Functional requirements are necessary product features that users must implement in order to accomplish their tasks. They define fundamental system behavior and operational specifications.
The functional requirements have been updated and are organized into five major requirements with each major requirement having sub-requirements. The team felt this update was needed after listening to feedback from professors who suggested limiting the amount of main functional requirements and going into depth on the remaining main functional requirements. The remaining five main functional requirements identified by our stakeholders include: Thermal Storage, Testing, Financial Justification, Safety and Legality, and Localized Comfort Functions. The visit with Easton Housing Authorities to the Buskhill Lot helped to identify financial justification and payback periods as a requirement as well as localized comfort function. Kate Yoder from TRANE in her interview revealed the importance of testing, thermal storage, and safety and legal implications. HVAC contractors from Hannaberry moreover reinforced the importance of testing, safety and legality, as well as localized thermal comfort as functional requirements. Finally, the Bushkill House visit and survey of homeowners emphasized the importance of financial justifications of the system being a major functional requirement. Functional requirements that the team deemed too complex to achieve in only one semester of prototyping were added to a new category called “Future Functional Requirements.”
All of the above requirements were expanded on through literature review. Sources and justification for them can be seen below the table.
Sources for Functional Requirements Table:
1.1) This functional requirement states the constraint for the minimum efficiency requirement for the system. This constraint is based on similar HVAC system requirements.
Sources:
[1.1a] “Types of cooling systems,” Types of Cooling Systems | Smarter House. [Online].
Available: https://smarterhouse.org/cooling-systems/types-cooling-systems. [Accessed:
07-Nov-2022].
[1.1b] J. R. Turpin, “Prepare now for 2023 energy efficiency standards,” ACHR News RSS, 21-May-2022. [Online]. Available: https://www.achrnews.com/articles/146585-prepare-now-for-2023-energy-efficiency-standards#:~:text=The%20EnergyGuide%20labels%20must%20be,the%20new%202023%20SEER%20minimums. [Accessed: 17-Nov-2022].
1.2) This functional requirement describes the needed thermal storage capacity to have resilience during power outages and unforeseen blackouts. It is assumed that there is enough backup power available to run the system’s fans but not the compressor. Data was gathered from the Building Energy Codes Program from the Office of Energy Efficiency and Renewable Energy [1.2d].The storage calculations were made according to the Woodroof’s [1.2b] methods. Context for PCM calculations, mini-split systems, and storage calculations came from [1.2a, 1.2c, 1.2d].
Sources:
[1.2a] Author(s) Carter, Author(s) Florida Solar Energy Center, Author(s) Pacific Northwest
National Laboratory, Author(s) Air Conditioning Contractors of America, Author(s) Burdick,
Author(s) EIA, Author(s)
Gilbride, Author(s) Karr, Author(s) NEEA, Author(s) RESNET, Author(s) Air-Conditioning
Heating and Refrigeration Institute, Author(s) U.S. Department of Energy, Author(s) Natural
Resources Canada, and
Author(s) BetterBuilt NW, “Mini-split (ductless) heat pumps,” Mini-Split (Ductless) Heat
Pumps | Building America Solution Center. [Online]. Available:
https://basc.pnnl.gov/resource-guides/mini-split-ductless-heat-pumps#edit-group-scope.
[Accessed: 03-Nov-2022].
[1.2b] E. A. Woodroof, “Part II: How to do Thermal Energy Storage.” Buildings Magazine,
Jan-2015.
[1.2c] “PHASE CHANGE MATERIAL (PCM) SELECTION,” Advance Cooling Technologies.
[Online]. Available: https://www.1-act.com/products/pcm-heat-sinks/pcmselection/.
[Accessed: 03-Nov-2022].
[1.2d] “Prototype building models,” Building Energy Codes Program. [Online]. Available:
https://www.energycodes.gov/prototype-building-models#Residential. [Accessed:
03-Nov-2022].
1.2.1) This functional requirement supports the idea that energy consumption should be shifted to off peak times so the grid will be strained less. The peak power consumption time period on the grid is between 12pm and 8pm on weekdays, and the least strain on the grid is between 12am and 6am on weekdays. With the capability of shifting the load to off peak time the system will also be resilient, since it can operate when power is not available to the home during power outages. Specifically, this functional requirement sets the upper limit of what we want to achieve. This upper limit was determined by research into peak load times and power outage durations.
Sources:
[1.2.1a] A. 28, A. Yuksel, Aytek Yuksel Aytek Yuksel is the Content Marketing Leader for Cummins Inc., O. 19, Cummins Inc., Cummins Inc. Cummins, S. 13, A. 26, and A. 08, “10 U.S. states with the longest
power outages,” Cummins Inc.[Online]. Available:
https://www.cummins.com/news/2019/08/28/10-us-states-longest-power-outages.
[Accessed: 24-Oct-2022].
[1.2.1b] An exelon company,” PECO. [Online]. Available:
https://www.peco.com/SmartEnergy/InnovationTechnology/Pages/TimeOfUsePricing.aspx.
[Accessed: 24-Oct-2022].
1.2.2) This functional requirement supports the idea that energy consumption should be shifted to off peak times so the grid will be strained less. The peak power consumption time period on the grid is between 12pm and 8pm on weekdays and homes in the United States typically don’t experience power outages over 4 hours. With the capability of shifting the load to off peak time the system will also be resilient, since it can operate when power is not available to the home during power outages. Specifically, this functional requirement sets the lower limit of what we want to achieve, and achieving anything below this limit will be seen as a failure of the system. This lower limit was determined by research into peak load times and power outage durations.
Sources:
[1.2.2a] “Hourly electricity consumption varies throughout the day and across seasons,”
Homepage – U.S. Energy Information Administration (EIA). [Online]. Available:
https://www.eia.gov/todayinenergy/detail.php?id=42915. [Accessed: 24-Oct-2022].
[1.2.2b] An exelon company,” PECO. [Online]. Available:
https://www.peco.com/SmartEnergy/InnovationTechnology/Pages/TimeOfUsePricing.aspx.
[Accessed: 24-Oct-2022].
1.3) Phase change materials have begun to be incorporated in HVAC systems as a way to increase system efficiency. The selection of PCM and transition temperature are made based on existing review studies of PCM in residential building cooling. Coconut oil would be a suitable option based on a review of greener phase change materials that would be a good fit for buildings [1.3a]. A system using coconut oil as PCM increased the average COP of the system by as much as 75% and operated in a range up to 40 degrees C [1.3b]
Sources:
[1.3a] O. Okogeri, “What about greener phase change materials? A review on bio based
phase change materials for thermal energy storage applications,” Redirecting. [Online].
Available:
https://doi.org/10.1016/j.ijft.2021.100081. [Accessed: 24-Oct-2022].
[1.3b] P. Panchabiksean, “Enhancement in free cooling potential through PCM based
storage system integrated with direct evaporative cooling (DEC) unit,” Redirecting. [Online].
Available:
https://doi.org/10.1016/j.energy.2017.11.117. [Accessed: 24-Oct-2022].
2.1) In our prototyping phase, it is important for our system to read accurate measurements of temperature, relative humidity, and air flow. We will be testing our system and analyzing data to come to conclusions on thermal comfort. We need to have accurate readings with low uncertainties in order for our conclusions to be justifiable. For temperature sensors, Resistance Temperature Detectors are sensors with a relatively low instrument uncertainty when compared to other temperature sensors like thermocouples.
Sources:
[2.1a] “Temperature Probes.” Omega.co.uk. Omega Engineering, n.d. https://www.omega.co.uk/temperature/z/thermocouple-rtd.html#:~:text=RTDs%20have%20typically
%20an%20accuracy,include%20linearity%2C%20repeatability%20or%20stability.
2.2) In our prototyping phase, it is important for our system to read accurate measurements of temperature, relative humidity, and air flow. We will be testing our system and analyzing data to come to conclusions on thermal comfort. We need to have accurate readings with low uncertainties in order for our conclusions to be justifiable. Capacitive humidity sensors provide accurate relative humidity readings within a large range of relative humidities with extremes being the bounds.
Sources:
[2.2b] Roveti, Denes K. “Choosing a Humidity Sensor: A Review of Three Technologies.”
FierceElectronics.com. Fierce Electronics, July 1, 2001. https://www.fierceelectronics.com/components/choosing-a-humidity-sensor-a-review-three-technologies#:~:text=The%20typical%20accuracy%20of%20an,RH%20at%20100%C2%B0C.
2.3) In our prototyping phase, it is important for our system to read accurate measurements of temperature, relative humidity, and air flow. We will be testing our system and analyzing data to come to conclusions on thermal comfort. We need to have accurate readings with low uncertainties in order for our conclusions to be justifiable. Anemometers can measure the air velocity which then can be used in conjunction with the cross sectional area of our distribution system to determine air flow rate.
Sources:
[2.3c] “A Complete Guide to Anemometers.” IE.RS-Online.com. RS, n.d.
https://ie.rs-online.com/web/generalDisplay.html?id=ideas-and-advice%2Fanemometers-guide#:~:text=How%20accurate%20is%20an%20anemometer,%2Fh%20or%20%C2%B11mph
2.4) In this prototyping phase, it is important that our system’s operation and performance can be analyzed using data. We must have ways of recording data so that conclusions about our system can be made. It will be important to use software that can easily be integrated with our system for accurate data collection.
Sources:
[2.4a] Parkinson, T., Parkinson, A., & de Dear, R. (2019). Continuous IEQ monitoring
system: Context and development. Building and Environment, 149, 15–25.
https://doi.org/10.1016/j.buildenv.2018.12.010
3.1) This functional requirement is to ensure that the user is protected from system failure and overheating. If the system is overheating without precautions to shut down, this could lead to the device catching on fire. Moreover, there is no way for the user to know if the system is overheating if it continues to function. Therefore, to ensure the safety and prevention of fire due to overheating, the system will shut down if it reaches the setpoint temperature. Moreover, the system will automatically restart after shut down in case overheating wasn’t due to system failure. If overheating continues three times, then this is an indicatioon that the overheating is due to an issue with the system, at which point the system will shut down and user be notified.
Sources:
[3.1a] “Usbr.gov.” [Online]. Available:
https://www.usbr.gov/tsc/techreferences/mands/mands-pdfs/HVACManl.pdf. [Accessed:
24-Oct-2022].
3.2) Airflow is an important component to HVAC systems
Sources:
[3.2a] “Usbr.gov.” [Online]. Available:
https://www.usbr.gov/tsc/techreferences/mands/mands-pdfs/HVACManl.pdf. [Accessed:
24-Oct-2022].
3.3) This functional requirement is used to ensure that our final product meets important and necessary codes. This will allow our product to be legally installed in homes and buildings. Homeowners will not want to buy and install our product if it does not meet important building codes and standards.
Sources:
[3.3a] (ICC), I. C. C. (n.d.). 2021 International Energy Conservation Code (IECC): ICC
Digital Codes. 2021 INTERNATIONAL ENERGY CONSERVATION CODE (IECC) | ICC
DIGITAL CODES. Retrieved
November 16, 2022, from https://codes.iccsafe.org/content/IECC2021P1/chapter-4-re-residential-energy-efficiency#IECC2021P1_RE_Ch04_SecR403
3.4) This functional requirement involves considering the sustainability of our end-manufactured product. This may involve considering durability, recyclability, production, etc. This could also be used as a major selling point, similar to the Kobo, a competitor with the Amazon Kindle. This objective can be done in the initial prototyping, and can also be optimized later for the mass-manufactured product.
Sources:
[3.4a] “Kobo Clara 2E,” Rakuten Kobo eReader Store. [Online]. Available:
https://us.kobobooks.com/products/kobo-clara-2e. [Accessed: 24-Oct-2022].
3.5) This functional requirement comes from IECC Chapter 4 Standard R403.3.3. R-Values describe the thermal conductivity of our system. Meeting this standard will also help with our energy efficiency.
Sources:
[3.5a] (ICC), I. C. C. (n.d.). 2021 International Energy Conservation Code (IECC): ICC
Digital Codes. 2021 INTERNATIONAL ENERGY CONSERVATION CODE (IECC) | ICC
DIGITAL CODES. Retrieved
November 16, 2022, from https://codes.iccsafe.org/content/IECC2021P1/chapter-4-re-residential-energy-efficiency#IECC2021P1_RE_Ch04_SecR403
3.6) This functional requirement comes from IECC Chapter 4 Standard R403.1. All controllable HVAC systems are required to have a thermostat that can control the heating or cooling of the system on a daily basis.
Sources:
[3.6a] (ICC), I. C. C. (n.d.). 2021 International Energy Conservation Code (IECC): ICC
Digital Codes. 2021 INTERNATIONAL ENERGY CONSERVATION CODE (IECC) | ICC
DIGITAL CODES. Retrieved
November 16, 2022, from https://codes.iccsafe.org/content/IECC2021P1/chapter-4-re-residential-energy-efficiency#IECC2021P1_RE_Ch04_SecR403
3.7) This functional requirement comes from IECC Chapter 4 Standard R403.3.6. This standard focuses on duct leakage. This code will help us ensure that we are energy efficient and not leaking too much air out of our ducts.
Sources:
[3.7a] (ICC), I. C. C. (n.d.). 2021 International Energy Conservation Code (IECC): ICC
Digital Codes. 2021 INTERNATIONAL ENERGY CONSERVATION CODE (IECC) | ICC
DIGITAL CODES. Retrieved
November 16, 2022, from https://codes.iccsafe.org/content/IECC2021P1/chapter-4-re-residential-energy-efficiency#IECC2021P1_RE_Ch04_SecR403
4.1) The payback period is an important part of the financial aspect of the project. We know that homeowners on average stay in their homes for about 13 years. We want our payback period to significantly less than 13 years so that homeowners can get clear benefits from buying our product. Furthermore, five years seems to be realistic based on payback periods of similar HVAC systems in the market. Our prototype may cost more than our final product so we will have to take that into account when we calculate the payback period from the prototype.
Sources:
[4.1a] Tobias, M. (2021, June 15). How to finance building upgrades: Using a blended
payback period. MEP Engineering & Design Consulting Firm. Retrieved November 16, 2022, from https://www.ny-engineers.com/blog/financing-building-upgrades-blended-payback-period#:~:text=Major%20HVAC%20upgrades%2C%20renewable%20generation,7%2D8%20years%20on%20average.
4.2) This functional requirement constrains us to stay within the allotted budget we are given by the mechanical engineering department.
4.3) The functional requirement of using locally commercially available components will ensure our prototype as a whole will be affordable to our potential consumers. Mass production of these parts allows companies to sell individual units for lower prices [4.3a]. Since retailer prices are relatively affordable to consumers, by using parts from such stores, our overall prototype will fulfill our objective of being cost effective and will work up to an affordable mass produced prototype.
Sources:
[4.3a] P. Boyce. “Mass Production Definition.” BoyceWire. [Online]. Available:
https://boycewire.com/mass-production-definition/. [Accessed: 3-Nov-2022].
5.1) This functional requirement was based on the fact that existing zoning panels can control up to four zones and if more than four zones are required, additional zoning panels can be installed. In order to be competitive with existing systems, our device should allow for control of at least four zones from a singular panel/location.
Sources:
[5.1a] “What Is an HVAC Zoning System? (And Why It Works).” Fire & Ice,
https://indoortemp.com/resources/what-is-hvac-zoning-system. Accessed 7 Nov. 2022.
5.2) This functional requirement is based on the average operating noise of residential HVAC systems
Sources:
[5.2a] : “How Loud is a Decibel? Why Quiet Appliances Make a Difference,” Trane,
3-May-2022. [Online].
Available:
https://www.trane.com/residential/en/resources/blog/loud-decibel-quiet-appliances-make-difference/. [Accessed: 3-Nov-2022].
5.3) This functional requirement pertains to the team’s goal of providing a system that maintains thermal comfort throughout the entire year. Since the team’s goal is to provide sensible temperature control and not humidity control, research was focused on the sensible temperature ranges that humans are most comfortable with depending on the weather and activity levels.
Sources:
[5.3a] “Indoor Environmental Quality: HVAC management,” Centers for Disease Control
and Prevention, 25-Feb-2022. [Online]. Available:
https://www.cdc.gov/niosh/topics/indoorenv/hvac.html. [Accessed:24-Oct-2022].
[5.3b] Chapter 10B: The Psychrometric Chart (updated 7/22/2014). [Online]. Available:
https://www.ohio.edu/mechanical/thermo/Applied/Chapt.7_11/Chapter10b.html. [Accessed:
24-Oct-2022].
[5.3c] Cielo, “The ideal room temperature for every situation & 7 ways to maintain it!,” Smart
AC Controller, 07-Mar-2022. [Online]. Available: https://www.cielowigle.com/blog/ideal-room-temperature/.[Accessed: 24-Oct-2022].
Sources for Future Functional Requirements Table:
- Thermal energy storage is important and can work on various time scales. Thermochemical storage can provide the ability to store heat for weeks and maybe even a few months with zero heat lost. Our priority is thermal comfort and keeping the home warm per day, but in the future, this project could be expanded to cover seasonal energy storage and keeping the home warm during the winter. In the future, this project could prioritize the length of time for which thermal energy should be able to be stored and allow for up to 5% of heat loss.
Sources:
[1a] “Storing Summer Heat to Use in Winter.” EurekAlert!,
https://www.eurekalert.org/news-releases/945013. [Accessed 7-Nov-2022]. - The need to make sure our control operation of our solution can be properly used by people with a range of physical and cognitive abilities stems from the fact that 1 in 5 people are over the age of 65 in many industrial countries and as people age, vision, hearing, balance, coordination, and memory are susceptible to gradual change from when they were younger. When designing to accommodate older adults, it also promotes simplicity, flexibility and ease of use for people of any age and ability. The design principles found in [2a] consider the sensory functions, mobility, and cognition of older adults which promote simplicity and equity for people with a range of abilities, irrespective of age.
Sources:
[2b] S. Polyuk, “A guide to interface design for older adults,” Toptal Design Blog,
20-Jun-2019. [Online]. Available:
https://www.toptal.com/designers/ui/ui-design-for-older-adults. [Accessed: 24-Oct-2022]. [2a] M. A. Farage, K. W. Miller, F. Ajayi, and D. Hutchins, “Design principles to
accommodate older adults,” Global journal of health science, 29-Feb-2012.
[Online]. Available:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4777049/. [Accessed: 24-Oct-2022].
- This functional requirement states the necessity of the new system to be compatible with existing systems for integration and easily installed.
Sources:
[3a] “Integrated Thermal Energy Storage System for air-conditioners with …” [Online].
Available: https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=3115&context=iracc.
[Accessed: 03-Nov-2022].
- The average time that individuals live in their home, depending on the city, is between 6.8 to 16.7 years. The average home tenure for 2021 in total was 13.2 years.
Sources:
[4b] D. Anderson, “The Typical U.S. Home Changes Hands Every 13.2 Years,” Redin News, 2-Mar-2022. [Online]. Available: https://www.redfin.com/news/2021-homeowner-tenure/. [Accessed: 3-Nov-2022]. [4a] D. Anderson, “The Typical U.S. Home Changes Hands Every 13.2 Years,” Redin
News, 2-Mar-2022. [Online]. Available:
https://www.redfin.com/news/2021-homeowner-tenure/. [Accessed: 3-Nov-2022].
- This requirement outlines the physical size of the system. At this stage of the project, we are still unsure if this system will go inside or outside. This may affect the size since if the system is outside this may allow it to have increased size and capacity due to the greater availability of space. However, keeping the system inside and/or keeping it small may make the home more aesthetically welcoming. Other than that, the general assumption for now is that this system will have a size comparable to that of a water heater or generator.
Sources:
[5a] “Amazon.com: WEN 56475 4750-watt portable generator with electric start …” [Online].
Available:
https://www.amazon.com/WEN-56475-4750-Watt-Generator-Compliant/dp/B00IUKKMDC.
[Accessed:24-Oct-2022].
[5b] I. Generac Power Systems, “Powering your home, your business, your world.,”
Generac Power Systems Backup Power for Your Home with Generac Home Generators.
[Online]. Available:
https://www.generac.com/for-homeowners/home-backup-power. [Accessed: 24-Oct-2022].
[5c] S. G. I. [www.searchgurus.ca], “Power generator specifications – serving all of Ontario
including Toronto, Mississauga and the GTA.,” Emergency Diesel Power Generator Rental
Company. [Online].
Available: https://www.lmgenpower.com/genspecs.php . [Accessed: 24-Oct-2022].
[5d] S. Stone, “Water heater dimensions: Finding the right water heater for a tight space,”
Water Heater Leaking Info, 08-Jul-2021. [Online]. Available:
https://www.waterheaterleakinginfo.com/water-heater-dimensions/ . [Accessed:
24-Oct-2022].