60 lines
2.4 KiB
Markdown
60 lines
2.4 KiB
Markdown
---
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tags: formulas, HVAC, tech-tip
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---
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# Calculate SEER Degradation by Age
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This is a quick tech-tip to learn how to calculate the degradation of SEER based on age.
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The degradation of SEER is due to fouling of the evaporator coil with dirt and refrigerant charge losses. It should be noted that this is
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not true for all applications, but is used as an estimation based on research done by the `DOE` of the average degradation based on systems
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tested.
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## Formula
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This is the formula used to calculate the SEER based on age of the evaporator coil / air handler.
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$$ SEER_d = SEER_n \times (1 - M)^{age} $$
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| 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 |
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The maintenance factor of 0.01 is for expertly maintained equipment and 0.03 is for unmaintained. The maintenance factor in essence is based
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on 1%-3% degradation per year, however there are some
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[studies](https://publications.energyresearch.ucf.edu/wp-content/uploads/2018/09/FSEC-PF-474-18.pdf) that show that this can actually be as
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high as 5% or above depending on climate. We could use up to 0.05 as the maintenance factor, just to see what the "range" of degradation
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would be.
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Interestingly, the study linked also shows that the degradation is higher the higher the tonnage of the equipment. It also shows that the
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degradation is lower per year the higher the nominal SEER rating of the system, which is correlated to using TXV's and lower airflow rates
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because of the equipment having multiple stages.
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## Example
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Let's consider that we have a 13 SEER piece of equipment that was matched when installed and the system is 15 years old.
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Plugging those numbers into our formula.
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---
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#### Lowest Range (1% degradation / year)
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$$ SEER_d = 13 \times (1 - 0.01)^{15} = 11.2 $$
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---
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#### Highest Range (5% degradation / year)
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$$ SEER_d = 13 \times (1 - 0.05)^{15} = 6 $$
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---
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An expertly maintained system may not have degraded that much, with an 11.2 SEER vs. a poorly maintained / dirty system that also suffers
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from refrigerant charge losses can be as low as 6 SEER.
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Thanks for learning how to estimate SEER degradation based on equipment age!
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