Engineering Stack Exchange
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Questions tagged [energy-efficiency]

110 questions
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Would it make sense to have a 12V lighting circuit in a house?

Modern LED bulbs must convert the standard household supply (for example $240\text{V AC}$ in the UK) into a DC supply at a lower voltage (usually $12\text{V DC}$ I think) for the LED array. This is done on a per-bulb basis. Does this waste much…
jhabbott
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How to design a house to be cooled passively?

I live in Louisiana these days, in an area that is known for its numerous antebellum plantation homes (circa early 1800s). While touring one of these homes it was clear that almost everything about the house was designed around keeping cool in the…
Chris Mueller
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Difference in energy consumption between empty fridge and fridge filled with bottles of water

I have about 12 bottles of water. If I want to minimize the energy consumption of my refrigerator, should I put these bottles in the fridge or leave them out?
fronthem
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What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?

It is known that Bluetooth Low Energy transmits data only during short time intervals called Connection Events. Connection events occur regullary with predefined period. The rest of the time Bluetooth LE device is does not transmit nor receive data.…
user1558573
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Is there a more active passive technique for removing humidity from the air besides salt blocks?

We can get really humid days sometimes. Recently I was digging around in boxes and found some old mineral specimens, and I set out a few of the salt crystal rocks. I soon found that they had pools of water accumulating underneath them, which…
New Alexandria
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Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

When waiting for the underground, I've always been wondering why we could not absorb the kinetic energy of the train to slow it down at the station and then to release this energy to help it accelerating during the starting up. This would also…
Noil
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Where to insulate Underfloor air distribution system in a temperate climate

I have a proposed underfloor air distribution system (UFAD) for a one level office in a temperate climate. Typically the demand for heating and cooling in this climate is about even for offices. However the building is well insulated and has a fair…
pandita
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Three-phase versus single-phase operation of a generator

My generator (a Fermont MEP-803A, 4 cyl diesel, 10kW rated) can run in three distinct modes: Single-phase 120V, in which one terminal is hot, and another is neutral Single-phase 120V/240V, in which two terminals are hot, and another is neutral. The…
Diogenes Creosote
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How Much Efficiency is Lost in a Gear Train

I want to get a rough estimate for the transmission efficiency of two different gear trains. One is a one-stage gear train with 11.67:1 ratio (140/12 teeth) and the other is a compound two-stage gear train with overall gear ratio of 18:1 (72/12 +…
Inf_E
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Third Rail vs Overhead Cable: which is more efficient in terms of electricity consumption?

I'm well aware that there are many different factors to be considered, such as ease of installation/maintenance, conversion from AC to DC, environment, distance, speed, frequency of turns, and so forth. Setting all of those aside for now, suppose we…
Ricky
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Calculation of the specific CO2 emission of a cogeneration plant for the produced electricity

Suppose I have a cogeneration plant that runs on natural gas and produces heat and electricity. The heat effeicieny is $\eta_{th} = 0.4$ and the electricity efficiency is $\eta_{el} = 0.4$. The burning of natural gas produces 215 g/kWh of CO2. For…
Emma
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Is the fill factor of a photo-voltaic cell constant?

An important factor in specifying the efficiency of photo-voltaic (PV) cells is called the fill factor (FF). It is defined as the ratio of the maximum power of the cell to the product of the open-circuit voltage $V_{oc}$ to the short-circuit current…
Moody
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What's more energy efficient: fewer air conditioners working at max capacity or more working at part capacity?

The central heat and air in the house I'm renting is unable to keep the house below 80 °F during the hot summer here (100 °F days). We've had 3 HVAC techs out to look at it and they all say there's "nothing wrong with the system" and that it's…
Dennis
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More efficient to use LED lighting than to open blinds for light and thereby lose heat when very cold outside?

Currently here it is 9 degrees Farenheit. My home is heated by electric resistance heating (not a heat pump, just plain heating coils). Am I correct in believing that it's more energy efficient to keep our wooden blinds and curtains closed and…
Paul
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In a diesel engine, does more heat leave the engine through the tailpipe or the radiator?

Diesel exhaust is hot, and there's a lot of it. Diesel radiators also get pretty hot. In a typical diesel engine, which one is dissipating more heat? EDIT: In response to a request for specificity below, I am specifically interested in heat losses…
Diogenes Creosote
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