This page is about the development of the heating and cooling plan for the Duplicable City Center®. It is purposed to share the specifics of the design, implementation, and maintenance of the complete City Center HVAC and its integration with the automation, monitoring, and control systems.
We discuss this with the following sections:
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The simplest definition of “sustainable heating and cooling” could arguably be heating and cooling that is powered by renewable energy. This approach can be made even more sustainable by integrating passive approaches like careful window placement for non-mechanical heating and venting, use of thermal mass, etc. Design choices like maximally energy efficient windows and doors, choice of insulation, and the air-circulation benefits of domes over square buildings also contribute. In addition to these, we will objectively measure and improve the sustainability of the City Center HVAC system using the open source control and automation systems we’re designing.open source control and automation systems we’re designing. We will open source all the data we gather, everything we learn, and our ongoing modifications and evolutions to help others to more easily learn from, replicate, and/or improve these designs.
Heating and/or cooling in most climates is a significant and important consideration due to the design and equipment needs and associated energy requirements. Our goal in open sourcing the Duplicable City Center HVAC designs, window and door research and installation, insulation decisions, and automation, monitoring, and control systems is to provide useful data for:
This open source aspect of the City Center will additionally contribute to our global-change methodology by functioning as a testing space for HVAC-related equipment and lifestyle changes. Through use of the extensive automation, monitoring, and control systems designed into this building, we’ll be able to objectively gather, compare, and share thousands of data points related to any modifications we choose to implement and/or test.
Adrienne Gould-Choquette: Mechanical Engineer
Aravind Vasudevan: Mechanical Engineer
David Olivero: Mechanical Engineer & Data Scientist
James Nance: Mechanical Engineer
Vamsi Pulugurtha: Mechanical Engineer
The Duplicable City Center has a few unique characteristics: a root cellar, server rooms, an indoor pool, and it is comprised of three geodesic domes. This section shares the calculations we completed comparing standard versus high-efficiency design details. This comparison includes an R-45 insulation for the exterior surfaces of the domes and building insulation, equipment loads, and people loads remaining constant. Two heat load calculations were performed:
Note: The benefits outlined below are just analyzing the effect on the heating and cooling systems. The benefits to building efficiency have much farther reaching benefits. For example, switching to LED lighting from regular incandescent lighting. Incandescent bulbs put off more heat than LED bulbs. This heat is a form of wasted energy which causes increased demand on the cooling system in the summer. By switching to LED bulbs, the reduced heat load to the building means lower cooling costs in the summer and this translate into a smaller capacity cooling system too. In addition to this, the bulbs lower power consumption means less energy requirements, which all means a more comfortable building powered by a smaller array of photovoltaic panels.
A big part of building efficiency is the “tightness” of the building, which is a measure of leakage and airflow though things like outlets, light fixtures, window framing, etc. A tighter building means greater temperature control. One Community’s City Center prototype building will be built in an area with temperatures averaging between 20 and 90 degrees F. The domes are designed for passive cooling during the summer months with backup air conditioning for extreme temperature periods. The winter lows can dip below zero, so during the winter, to avoid drafts, efficiently maintain comfortable temperatures, and maintain proper building air balance, a tightly constructed building is an even more critical consideration.
Building “air tightness” is improved by sealing leakage pathways. Examples of this are:
A source for more information on this is found on in the Building Technologies Program Air Leakage Guide from the US Department of Energy.
Below are the results of One Community’s City Center prototype building comparing an “average building” (a maximum of 0.17 air changes per hour (ACH) in the summer and 0.32 ACH in the winter) to a “tight building” (a maximum of 0.6 ACH in the summer and 0.12 ACH in the winter).
What you see is properly sealing the building makes a significant impact on the results of the heating load calculation. It cuts the impact of outside air infiltration by over 50% for all spaces of the building.
A tight building also comes along with requirement for greater attention to ventilation to ensure the comfort and health of the occupants. Two options when introducing ventilation air into a building are considered for this analysis. The Baseline method is modeled such that the fresh air directly enters the air handling unit’s return. The High Efficiency method is modeled such that the outdoor air is pre-treated to 63 degree fahrenheit, before being introducing it into the air handler.
The impact of this on the heating load is shown here:
Not surprisingly, the burden on the primary heating system is significantly reduced when 63 degree air is introduced versus 8 degree air. What is not represented here is the energy and equipment needed to pretreat the air to 63 degrees. A dedicated outdoor air system (DOAS) has been recommended as it is specifically designed for this functionality. A DOAS will have additional upfront, maintenance and operating costs, so this data is not all savings. A further and more in-depth analysis will be included here later.
Building glass is called “fenestration” and consists of the glass doors and windows of any structure. The glass-to-wall ratio for the Duplicable City Center was designed to be well balanced and significantly more sustainable than what is seen in many geodesic dome structures. The International Energy Code Table C303.1.3 lists default values for window specifications given their physical characteristics. The Baseline building was modeled using metal frame, clear, double glazed glass (U=0.8, SHGC=0.7).
Since the time of this writing, exact windows have not been specified, Efficient Windows Collaborative’s window selection tool was used to select windows with the following U=0.22 and SHGC=0.25.
As expected, more efficient windows greatly reduce the heat loss of the building to the outdoors.
The final variable used in the Baseline vs High-efficiency building comparison is lighting. As stated earlier, there are a multitude of benefits over and above HVAC equipment sizing when selecting more energy efficient light bulbs. You can read more about this on the One Community Lighting Analysis open source hub. Since lighting adds heat to the building, inefficiency in lighting burdens the HVAC systems during building cooling. Below is a comparison on the energy usage for cooling with baseline lighting as dictated in ASHRAE Fundamentals Chapter 18 Table 2 for the various spaces versus the high-efficiency building which uses low-wattage high-efficiency bulbs:
What you see above is the significant savings for the cooling load by using LED low-wattage bulbs versus traditional ASHRAE design standards.
So which do we recommend implementing? ALL design changes are highly recommended. In this image you can see the difference in HVAC loads when all of the above high-efficiency options are applied together.
These charts give a representation of the burden each factor places on the system in non-energy-efficient (Baseline) models and High Efficiency Models.
Tempering the outside air has the largest impact (and is most likely required by local building codes), but all factors show measurable and viable improvements. Implementation of all options significantly reduces total system requirements and creates a much more balanced load usage from the individual components. This saves resources, reduces equipment costs, and provides a more comfortable and consistent living experience for users.