Our criteria matrix consisted of 16 criteria fully described in the Criteria For System Selection section of this site. These criteria were all selected to analyze HVAC systems for a Whole Foods demonstration kitchen. All of these criteria were assigned a rating on a scale of 1-5, with 5 indicating a superior efficiency in the given criteria. Each criteria has different ratings depending on the location of the building. For example, a natural ventilation system in Anchorage Alaska would have a much lower rating than a system in a less harsh environment. Once these values were assigned based on research into each system, the location and size factors needed to be implemented. Our excel worksheet for our criteria matrix can be found here: CriteriaMatrixFinal
From this point, the above criteria matrix was created using Microsoft Excel. We based our design off of a couple prior criteria matrices from the fall term AE-390 students of 2011. The links to their websites can be found in the References section of this website. Our basic design consisted of a final output sheet, and individual sheets for criteria based on location. Each location and building size can have a great affect on the individual criteria. We assigned ratings of 1-5 to how much the location and size of the building affect each criteria. These values were then multiplied with the original ratings or each criteria. Below is the formula used to calculate the values prior to owner weighting for each criteria.
In this case, we are looking at the maintenance cost criteria of a VAV system for a demonstration kitchen in New York. The criteria rating in the first table is multiplied by the location and size rating in the second table to get a score that can be later weighted by the owner’s conditions. In order to factor in that multiple sizes can be selected, a CHOOSE function is implemented. This decides which size rating to use in the equation based off of the owner’s intended size selection on the final output.
Once this initial score has been determined, the final output page can be used to determine the weight of each criteria depending on the owner’s indented construction and requirements. The final output sheet shown at the top of this page takes the location and size weighted values from each location sheet and adds a weighted factor decided by the owner and engineer for each criteria. The owner and engineer can decide the level of importance of each criteria ranging from not important to very important. Below is the formula used to get the final score typically ranging from 1-75 for each criteria. There are 3 criteria however, that can exceed 75; environmental impact, efficiency, and sustainability. This is due to the multiplying of the total rating by 1.5 in these criteria based on the assumption that Whole Foods will want to use Green technology.
Once all the values were found for all the criteria, the cumulative rating value can be found by summing all the ratings. This number is then converted into a percentage based off the total possible rating of 1200 pts indicating a perfect HVAC solution. This total number does not include the extra points assigned for Green technology in the 3 criteria previously discussed. Since no solution is going to be perfect, these percentages are typically in the mid to low percentile range. Once these percentages are found, a simple RANK function was added to make it clear which system scored the highest in the matrix. Ultimately this is the best overall solution, however, there can often be other solutions that are very close in percentile that are viable options as well.
In order to control certain systems that upon initial inspection would simply not be a viable option at a certain location, limiting IF statements were implemented in the final sum. Below is one example of a limiting factor, in this case for the DOAS/Radiant Cooling option.
This equation simply states that if the demonstration kitchen is in New York, Anchorage, or Milwaukee, that the DOAS/Radiant Cooling sum should be multiplied by zero. This ensures that this system is not selected for these locations due to the fact that heating is not a primary part of the system. These locations are all drop to very low temperature, as would most likely have high heating loads for large portions of the year. A cooling system would not be adequate for these locations and an additional system would need to be implemented for heating.
Using this matrix to determine the proper HVAC system for a Whole Foods demonstration kitchen, we found that the VAV system was the best overall solution for the majority of the given conditions. VAV offers high heating and cooling capacity while having excellent exhaust and ventilation capabilities. Being that our location is a kitchen, exhaust is crucial in ensuring proper air conditions with the plethora of heavy cooking equipment. Being a kitchen, there are also many particulates and gases that need to be address in order to ensure a clean environment. Due to the variability of air volume, the system also is very efficient all around. This is important since the space will not be used often however when used, the loads are extreme. This infrequent use combined with large loads demands a system that can vary airflow and volume.
Knowing that Whole Foods is the owner, green energy solutions were also a major part of the selection process. As previously discussed; the efficiency, environmental impact, and sustainability were all multiplied by a 1.5 factor. While this did increased VAV’s chances, it also made some Green methods look much more desirable. This helps with the decision process overall. After the matrix gives the best answer based on all criteria, the owner can than decide if there are systems that are very close in ranking, that they would rather go with a Green option that might be ranked at 2 or 3. This is one of the many ways that this criteria matrix is dynamic and a good decision tool for the owner and designer to come up with the most appropriate HVAC system.
HVAC Selection 