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content/articles/2023-09-19-calculate-seer-degradation-by-age.md
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---
tags: formulas, HVAC, tech-tip
---
# Calculate SEER Degradation by Age
This is a quick tech-tip to learn how to calculate the degradation of SEER based
on age.
This is a quick tech-tip to learn how to calculate the degradation of SEER based on age.
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 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 tested.
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
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
tested.
## Formula
This is the formula used to calculate the SEER based on age of the evaporator
coil / air handler.
This is the formula used to calculate the SEER based on age of the evaporator coil / air handler.
$$ SEER_d = SEER_n \times (1 - M)^{age} $$
| Where | |
| -------- | ------------------------------------------ | --- |
| $SEER_d$ | Degradated SEER rating |
| $SEER_n$ | Nominal SEER rating when equipment was new |  |
| M | Maintenance factor, 0.01-0.03 |
| age | The age of the equipment, in years |
| Where | |
| ---------- | ------------------------------------------ |
| $ SEER_d $ | Degradated SEER rating |
| $ SEER_n $ | Nominal SEER rating when equipment was new |
| $ M $ | Maintenance factor, 0.01-0.03 |
| $ age $ | The age of the equipment, in years |
The maintenance factor of 0.01 is for expertly maintained equipment and 0.03 is
for unmaintained. The maintenance factor in essence is based on 1%-3%
degradation per year, however there are some
[studies](https://publications.energyresearch.ucf.edu/wp-content/uploads/2018/09/FSEC-PF-474-18.pdf)
that show that this can actually be as 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 would be.
The maintenance factor of 0.01 is for expertly maintained equipment and 0.03 is for unmaintained. The maintenance factor in essence is based
on 1%-3% degradation per year, however there are some
[studies](https://publications.energyresearch.ucf.edu/wp-content/uploads/2018/09/FSEC-PF-474-18.pdf) that show that this can actually be as
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
would be.
Interestingly, the study linked also shows that the degradation is higher the
higher the tonnage of the equipment. It also shows that the degradation is lower
per year the higher the nominal SEER rating of the system (which is corelated to
using TXV's and lower airflow rates because of the equipment having multiple
stages).
Interestingly, the study linked also shows that the degradation is higher the higher the tonnage of the equipment. It also shows that the
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
because of the equipment having multiple stages.
## Example
Let's consider that we have a 13 SEER piece of equipment that was matched when
installed and the system is 15 years old.
Let's consider that we have a 13 SEER piece of equipment that was matched when installed and the system is 15 years old.
Plugging those numbers into our formula.
@@ -54,14 +47,13 @@ $$ SEER_d = 13 \times (1 - 0.01)^{15} = 11.2 $$
---
#### Highest Rage (5% degradation / year)
#### Highest Range (5% degradation / year)
$$ SEER_d = 13 \times (1 - 0.05)^{15} = 6 $$
---
An expertly maintained system may not have degraded that much, with an 11.2 SEER
vs. a poorly maintained / dirty system that also suffers from refrigerant charge
losses can be as low as 6 SEER.
An expertly maintained system may not have degraded that much, with an 11.2 SEER vs. a poorly maintained / dirty system that also suffers
from refrigerant charge losses can be as low as 6 SEER.
Thanks for learning how to estimate SEER degradation based on equipment age!