The single most important metric of any portable air conditioner is capacity. This denotes how powerful a portable AC unit is. The problem arises when we see 2 different numbers for capacity:
- BTU ASHRAE. These are British Thermal Units, measured by the American Society of Heating, Refrigeration, and Air Conditioning Engineers. This is the old standard we understand quite well. Measurement temperature: 80°F.
- BTU DOE or SACC/CEC. SACC stands for Seasonally Adjusted Cooling Capacity and it’s measured by the Department Of Energy DOE. This is the new standard from October 1 2017 10 CFR Parts 429 and 430 DOE portable air conditioner standards we are usually not familiar with. Measurement temperatures: 83°F and 95°F.
In short, we have two standards for measuring portable AC capacity. That’s why we get a lot of questions about BTU SACC vs ASHRAE because a 14,000 BTU portable AC is now rated as 10,000 BTU unit, for example.
Note: BTU SACC rating is always lower than the BTU ASHRAE rating (this has to do with the weighted average at various test conditions; SACC BTUs are usually about 25% to 45% lower than ASHRAE BTUs). This is the SACC formula we explain further on:
SACC = (ACC95 × 0.2) + (ACC83 × 0.8)
Prior to October 1, 2017, you would only see BTU ASHRAE metric. Now, if you open a specification sheet of any portable air conditioner, you can BTU ASHRAE rating as well as SACC BTU rating. We are going to explain why this is and how to navigate SACC vs ASHRAE capacity ratings.
To illustrate the confusion this ASHRAE vs SACCC capacity measurements make, let’s look at an example of a unit with both BTU ASHRAE and BTU SACC rating.
Example Of BTU SACC VS ASHRAE Portable Air Conditioner (BLACK+DECKER BPP10WTB)
We will look at one of the most popular air conditioners on the market. This is the BLACK+DECKER BPP10WTB 14,000 BTU air conditioner. From the screenshot below, you can see that we can choose between two units:
- BLACK+DECKER 10,000 BTU SACC/CEC (14,000 BTU ASHRAE).
- BLACK+DECKER 7,700 BTU SACC/CEC (14,000 BTU ASHRAE).
Both of these are conditioners are 14,000 BTU air conditioners. Why do they have a different BTU DOE (also known as BTU SACC) rating? Namely 7,700 BTU SACC vs 10,000 BTU SACC.
14,000 BTU air conditioner should be a 14,000 BTU air conditioner. Right? Not exactly. If you check the specified coverage area – what size rooms each of these portable AC units can adequately cool – you see a difference as well (despite both of them having the same 14,000 BTU ASHRAE rating):
This is quite confusing. How come the 1st 14,000 BTU portable AC unit can cool rooms up to 350 sq ft while the 2nd 14,000 BTU portable AC unit can cool rooms up to 450 sq ft?
Obviously, the difference is due to different BTU SACC capacity rating. If you compare both units and both capacity ratings, we have:
- BTU ASHRAE rating: 14,000 BTU vs 14,000 BTU. Both of these portable AC units seem to have the same cooling output.
- BTU CACC rating: 7,700 BTU vs 10,000 BTU. We see the difference here. Unlike the BTU ASHRAE rating, these BTU CACC ratings are different. 10,000 BTU unit has a 29% higher cooling capacity than the 7,700 BTU unit. 450 sq ft cooling coverage is also 29% bigger than 350 sq ft cooling coverage.
As we can see, ASHRAE vs SACC BTU rating is quite puzzling. In order for us to understand how powerful portable AC unit we’re looking at, we have to look into exactly what BTU ASHRAE and BTU CACC mean:
BTU ASHRAE Vs BTU SACC Explained
According to the FTC (Federal Trade Commission) rules, all new portable air conditioners have to have specified BTU ASHRAE and BTU DOE SACC capacities.
How ASHRAE Measures Portable AC Capacity (BTU ASHRAE)
As you can read in a section for air conditioning on ASHRAE, the BTU ASHRAE capacity is quite simple to understand. We get the capacity in BTU at specified test conditions, outlined by ANSI/AHAM PAC-1-2009.
Here are the ASHRAE BTU test conditions for portable air conditioners:
- Dry-bulb temperature of 80°F.
- Wet-bulb temperature of 67°F. This corresponds to 51% relative humidity.
These bulb temperatures might sound complex a bit. The methodology of how ASHRAE tests out portable AC units is outlined in ANSI/ASHRAE Standard 16-1983 (RA 99), “Method of Testing for Rating Room Air Conditioners and Packaged Terminal Air Conditioners”.
The bottom line is that ASHRAE test all portable air conditioners at specified test conditions. These are usually ideal conditions for portable AC unit performance. We get the familiar BTU ASHRAE capacity. That is the 14,000 BTU in our example above.
Now, when we use a portable AC unit, the conditions are not always perfect. We may use the unit at 75°F, 80°F, 90°F, 100°F, 120°F and so on. The relative humidity can also differ from 51%. You can use a portable AC unit at 40%, 60%, 75%, 90% relative humidity, and so on.
Obviously, the performance – cooling capacity portable AC unit can output – changes when we change the temperature and relative humidity.
In order to best evaluate how powerful a portable AC is under these various conditions, DOE went ahead and created a new rating SACC/CAC rating for portable AC units:
How DOE Measures Portable AC Capacity (BTU SACC Or BTU DOE Rating)
On October 1, 2017, DOE introduced a new BTU SACC rating for portable AC units (10 CFR Parts 429 and 430, “Energy Conservation Program: Energy Conservation Standards for Portable Air Conditioners”).
The goal here was to evaluate the performance of PACs under various conditions we face during the summer. If you compare BTU ASHRAE vs BTU DOE, the ASHRAE value is not able to account for these changing conditions; BTU DOE can account for them.
BTU SACC rating or Seasonally Adjusted Cooling Capacity rating measures the performance of portable AC units in BTU/h at more real-like conditions. In practice, this is a weighted average of performance at various temperatures and relative humidity levels. On top of that, BTU DOE also accounts for the impacts of infiltration air for single-hose portable air conditioners.
According to the new DOE standard, BTU SACC is calculated using this formula:
SACC = (ACC95 × 0.2) + (ACC83 × 0.8)
ACC95 is an adjusted cooling capacity at 95°F dry-bulb temperature, weighted by a 0.2 weighting factor.
ACC83 is an adjusted cooling capacity at 83°F dry-bulb temperature, weighted by a 0.8 weighting factor.
BTU ASHRAE rating only considers 1 condition (80°F dry-bulb, 67°F wet-bulb). In contrast, the BTU SACC rating considers 2 conditions (95°F dry-bulb and 83°F dry-bulb) while also using the weighted average (0.2 and 0.8 weighted factors) to account for other real-life conditions.
Now, given that we have different test conditions for measuring BTU DOE vs BTU ASHRAE, we can’t directly convert DOE to ASHRAE. The best we can do is set up rough estimates on how the old BTU ASHRAE metric can be converted into the new BTU DOE metric for cooling output:
Converting BTU ASHRAE To BTU DOE
As stated before, the new BTU DOE rating is usually anywhere from 25% to 45% lower than the older BTU ASHRAE rating. To give you an idea of what the new rating should be (based on the old rating), we have created a conversion table from BTU ASHRAE to BTU DOE using the median 35% difference (rounded up to 100 BTU).
This will illustrate how to convert from the old BTU ASHRAE rating to the new DOE BTU SACC rating. Here is the full chart, along with the coverage area:
|Old ASHRAE BTU||New DOE BTU SACC||Coverage Area:|
|8,000 BTU ASHRAE||5,200 BTU DOE||Up To 250 Sq Ft|
|9,000 BTU ASHRAE||5,900 BTU DOE||Up To 300 Sq Ft|
|10,000 BTU ASHRAE||6,500 BTU DOE||Up To 350 Sq Ft|
|11,000 BTU ASHRAE||7,200 BTU DOE||Up To 400 Sq Ft|
|12,000 BTU ASHRAE||7,800 BTU DOE||Up To 450 Sq Ft|
|13,000 BTU ASHRAE||8,500 BTU DOE||Up To 500 Sq Ft|
|14,000 BTU ASHRAE||9,100 BTU DOE||Up To 600 Sq Ft|
Example: Let’s say that you are looking at a 14,000 BTU ASHRAE portable air conditioner. How many new BTU DOE should it be rated? Depending on how efficient it is at higher temperatures, it should be rated anywhere from 7,700 BTU DOE to 10,500 BTU DOE.
Bottomline On ASHRAE Vs DOE BTU Ratings
In theory, the new DOE BTU rating (SACC) should be better at telling us how powerful a portable AC unit is in real-time conditions. Due to its complexity, however, it might take some time for DOE BTU rating to take over the old ASHRAE BTU standard.
In practice, however, most HVAC experts still use the old ASHRAE BTU standard as the benchmark for portable AC performance. When trying to figure out what size air conditioner you need (here’s a helpful calculator), the old ASHRAE BTU rating is used more often than the new SACC BTU rating.
In the same document that DOE introduced the SACC BTU rating for portable air conditioner capacity, they have also introduced the CEER rating. CEER is an energy efficiency rating, in the same metrics family as EER and SEER ratings. You can read more about CEER rating here.
Based on both of these metrics and several other factors, we have also made a list of the best and most energy efficient portable air conditioners (you can check it here).
Hopefully, now you understand more thoroughly why there are two BTU ratings in the portable air conditioners.
2 thoughts on “Explained: DOE BTU SACC Vs ASHRAE In Portable AC Units”
This still doesn’t explain how 2 different machines with the same ashrae rating can have different doe ratings. Can you explain that please?
Hi R. Trotter, well, we need to be aware that different portable AC units have different efficiencies at different temperatures. The BTU ASHRAE measures that efficiency (and the resulting BTU output) at 80°F. 2 different units can have the same BTU ASHRAE; but, if they have a different temperature-efficiency relationship, the BTU DOE rating will be different.
Example: We have two 14,000 BTU ASHRAE units (that’s the cooling output at 80°F). Now, the 1st unit will be much less efficient higher than 80°F temperature. The resulting BTU DOE output (as measured at 83°F and 95°F, and calculated with 80% and 20% weights) will be lets say 8,000 BTU DOE. The 2nd unit, however, can sustain a higher efficiency even at higher temperatures (above 80°F, specifically at 83°F and 95°F). This 2nd unit will thus have a higher BTU DOE rating (let’s say 10,000 BTU) despite both of them having the same BTU ASHRAE rating at 80°F.
Hope this makes things a bit clearer.