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Heat Chamber Test Results: DC Powered Rooftop A/C Units

Heat Chamber Test Results: DC Powered Rooftop A/C Units

Have you ever wondered why some DC powered air conditioners cost so much more than others? Have you ever purchased an A/C based on the specs only to be disappointed in the actual performance of the unit?

We have too, so we put many of them to the test, including the Nomadic X3, Dometic RTX 2000, Velit 2000R, Turbo Air 2, and the Indel B Plein Aircon.

ANALYZING DRIVING FACTORS FOR THIS PRODUCT COMPARISON

The decision to invest in a DC powered air conditioner over an AC powered counterpart hinges on a delicate balance between efficiency gains, cooling performance, and upfront costs.

In the following sections, we explore key metrics such as energy consumption, cooling capacity, and upfront costs to provide valuable insights into the performance differences between the leading units on the market today.

KEY EFFICIENCY METRICS

  • Energy Consumption
  • Cooling Performance

Performance of off-grid rooftop air conditioners is evaluated based on several key metrics, which include energy consumption and cooling capacity. For a specified cooling capacity, lower energy consumption indicates higher efficiency, while higher cooling capacity ensures adequate cooling performance, particularly in hot climates.

Units with a high cooling capacity will naturally require more energy. What makes a unit efficient is the ratio of energy output compared to the energy input, also known as the coefficient of performance, or COP. Two units can be capable of the same cooling capacity, 7,000 BTU/hr for instance. Measured in watts, this is approximately 2,050 watts (3,412 BTU is equivalent to 1000W).

The energy required to produce 2,050 watts of cooling power will largely depend on the ambient conditions and how well the cooling system is designed. This is where large, established companies with big research and development budgets, advanced (and sometimes proprietary) technology, and years of experience in cooling system design excel ahead of the new and smaller companies on the market.

A well designed cooling system should see a COP of 2.2-2.4, meaning to produce 2,050 watts of cooling, only 854-932 watts of power is required. The size of the condenser, size of the evaporator, refrigerant type, refrigerant charge level, compressor capacity, air flow, and type of fan all play a role in achieving a high COP. A delicate balance in the design of these components is crucial to performance as well as efficiency. 

TEST RESULTS

The tests which produced the results in the below infographics were performed by an independent test lab. All test procedures and conditions were controlled to maintain equal environments and an apples-to-apples comparison to monitor temperature pull-down and runtime.

The air conditioning units were installed in their factory default state and set to Auto mode with a set point of 75F.

The internal chamber was sized to approximate the interior volume of an extended wheelbase van.

A nominal and equivalent heat load was placed inside the chamber for each test to simulate real world conditions.

Interior ambient air temperature sensors recorded how effectively the air conditioning units distributed and cooled the air.

Each test was timed to document the runtime until the 200Ah battery source was exhausted or until the low voltage cut-off was reached.

The basis of the test was not to measure cooling capacity of the unit to compare to the claimed rating. Rather, it was meant to provide you with a controlled, real-life example of what to expect from a roof-mounted A/C when installed on an adventure van. 

We can see in the above graphic that all units were able to bring the interior air temperature down, some faster than others. The speed at which the interior air temperature drops is an indicator of the cooling capacity as well as the air volume the A/C is able to circulate. The colder the evaporator and the more air volume a unit can pass through the cold evaporator, the faster the temperature will decrease.

Most of the units were able to bring the air temperature close to the 75F set point. It's obvious that two units were not able to achieve the 75F set point; the Nomadic X3 and the Indel B Plain Aircon.

There are two possibilities for this; the units did not have the required cooling capacity to bring the temperature down any further, or the position of the ambient air temperature sensor on the unit is in a location where it is drawing in and recirculating the cold air it is producing.

In the case of the Indel B, it is only a 4,100 BTU/hr capacity so it is likely underpowered for this application.

The Nomadic X3, however, advertises an 11,830 BTU/hr cooling capacity. That rating is either largely inflated and based on the potential capacity of the compressor and components and/or it is a poorly designed cooling system and the components are not working in unison. In either case, the performance of the unit is going to be disappointing for the user. 

 

The actual temperature inside a space undoubtedly impacts comfort. Equally important, though, is the significance of relative humidity. This cannot be overstated. In environments such as RVs or camper vans, where occupants spend prolonged periods, maintaining an optimal balance between temperature and humidity is paramount for well-being. High humidity levels can exacerbate discomfort, leading to a clammy feeling, increased perspiration, and a heightened perception of heat, even at lower temperatures.

You'll notice all units initially increase humidity in the air. This is due to the cooling of the air inside a sealed chamber. The air gets cooler while the moisture content remains relatively the same. That is, until the evaporator reaches a cold enough temperature for the moisture in the air to condense and freeze onto the evaporator. We can see this takes some time for each unit to achieve but there is a steep drop in humidity with higher performance units, like the Velit unit. 

The Nomadic X3 on the other hand continues to climb, indicating it is either insufficient in cooling the air enough for it to condense on the evaporator and/or the evaporator is not cold enough to freeze the moisture and thus remove it from the air. 

You'll notice above, the Dometic RTX 2000 excels in Interior Ambient Temperature Vs Runtime. However, the humidity level with the Dometic RTX 2000 was the highest of all units, although it was able to begin removing humidity after approximately 160 minutes.

The Velit 2000R proves to be the most balanced unit between ambient temperature, runtime, and relative humidity. 

For reference, a chamber at 85F (like with the X3) and 29% humidity is going to be far less comfortable than a chamber at 77F and 25% humidity. An environment at 85F and 29% humidity has more water vapor content in the air than a chamber at 75F and 40% humidity! (0.511 g/m^3 vs. 0.425 g/m^3).

Achieving an ideal balance of temperature and relative humidity fosters a comfortable and healthier indoor environment.

RUNTIME

In addition to higher overall performance, the Dometic RTX 2000 and the Velit 2000R showed a substantial increase in runtime over the other units, a testament to their efficiency.

As the runtime on 200Ah alone did not provide a full 8 hours of cooling (an established desirable minimum for sleeping), each unit was assessed to determine how much additional capacity would be required to produce a full 8 hour runtime.

With the temperature pull-down of the space already complete on the first 200Ah, each additional 200Ah of battery capacity will provide additional time beyond the initial 200Ah. In the chart below, the runtime on an additional 200Ah would also apply if the interior temperature of the van was already cooled, from the engine driven factory A/C for instance.

For the Velit and the Dometic RTX, only one additional 200Ah battery (400Ah total) would be required to reach the 8 hour benchmark. The remaining units require two additional batteries (600Ah total). This presents a significant cost difference in batteries alone. 

Leveling the playing field and providing each unit with 600Ah, the Indel B performs the worst with an 11 hour and 21 minute expected runtime.

The X3, not much better, can be expected to run for 11 hours and 42 minutes.

The RTX 2000, the top performer in this category, can be expected to run for 15 hours and 57 minutes.

The Velit can be expected to run for an impressive second place finish at 12 hours and 42 minutes.

Not to mention the RTX and the Velit will keep the space 8-10 degrees cooler, reduce the humidity, and reach your desired set point faster.

Scroll ——>

  Dometic RTX Velit 2000R Turbo Air II Indel B Plein Aircon 12V Nomadic X3
Retail (w/ Install Components, freight not included) $                            3,099.97   $                           1,599.00    $                           2,995.00 $                           4,484.00 
Advertised Cooling Capacity 6824 BTU/hr 8000 BTU/hr 22,000 BTU/hr 4,100 BTU/hr  11830 BTU/hr
1-hr Pull Down from 100F 78F 82F 81.3F 85.3F 85F
Runtime on 200ah 287 Minutes (4h47m) 256 Minutes (4h16m) 230 Minutes (3h50m) 221 Minutes (3h41m) 218 Minutes (3h38m)
Max Current @12V 51.9 64.2 57.4 55.8 89.6
Heat Pump No No No No No
Active Shutter ADB No Available No No No
Additional Runtime on 200ah 335 Minutes (5h35m) 253 Minutes (4h13m) 226 Minutes (3h46m) 230 Minutes (3h50m) 242 Minutes (4h2m)
Additional Cost of 200ah Battery $                            1,305.00   $                           1,305.00   $                           1,305.00   $                               1,305.00   $                           1,305.00 
Additional cost of Batteries to achieve 8hr runtime $                            1,305.00   $                           1,305.00   $                           2,610.00   $                               2,610.00   $                           2,610.00 
Total cost for 8hr runtime (in 200ah increments) $                            4,404.97   $                           2,904.00    $5,605.00 $                           7,094.00 
Total Runtime Capability on 600ah 15h57m 12h42m 11h22m 11h21m 11h42m
           
Running  on Max dB @ 28" 66dB 72dB 78dB 71dB 74dB

 

COST-BENEFIT ANALYSIS AND CONCLUSIONS

From the data shown in the table above, cost for 8hr runtime (in 200ah increments):

  • Nomadic: $7,094.00
  • Indel B:: $5,605.00
  • Dometic: $4,404.97
  • Velit: $2,904.00

A higher price point can sometimes give a perception of high quality and performance. There are many products on the market that live up to this notion. However, equally prevalent are products that don't. 

Considering the cost premium of the X3 compared to the other units like Velit, at retail, there is a staggering $2,885.00 difference in the upfront cost of the unit itself. In order to achieve an 8-hour runtime for both units, three 200Ah batteries are required for the X3 for a total of 600Ah, whereas only two 200Ah batteries would be needed for the Velit 2000R.

With an average cost of $1,305 for each additional 200Ah battery, this puts the actual cost difference between the Velit 2000R and the Nomadic X3 at a whopping $4,190.

And what does this additional cost net you with the Nomadic X3?

  1. Higher temperatures
  2. Higher humidity
  3. Shorter runtimes
  4. Slightly smaller footprint on the roof
  5. Clever marketing

Empirical data reveals that a high price point and a cool name does not equate to real-world performance.

Innovation happens in a lab, not in a studio. 

Next article ARCO Zeus vs Wakespeed Alternator Regulator: The True Cost Difference

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