Electrical and Gas Powered Water Boilers

The other day I got two water boilers as birthday presents. The Braun Multiquick 3 is an electrical powered water kettle for kitchen use and the Primus ETA Lite is a backpacking stove running on canister gas. The manufacturers state their water boilers abilities to boil water “fast”: 200 mL in 45 sec and 0,5 L in 2 min 45 sec respectively. Additionally, Primus states their ETA technology to achieve efficiencies close to 80%.

Now, which one is the fastest, and what are their efficiencies?

To find out I ran a series of tests[i] measuring the time to boil various volumes of tap water. Then I calculated the energy spent by the water boilers based on effect data submitted by the manufacturers, and the energy absorbed by the water based on the water volumes and the temperature gain.

Braun Multuquick 3

Volume	Time to Boil	Energy Spent	Energy Absorbed	Efficiency
(mL)	(s)	(J)	(J)	(%)
200	51	112200	71400	64
500	98	215600	178500	83
1000	197	433400	357000	82
1700	337	741400	606900	82

The time to boil 200 ml water by the electrical powered water kettle from Braun was measured to be 6 seconds  (13%) slower than stated and the mean efficiency was calculated to be 78%.

Primus ETA Lite

Volume	Time to Boil	Energy Spent	Energy Absorbed	Efficiency
(L)	(s)	(J)	(J)	(%)
100	34	51000	35700	70
200	64	96000	71400	74
300	97	145500	107100	74
400	134	201000	142800	71
500	171	256500	178500	70

The time to boil 500 ml water by the gas powered backpacking stove from Primus was measured to be 6 seconds  (3.6%) slower than stated and the mean efficiency was calculated to be 72% which is ballyard “close to 80%” as stated by Primus.

Comparing the two beasts at the two common data points, 200 mL and 500 mL, the electrical device proved to be faster than the gas device by 13 seconds and 73 seconds respectively. Similarly, the electrical device was the more efficient overall.

To sum up, the water boilers appear to live up to manufacturer claims and they are both very energy efficient.

Calculations

The energy spent was calculated from the stated effects multiplied by the time to boil:
Energy (Joule) = Effect (Watt) x Time (s)

The energy absorbed was calculated from the water volume converted to weight multiplied by the rise in temperature multiplied by calories converted to Joule:
Energy (Joule) = Volume (ml) x 1 g/ml x 85 (K) x 4.2 Joule/calorie.
The rise in water temperature was calculated from the boiling point of water minus the tap water temperature: 373K - 288K = 85K.

Technical Data:

	Braun Multuquick 3	Primus ETA Lite
Maximum capacity	1,7 L	0,5 L
Effect	2200 W	1500 W

Additional Data (stated for reference):

Room temperature: 295K (22 °C)

Tap water temperature: 278K (15 °C)

Atmospheric pressure[ii]: 1020.4 hPa

Humidity[ii]: 80%

Elevation: 50 m

Gas: 20% Isobutane, 80% Propane mixture from MSR.

Endnotes

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[i] In order to cool down the water boilers between each boil they were filled with cold tap water three times and left to stand at least one minute each time.

[ii] Source: Danish Meteorological Institute

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2014-11-10

Additional test

I visited my brother, Kåre the other day celebrating the birthday of his oldest son, Rasmus. Kåre has a MSR Reactor 1.0 L, a reversible vacuum cleaner and an anemometer. So we did a few boils while his guests were entertained otherwise:

The Reactor boiled 0.5 L of 12 C cold water in a bit less than 2 minutes at zero wind. Using a stated of 2750 Watt we calculated its efficiency to be 56%. Bear in mind the uncertainty of a one-point measurement and a stated value found on the Internet. However it is a bit low when compared to the 72% of the Primus ETA Lite. On wind stability: We found the Reactor stable up to at least 17 m/s when the anemometer maxed out. In comparison the Primus ETA Lite blew out at that wind speed, while it was ok at 5-6 m/s. These initial results call for a more thorough study. Will return.

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