the only thing required by the pathway. Like all code paths, the ERI path requires that all mandatory features of the code be completed for each home.  In addition, among other things, features such as mechanical equipment and solar, can lower the ERI score; therefore, in order to ensure a sound thermal envelope, a backstop was introduced. A home using the ERI path must use the prescriptive insulation levels outlined in table R402.1.1 of the 2009 IECC.

The 2018 IECC kept the structure of the ERI path while raising the ERI scores in each climate zone. In addition, if solar is installed on a home, the 2018 IECC states that the prescriptive insulation levels outlined in table R402.1.2 of the 2015 IECC must be used.

Robby Schwarz (faked)

Who to Contact:

Robby Schwarz
Principal, Director of Builder Relations

Email Robby
720-838-0677

EnergyLogic Tech Bulletins

EnergyLogic crafts many Tech Bulletins on a variety of subjects to help educate our clients while ensuring that we are all on the same page regarding what is required by a program or a code.

Our Tech Bulletin’s topics range from ventilation to insulation, from fan ducting installation to warm/conditioned crawl space design, and more. Most topics we cover come from questions you ask that need added research and understanding. If necessary, plan sets or scope-of-work documents may be created to address further details for each topic.

Our tech bulletin on bath fan installation is a good example of a topic that initially came from a question that needed a better building science perspective. In consideration of ENERGY STAR® best practices, as well as specific building codes, we are measuring the flow through bath fans more often.

Other Tech Bulletin topics that might be of interest to you can be found on the EnergyLogic Blog. Below you will find a few relevant post links for reference:

Whole-House Ventilation Strategy

Vent caps and fan flow

Training resources to help reduce re-inspections

If you have a topic or situation that you think needs a better-applied building science perspective, please let us know and we will do our best to research your question and get a new Tech Bulletin on the subject.

 

Robby Schwarz (faked)

Who to Contact:

Robby Schwarz
Principal, Director of Builder Relations

Email Robby
720-838-0677

 

EnergyLogic 2016 Accomplishments

Happy New Year!

Before getting too far down the road, we want to take a moment to thank you for your trust in us, and our work. Thank you for allowing us to help you with your code and program compliance, generation of the HERS Index, and quality assurance needs. We hope your new year is prosperous and successful!

We completed just over 4,600 inspections in 2016. That work is broken out in the table to the right. We are not only proud of our people, we are proud to have worked with our partners through such a successful year. We are thankful for the opportunities our partners, and their teams, have provided by allowing us to collaborate with them in reaching their goals.

As we continue to serve your inspection and quality assurance needs, I want to remind you that we are continuing to grow and innovate to better meet the challenges of our industry. Here are a couple of highlights:

  • We have restructured our company to create field teams, which allows us to have better communication both internally and externally. This ensures that our consistency, accuracy, and professionalism perform at its highest level.
  • We have excitedly expanded our service offerings to include water management inspections to complement our existing quality assurance 3rd party work, warranty inspection to better determine warranty issues and solutions, as well as HVAC design and quality installation services.

Lastly, we are continually growing and training our field staff of Raters to be at the top of their game andto maintain our expanding knowledge base and skill set to continue leading the industry.

Thank you. We look forward to a wonderful 2017!

Robby Schwarz and the EnergyLogic Team