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mhoush: Calculate SEER Degradation by Age
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<meta content="This is a quick tech-tip to learn how to calculate the degradation of SEER based
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on age.
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The degradation of SEER is due to fouling of the evaporator coil with dirt and
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refrigerant charge losses. It should be noted that this is not true for..." name="description"/>
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<meta content="This is a quick tech-tip to learn how to calculate the degradation of SEER based
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on age.
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The degradation of SEER is due to fouling of the evaporator coil with dirt and
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refrigerant charge losses. It should be noted that this is not true for..." name="og:description"/>
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<h1>
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Calculate SEER Degradation by Age
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</h1>
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<div class="-mt-6">
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<div class="text-gray gray-links text-sm">
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<span class="border-r border-gray pr-2 mr-2">September 19, 2023</span>395 words, posted in <a href="/articles/tag/hvac/">HVAC</a>, <a href="/articles/tag/formulas/">formulas</a> and <a href="/articles/tag/tech-tip/">tech-tip</a>
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<img alt="banner" src="http://localhost:3000/articles/images/2023-09-19-calculate-seer-degradation-by-age.png"/>
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<p>This is a quick tech-tip to learn how to calculate the degradation of SEER based
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on age.</p>
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<p>The degradation of SEER is due to fouling of the evaporator coil with dirt and
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refrigerant charge losses. It should be noted that this is not true for all
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applications, but is used as an estimation based on research done by the <code>DOE</code>
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of the average degradation based on systems tested.</p>
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<h2>Formula</h2>
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<p>This is the formula used to calculate the SEER based on age of the evaporator
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coil / air handler.</p>
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<p>$$ SEER_d = SEER_n \times (1 - M)^{age} $$</p>
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<p>| Where | |
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| –––– | —————————————— | — |
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| $SEER_d$ | Degradated SEER rating |
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| $SEER_n$ | Nominal SEER rating when equipment was new | |
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| M | Maintenance factor, 0.01-0.03 |
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| age | The age of the equipment, in years |</p>
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<p>The maintenance factor of 0.01 is for expertly maintained equipment and 0.03 is
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for unmaintained. The maintenance factor in essence is based on 1%-3%
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degradation per year, however there are some
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<a href="https://publications.energyresearch.ucf.edu/wp-content/uploads/2018/09/FSEC-PF-474-18.pdf">studies</a>
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that show that this can actually be as high as 5% or above depending on climate.
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We could use up to 0.05 as the maintenance factor, just to see what the “range”
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of degradation would be.</p>
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<p>Interestingly, the study linked also shows that the degradation is higher the
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higher the tonnage of the equipment. It also shows that the degradation is lower
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per year the higher the nominal SEER rating of the system (which is corelated to
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using TXV’s and lower airflow rates because of the equipment having multiple
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stages).</p>
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<h2>Example</h2>
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<p>Let’s consider that we have a 13 SEER piece of equipment that was matched when
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installed and the system is 15 years old.</p>
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<p>Plugging those numbers into our formula.</p>
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<hr />
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<h4>Lowest Range (1% degradation / year)</h4>
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<p>$$ SEER_d = 13 \times (1 - 0.01)^{15} = 11.2 $$</p>
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<hr />
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<h4>Highest Rage (5% degradation / year)</h4>
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<p>$$ SEER_d = 13 \times (1 - 0.05)^{15} = 6 $$</p>
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<hr />
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<p>An expertly maintained system may not have degraded that much, with an 11.2 SEER
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vs. a poorly maintained / dirty system that also suffers from refrigerant charge
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losses can be as low as 6 SEER.</p>
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<p>Thanks for learning how to estimate SEER degradation based on equipment age!</p>
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</article>
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Written by
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<h3 class="!m-0">
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Michael Housh
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</h3>
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<p class="text-gray">
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HVAC business owner with over 27 years of experience. Writes articles about HVAC,
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Programming, Home-Performance, and Building Science
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More articles
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<a class="[&:hover]:border-b border-orange" href="/articles/2025/vapor-htmx-todo-app/">Vapor + HTMX</a>
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<h2 class="text-2xl font-bold mb-2">
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<a class="[&:hover]:border-b border-orange" href="/articles/2024/free-as-in-freedom/">Free As In Freedom</a>
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<div class="text-gray gray-links text-sm mb-4">
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<span class="border-r border-gray pr-2 mr-2">April 09, 2024</span><a href="/articles/tag/general/">general</a>, <a href="/articles/tag/open-source/">open-source</a> and <a href="/articles/tag/software/">software</a>
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Salute to open-source software engineers
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