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Dual Hose Portable Air Conditioners

dual hose unit

An air conditioner cools air

How much can it cool – to what extent can it cool – its capacity to cool

is measured in BTUs/hr.

BTU stands for British thermal units.

A BTU is “defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit”

A portable air conditioner removes heat from the air it processes.

Its capacity to remove heat is measured in BTU/hr

So a 10,000 BTU/hr air conditioner essentially has the ability to remove the equivalent amount of heat from a given quantity of air that would be required to heat 1 lb. of water by one degree F one 10,000 times over in one hour.

Old Testing

Who determines whether a particular portable air conditioner has 10,000, 12,000, or 14,000 BTUs/hr of cooling capacity?

Each portable air conditioner is tested according to the current government mandates for testing.

These mandates used to be quite lax

Portable air conditioners were tested under these conditions:

  • two chambers – one with the ac, duct, window kit, etc. inside of it; the other representative of the outdoors
  • the indoor chamber was set to a rather cool ambient air temp of 80° F
  • the outdoor chamber was set to an ambient air temp of 95° F for dual hose units. No outdoor air temperature (for the second chamber) was specified for single hose units

Depending on how many British thermal units of heat a particular model portable air conditioner could remove from the air in the test chamber per hour it was given a particular BTU rating – 10,000 BTU units could remove 10,000 BTUs per hour; 12,000 BTU units could remove 12,000 BTUs per hour, etc.

Heat Transfer in AC Systems

Any air conditioner (in other words, not just portable air conditioners) cools air via three primary components:

  • Compressor – compresses refrigerant
  • Condenser – condenses refrigerant
  • Evaporator – evaporates refrigerant

Especially relevant to this discussion are the evaporator and condenser.

The evaporator is cold – it removes heat from air that travels over it – this is how an air conditioner cools air.

The condenser is hot – it adds heat to air that surrounds it.

In a central air conditioning system the hot side of the system is outdoors – the condenser is outside the house.

In a portable air conditioner the condenser is part of the whole portable system – it’s indoors along with that system.

The heat generated by the condenser has to be removed.

In a central air conditioning system outdoor air is pulled over the condenser via a large fan. The outdoor air may be hot but it’s not nearly as hot as the condenser – i.e. it’s colder than the condenser. This facilitates heat transfer from the condenser to that warm outdoor air.

In a single hose portable AC unit cooled indoor air is pulled over the condenser. This cooled air is immediately warmed up and is removed from the room via a duct that you fit into a plastic mounting bracket in your window.

Unfortunately, this removal of warmed air has two substantial side effects

  • infiltration air heat transfer (more on this in just a bit)
  • duct heat transfer

In a dual hose unit, warm outdoor air is pulled over the condenser much like it is in a central air conditioning system. However, here the outdoor air is pulled into the AC unit via a (second) duct. The outdoor air is warm but, again, its cooler than the condenser so it can still cool it. Cooling the condenser adds heat to the air and this heated up air is exhausted via an exhaust duct much the same as it is in a single hose unit.

Note that many dual hose units still intake some cooled indoor air to pull over the condenser. For example, see the small grille (below the left intake) on the back of the dual hose Whynter ARC-14S which helps facilitate this process.

intake

As such, using a dual hose unit still involves

  • infiltration air heat transfer
  • duct heat transfer

Infiltration air heat transfer

In a single hose system, the removed air (that was used to cool the condenser) creates an area of low pressure inside of the room. Comparatively, outdoor air is at a higher pressure. A pressure gradient is created between warmer outdoor air and cooled indoor air.

The cooled room is essentially pulling air into itself from outside of it to replace the air that it lost when cooling the condenser.

This outdoor air comes from multiple sources

  • surrounding rooms
  • the attic
  • outside the house

All of these sources are likely to contain air that’s much warmer than the cooled air inside the cooled room.

Thus, warm air is constantly infiltrating the room and actively working against the cooling of the room by the AC unit.

In a dual hose system, the same process occurs. The unit may not intake exactly the same amount of air from the outdoors as it exhausts. In addition, it may also intake a small portion of cooled indoor air to cool its condenser. All of this may create at least a small pressure gradient between the conditioned room and the outdoors. In this scenario, heat added to the room via infiltration air is not nearly as substantial, but it still needs to be accounted for.

Duct heat transfer

In both single and dual hose systems, the duct removing the warmed air from the portable AC unit also generates heat. It is transferring hot air, after all. This heat is radiated back into the room. This further contributes to the inefficiency of the portable ac unit.

In a dual hose system, the secondary hose pulling outdoor air into the system to cool the condenser also gets hot and radiates heat into the room.

Old testing becomes new testing

Recall that the old standard for testing single hose portable AC units involved

  • the indoor chamber to be set to an ambient air temp of 80° F
  • the outdoor chamber to be set to an ambient air temp of 95° F for dual hose units. No outdoor air temperature was specified for single hose units

Now that you’re more familiar with the inefficiencies of portable AC units, consider how these conditions impacted the measured cooling capacity of tested units.

Infiltration air heat transfer is a major inefficiency of a portable AC system. Its effect is much more pronounced when outdoor air temperature is higher . Under old standards and guidelines single hose portable AC units could be tested at any outdoor temperature. It stands to reason that manufacturers would choose to conduct this testing at lower outdoor temperatures to boost the measured cooling capacity of tested units.

Heat added by ducting is also a major inefficiency. Old guidelines didn’t account for this inefficiency.

New testing

The US Department of Energy recognized the shortcomings of these old methods for testing portable AC units and instituted new rules and guidelines to provide a more accurate representation of portable AC cooling capacity.

The new standard for cooling capacity is called seasonally adjusted cooling capacity – SACC. This new standard is described by the equation

SACC = ACC95 × 0.2 + ACC83 × 0.8

Where, for single hose units

ACC95 = CapacitySD − Qduct_SD − Qinfiltration_95
ACC83 = CapacitySD − Qduct_SD − Qinfiltration_83

And for dual hose units

ACC95 = Capacity95 − Qduct_95 − Qinfiltration_95
ACC83 = Capacity83 − Qduct_83 − Qinfiltration_83

Note that the equations for single and dual hose units are very similar. The capacity and duct heat variables are slightly different to account for slightly different testing conditions required to test a system with two ducts instead of one.

Also note how SACC involves outdoor air temperatures of 83° F and 95° F. Granted, the higher temperature of 95° F only carries a 20% weight in the rating but it’s still present and it will still very much adversely affect the rating of any unit that does poorly at this temperature.

Furthermore, 80% of the rating requires testing at an outdoor temperature of 83° F. Previously, there was no outdoor temperature requirement for testing single hose units which led to highly inflated BTU specifications.

The most important take away

Most importantly, note how the equations above fully take into account the major inefficiencies of single hose units:

  • Heat added by infiltration air
  • Heat added by ducting

The dual hose equations also take these into account for dual hose units.

This means that you can compare the SACC of a single hose unit to that of a dual hose unit and the SACC alone will tell you which unit has a greater cooling capacity – which unit will be able to cool a room faster and to a lower temperature.

In the past, you would compare a 14,000 BTU single hose unit to a 14,000 BTU dual hose unit and you would be inclined to opt for the dual hose unit solely because it’s a dual hose unit. Dual hose units were supposed to be the more efficient option because they mitigate the effects of infiltration air with the addition of a second hose to the system.

Today, you simply have to compare the SACC. No more guessing is required.

For a single hose unit SACC will involve

ACC95 = CapacitySD − Qduct_SD − Qinfiltration_95
ACC83 = CapacitySD − Qduct_SD − Qinfiltration_83

And for a dual hose unit SACC will involve

ACC95 = Capacity95 − Qduct_95 − Qinfiltration_95
ACC83 = Capacity83 − Qduct_83 − Qinfiltration_83

Whichever unit has the higher SACC either has

  • a higher initial capacity – the first variable in the equation

or

  • less heat added due to ducting – the second variable

or

  • less heat added due to infiltration air

or some combination of the above.

The Whynter ARC-14S is a dual hose unit with a SACC of 8,900 BTUs.

The Honeywell HL14CESWB is a single hose unit with a SACC of 8,500 BTUs.

Both are 14,000 BTU units according to the old standard for measuring BTUs. Using SACC, we can clearly see how the Whynter has a better cooling capacity compared to the Honeywell.

We can say this NOT because the Whynter is a dual hose unit and the Honeywell is not, but because the Whynter has a higher SACC.

The LG LP1419IVSM is a single hose unit with a SACC of 10,000 BTUs.

The NewAir NAC14KWH02 is a single hose unit with a SACC of 9,500 BTUs.

Both of these units are also 14,000 BTU units by old standards of measurement.

Both of these units have a better cooling capacity than the Whynter ARC-14S.

Why? Certainly not because they are single hose units. This actually puts them at a theoretical disadvantage when it comes to infiltration air. They either have a much higher initial capacity and/or add less heat via ducting to account for their higher SACC value.

It is because of this higher SACC value that we can confidently say that they will cool a room faster and to a lower temperature than the dual hose Whynter ARC-14S.

Our own testing confirms this to be true.

We tested all four of these units – the LG, NewAir, Whynter, and Honeywell.

And the higher the SACC for the particular model, the faster it would cool our 150 sq. ft. test room and the lower the temperature it would be able to achieve in that test room given 2 hours of run time.

Conclusion

It’s certainly interesting to compare the inefficiencies of single hose vs dual hose portable air conditioners.

However, it’s by no means a requirement that you fully understand them when shopping for a portable air conditioner.

Simply compare SACC values to find the best performing units on the market. What you’ll find is that single hose models tend to have the highest SACC values - not because they’re single hose units but because they’ve been made in a way that maximizes their performance (and therefore minimizes their inefficiencies).

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