In Part 1, we discussed how energy models inform HVAC systems design to reduce building energy usage (https://bit.ly/3EW689E). This article looks beyond the building systems, focusing on ways an energy model can help optimize the architectural design to lower energy use.

Architecture history and the application of HVAC systems

With the diversification of building functions and the growing demand for stable environmental conditions and improved indoor air quality, the energy consumption associated with mechanical, electrical and plumbing (MEP) systems has steadily increased over the years. 

Before the advent of MEP systems, especially HVAC systems, which have been around for a little more than a century, architects had spent thousands of years striving to create livable indoor environments balanced with their specific climate. Alongside designing aesthetically pleasing structures, they employed various passive design strategies to enhance comfort.

Examples of architectural ingenuity shaped by climate include Thailand’s treehouses, elevated for airflow and flood protection in the humid tropics; Alaska’s igloos, using compacted snow as insulation against freezing temperatures; and adobe structures in arid regions, with thick walls to regulate extreme temperature swings. These designs showcase how architecture adapts to local environments for comfort and practicality. 

In ancient Rome, facilities were also built with radiant flooring systems for use in winter, using heat from cooking to pass through a raised floor before being vented from the opposite corner.

These designs are a testament to the wisdom and creativity of early architects. Importantly, the need for passive design did not disappear with the introduction of HVAC systems. On the contrary, HVAC and passive designs can complement each other! When passive design alone cannot fully meet the comfort requirements of a building, HVAC systems fill in the gaps. 

While adding HVAC systems inevitably increases energy consumption, effective passive design can significantly reduce the reliance on HVAC systems and their energy, particularly the heating and cooling load.

At this point, let’s investigate the concepts of building load and building energy:

• Building load refers to the heating and cooling energy needed for the HVAC system to condition the building at the desired temperature, humidity and ventilation. Note that it is only related to the building design; it does not account for the HVAC system efficiency.

• Building energy use in this context refers to the portion of electricity or gas needed to operate the building’s HVAC systems. In its simplest terms, the HVAC system efficiency is expressed as a ratio of building load divided by the building energy use associated with the HVAC systems. 

Note that for nonlaboratory building programs, while different HVAC systems may have different energy consumptions, the building load remains unchanged. In these applications, the biggest impact of lowering energy use comes from first reducing the building load through passive design.

The first part of this series focused on the use of energy modeling to predict both the building load and the associated building energy use for a variety of HVAC system types. That article started with a fixed building configuration and looked to optimize HVAC systems. 

In this article, we instead examine the use of energy modeling and other climate analysis tools to optimize the building load independently of the HVAC systems that may be employed. The insights gained from this analysis then inform how the architect designs and organizes the building program to lower energy use.

Using climate analysis and energy modeling to lower building load 

1. Climate analysis. At the beginning of the project, the design teams do not have much information on the building concept, but the site and local climate is known. 

Climate analysis tools can provide critical information to inform the characteristics of the climate that can then be used to inform the building layout. For example, climate analysis can include sun exposure, temperature distribution, cloud cover, prevailing wind directions, comfort blocking wind opportunities, and more. 

An initial solar exposure analysis (Figure 1) was conducted in Lakewood, Colorado (outside of Denver), at the latitude of 39.7 degrees. During the summer solstice, the sun reaches a maximum altitude of 79 degrees, with a minimum altitude of 24 degrees during the winter solstice. This low-angle winter sun can provide passive heating through window glazing, while the high-angle solar radiation can be blocked with horizontal sunshades during the summer. 

As expected, the most solar exposure hours occur from the south, with 51% of those hours from the southeast in the morning. This is most useful for passive heating, with 49% of the hours from the southwest in the afternoon. 

To protect against overheating in summer months, any glazing on the facade should be blocked with external shading elements or a roof overhang, with considerations for low-angle sun from the west and east causing the most heat gain in the morning and evening.

2. Orientation study. Based on the climate analysis and prior experience, the designer might already have an idea about a preferred building orientation, but some site-specific infrastructure has the potential to impact that approach. As a result, it is highly recommended to study solar angles and shading concepts on the site and then compare the heating and cooling load for the specific space types. 

This then gives the designer a feel for what approaches work best for different exposures to inform the building’s conceptual design.

3. Shoebox model. Before the architectural plans become fully developed in the early design phase, a shoebox energy model of the building massing is recommended to compare the heating and cooling load for different building design options. The results of these studies then inform building placement on the site while including optimization for energy performance. 

4. Facade shading study. After the building orientation and shape are designed, the design will then focus on solutions for fenestration and shading. As seen in solar radiation studies for this site (Figure 2), there is passive heating potential along the south facade. Understanding this opportunity, our team optimized the south scrim geometry to maximize daylight, minimize glare, maximize beneficial solar radiation, maximize views and reduce peak loads. 

Solar radiation along the southwest facade is less beneficial due to the warmer afternoon temperatures and anticipated interior loads. As a result, the design incorporates shrouds and self-shading strategies, such as an extended second-floor balcony and third-floor fascia, to protect the glazing from low-angle solar radiation while maintaining good interior daylight. Note that the break room balcony provides effective horizontal shading of the two-story glazed lobby below.

5. Whole-building performance comparison. Many times, the impact of the previous design strategy on the building load cannot be decoupled but must be evaluated together. The same window’s impact on the building’s performance varies based on the orientation and shape of the building. 

Benchmark energy models can be defined by Zerotool or the I2SL laboratory benchmarking tool, depending on the building type, to compare whole building performance. Figure 3 is an energy model output from IES VE software.

6. Indoor daylighting analysis. Note that energy usage is not the only factor to evaluate indoor environmental comfort. Daylighting and glare also play an important role and will eventually impact the building’s energy usage. Larger window areas with low thermal insulation translate to increased heating and cooling loads, but the induced solar heat gain can warm the space on a frozen morning. Induced daylight reduces the unnecessary artificial lighting during the day and brightens people’s moods. 

When studying indoor daylighting, the two most important indexes are: 

• Useful daylight illuminance. This is a daylight availability metric for the percentage of the occupied time (hours) when a target range of daylight illuminances is met by daylight. 

• Spatial disturbing glare. This is the percentage of views across the regularly occupied space where the experience is disturbing or intolerable glare for at least 5% of occupied hours.

7. Indoor thermal study. When studying the indoor thermal comfort, the two most important indexes are: 

• Predictive mean vote. This is a key indoor thermal comfort index, factoring in variables such as temperature, humidity, air velocity and clothing insulation to predict comfort levels on a scale from -3 (too cold) to +3 (too hot), with 0 being neutral. 

• Thermal comfort percent. This is the percentage of occupied time when the conditions are considered acceptable/comfortable. 

8. Outdoor daylighting analysis tool. As the interactions between buildings and the associated outdoor spaces are also important to the building function, more tools have been developed for outdoor daylighting analysis. 

For example, a Ray Tracing study on how sunlight bounces out of a building and affects solar radiation in the planned outdoor spaces to avoid extreme glare can maximize the use of those proposed outdoor amenities.

9. Outdoor thermal study tool. Similar to the indoor thermal study, an outdoor thermal analysis can be used to study the temperature impacts of building features. For example, examining how the canopy design also impacts associated outdoor spaces by comparing the temperature distribution before and after adding the canopy.

10. Parametric optimization. This refers to the process of finding the best values of certain parameters within a given system or model. In our case, we use different parameters to represent different glazing and shading designs, including the length and width of the window along with the distance between them, together with the shading ratio and type, as all these parameters impact daylighting and energy usage. 

The goal of these studies is to find the best combination of all the parameter values, resulting in the maximum indoor environment comfort with the lowest building load. 

For example, 48 design options/combinations of the fenestration were compared for the same project, as shown in Figure 4.

Of those combinations, the best two potential options are 2-foot spacing with 60-degree, 18-inch-deep fins with an 88% window wall ratio fenestration; and 3-foot spacing with 40-degree, 12-inch-deep fins with a 56% window wall ratio fenestration as shown in Figure 5. The deeper louvers allow for less rotation, and larger spacing benefits views and thermal comfort. 

Among all the design options, these were selected as they achieve a good balance among all the key design considerations: view, daylight, glare, peak load and aesthetics. The saving of the peak cooling load also reduces HVAC equipment size and saves the initial cost for an HVAC system. 

With the support of climate analysis and energy modeling, the architectural designer and mechanical engineer can collaborate to find a balanced approach that maximizes building performance while maintaining the design intent. 

Additional energy reduction strategies

Figure 6 showcases additional energy reduction strategies that are proposed beyond the above building load optimization as follows:

1. Improved building envelope. Increased roof and wall insulation, triple pane windows and high-performance framing systems limit building heat losses.

2. High-performance exhaust heat recovery. Waste heat from laboratory exhaust air is recovered and used to precondition outside air for ventilation, with no potential for cross-contamination.

3. Active chilled beams. Required ventilation for space conditioning is reduced. Reduced ventilation lowers energy to condition, and reduced airflow lowers fan energy.

4. Seasonal thermal storage. Use of geothermal exchange bores allows waste heat in summer to be stored underground to then recover in winter months to reduce building energy use. 

5. Solar photovoltaic arrays. These generate electric power throughout the year to offset building energy use. Solar arrays above parking areas also provide beneficial shading in summer months.

6. Heat recovery chillers. Coupled with the geothermal system, this equipment supports the building’s heating and cooling loads. The same equipment used to recover this energy also supports simultaneous heating and cooling at other times of the year, greatly reducing energy use and limiting waste.

Architecture and engineering play important roles in affecting building energy performance, whether it’s the building load or the associated HVAC system efficiency. Climate analysis and energy modeling are a bridge between these disciplines, enabling a smarter, climate-responsive design that reduces demand while enhancing comfort and sustainability. 

By integrating passive strategies together with high-efficiency HVAC systems, architects and engineers can create high-performance buildings that meet present needs and respond to energy challenges in the future.

Ting Cai is an energy modeler with SmithGroup at its Phoenix office. She has experience with laboratories, hospitals and healthcare facilities, higher education classrooms and office buildings.

JB Pham, a senior designer at SmithGroup Phoenix, combines his passion and experience to design high-performing laboratories and higher education spaces.