Just found some reviews of robotic vacs (french gadget reviewer: http://www.lesnumeriques.com
) and want to compare them together. ...Power-consumption comparative spec:
27W /4W (charging/stand-by)
€6/year more expensive in use than Dyson DC29 canister (regular use - twice a week) ...
** - Dyson DC29 Allergy Canister
; power: 1360W (declared: 1400W; efficiency comparable to regular 2000Watt vac) €5/year (when used twice a week for 20 minutes; other >2000W vacs - €6.5/year), 80 (tested)/82dB (declared)
Peter, I wish to numerically challenge three errors that I see in the Roomba / Dyson data that was published by lesnumeriques. While I must now postpone any further comments about Roomba's "4W" trickle charging power, I would like to attempt correction of these errors that lesnumeriques is propagating. They are:
A) "27W" as the input power to a 780 Roomba (or any other Roomba that uses a 22.0V/22.5V, 1.25A PSU) during the high-rate portion of battery charging.
B) "€6/year more expensive in use than Dyson DC29 canister (regular use - twice a week)" is backwards. The Dyson DC29 will cost about the same to operate as a 780 Roomba while Roomba spends 6X more time working. IOW, lesnumeriques' claim that a 780 will cost €(5 + 6)/year = €11/year, can't be true.
C) "€5/year (when used twice a week for 20 minutes...)" as the cost of operating the Dyson DC29 canister is less than what Peter would pay for the energy total that I compute. Either lesnumeriques' energy estimate is less than mine, or energy rates are not universal across Europe. If all computations have been correctly done, the fault here is lack of universal expression of energy consumption. A better tactic for expressing the differences is by ratios of energy consumptions, and omission of currency.
I will discuss the above list elements in the same order:
========= "A) '27W' as the input power to a 780 Roomba during .......========
========= the high-rate portion of battery charging."...................========
"27W", as lesnumeriques indicates is wrong because it does not match the input power listed by iRobot on the PSU's label. Also, 27W is roughly equivalent to the PSU's output power, viz., P = E,(V) * I,(A) = 22.5V * 1.25A = 28 watts; and, we know the PSU's input power must be greater than its output power because the conversion from input to output is not lossless.
========= "B) '€6/year more expensive in use than Dyson ..........==========
========= DC29 canister(regular use - twice a week)' " .............==========
Discussion of this statement is muddied by the "(regular use - twice a week)" wording. Are we to assume twice a week, 20-mins Dyson cleaning and twice a week 780 cleaning until battery depletes; or, is it 20-mins twice a week for each machine?
I will proceed without an answer to that question, and simply presume Roomba operates for 2-hours each session, or 4h per week. To estimate the energy cost of operating the 780 for each cleaning event, I will draw on a post that was prepared for gangel, in which two tables organized time periods that various power consumptions occurred to prepare Roomba for a cleaning mission. See the "Appendix", ending this post, to review allocated time periods and reasonable power dissipations (factors which have been adjusted for use in this post).
From the calculations in the appendix the energy expense of operating a 780 Roomba for 52 weeks is: 43 kWh.
From element (C), below, the energy cost of operating the DC29 canister twice each week over 52 weeks is: 47+ kWh.
Roomba spends 6X more time working, but uses less energy than the prescribed Dyson operation!
======= "C) '€5/year (when used twice a week for 20 minutes...)' " .........========
Relative to the DC29 Canister, I don't know what "declared: 1400W" means, so I will use the Dyson stated power consumption of "1360W" in the annual energy usage calculation for 52 * 2 * 20-minute sessions each year. This results in a total energy accumulation of: e,(Wh) = (52instances/year) * (2/3)hour/instance * 1360 watts = 47147 watt•hours/year, or 47+ kWh/y.
If Peter were to pay for this energy, his annual bill would be:
(€0.1329/Wh) * 47.147Wh/y = €6.27
to operate the DC29 in the manner described. Note that my calculated expense is €1.27 larger than the lesnumeriques' value (of "€5"); and, that could be due to differences in district (Peter's vs. lesnumeriques') rates, or due to miscalculation of the required energy by lesnumeriques (it does not display any calculations, only results), or a combination of both.
================================ IN SUMMARY =============================
List element (A) has been shown untrue.
List element (B) has been shown untrue.
List element (C) has been shown to be questionable.
I again suggest that nothing reported by lesnumeriques is worth spending
================================= APPENDIX ==============================