Questions tagged [energy-efficiency]

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Comparing accelerated vs constant motion; inspired by real life example. Is reducing mass the way to save energy in vehicle use?

Energy consumption in jerky vs steady motion. An average European car travels 30 km per day in urban areas mostly. This requires starting and stopping due to traffic lights and congestion and results ...
Piotr's user avatar
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2 votes
0 answers
22 views

Is the electrical grid a centralized, decentralized, or distributed network? Which type is most efficient?

Is the electrical grid a centralized, decentralized, or distributed network? Each dot represents a generating station, consumer, or relay of electricity: Which type is the most efficient (has the ...
Geremia's user avatar
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27 views

Modeling an HVAC system's energy

I'm trying to model the energy consumption on an HVAC system with intermittent stops. As my model main parameters I use the following : A temperature and RH sensor of ambient air The HVAC working ...
Tomer Gigi's user avatar
0 votes
1 answer
40 views

Why is the fan efficiency zero at high flow rate?

How is the fan efficiency zero at the highest flowrate point (at which there is zero pressure rise)? I know the fan efficiency is given as $fan\_efficiency = output\_power/input\_power$ where ...
GRANZER's user avatar
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1 answer
22 views

How do i choose the most optimal turbine (Style, pitch, size...) for a very small scale Hydropower project?

I have a project in which I am designing a lightweight, portable hydropower system, and I'm unsure of how exactly I am to choose the correct style of turbine. For context, the turbine is only really ...
Eoi McTaggart's user avatar
0 votes
2 answers
63 views

How to calculate the optimum heat absorption rate of an object?

Consider I want to heat 1L water in a 1L aluminum container. That container I put on my stove that I heat with gas. I want to know, what is the optimum energy I can deliver to cook that water ...
AirCraft Lover's user avatar
8 votes
6 answers
5k views

Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?

I am curious about a method to enhance the efficiency of passenger aircraft during cruise speeds by integrating treadmill-like structures on the fuselage and beneath the wings without changing the ...
Siames's user avatar
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1 vote
0 answers
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Energy comparison of gas and electric automobiles

I'm trying to work out some comparisons of gas and electric automobiles, and am running into something that doesn't seem right to me. Let me explain: Let's say a typical electric car has a range of ...
Dave Tweed's user avatar
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1 vote
1 answer
135 views

What is the efficiency of Solar energy run turbines? Are they better or worse than Solar PV cells?

The Solar PV cell has an efficiency of 25-40%. Now steam turbines run by coal or some other fuel have an efficiency of approximately 60-80% What is the efficiency of steam turbines run by Solar energy?...
Hari Kumar's user avatar
0 votes
0 answers
49 views

Gear systems' efficiency comparison

For a given system, that requires a shaft-gear(n)-shaft connection, which system's configuration would be the most efficient to use (in terms of total energy loss minimization). Where gear(n) is n ...
user22128291's user avatar
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1 answer
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What would be the efficiency of dielectric elastomers if these were made with copper wire instead?

My apologies if this isn't the right Stack to ask about dielectric elastomers, but I couldn't find any other search result on other stacks about dielectric elastomers, except here. So, no matter how ...
Fulano's user avatar
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1 vote
2 answers
206 views

Do wind turbines placed on the sides of roads, powered by vehicles traversing the roads (traffic turbines) actually work?

Recently, ActionLab has posted this video https://www.youtube.com/watch?v=W8Oc3Etev34&t=1s, titled "Do Traffic Turbines Actually Work". It has caused a heated debate, as people discussed ...
Jelly Qwerty's user avatar
1 vote
1 answer
31 views

What is the impact of energy control in an AC in terms of cooling and power consumption?

Nowadays many inverter ACs come with energy saver modes claiming to run at 80% 60% etc… In this case wouldnt the cooling capacity also decrease? For eg if the AC is running at 60%, the AC compressor ...
Vipin Menon's user avatar
3 votes
2 answers
1k views

Why modern diesel engines have low compression ratio?

Modern diesel engines have low compression ratio (some only 14:1, old diesel has 23:1), if compression ratio is directly connected to thermal efficency, how this engines achieve good efficency? Can ...
user707264's user avatar
2 votes
3 answers
147 views

If it is more fuel efficient to mechanically inject gasoline into a high compression cylinder, why is it not done?

By the thermodynamics of the internal combustion engine (Carnot cycle), the higher the compression ratio, the more mechanical work is derived from the gasoline burned. So why is it not common practice ...
seanhalle's user avatar
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U-value for suspended ground floor

I'm about to finish U-value calculation for a house (an assignment for the Sustainable Technology for Buildings module) but I can't understand the formula. I've got all the data except from "ln&...
Przemek's user avatar
2 votes
1 answer
312 views

How efficient would a monotube steam generator without a pump in generating steam pressure?

So, the objective is to generate a water flow similar to a household water system (60 PSI) inside copper pipes that have 30 coil turns that are inside a stove that burns wood. A monotube steam ...
Fulano's user avatar
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0 votes
0 answers
34 views

How can I transport sunlight (with UV, IR etc...) across space?

I currently have a tiny vertical farm which I am trying to make as energy efficient as possible. A big chunk of my power consumption comes from LED lights which are powered by solar panels/batteries, ...
AndreAwb's user avatar
1 vote
3 answers
175 views

why can't you hybridise an internal combustion engine with a steam turbine

According to the internet, an internal combustion engine is powered by the pressure differential when the fuel expands into gas and has a maximum thermal efficiency of 50%. And a steam turbine is ...
Lorry Laurence mcLarry's user avatar
0 votes
0 answers
233 views

Are internal combustion engine more efficient than steam turbines

From what i understand the indicated thermal efficiency of an ic engine is measured at the fly wheel and is the measure of the amount of thermal energy being converted to mechanical energy please ...
Doctor Pinocchio's user avatar
1 vote
1 answer
82 views

Why is there not a large power or performance difference between these two air conditioners?

My parents have these two window air conditioners that are the same brand and look the exact same on the outside. The control interface is the exact same as well. I'm not sure how old they are but I'm ...
MICROexchange6's user avatar
1 vote
1 answer
36 views

Energy potential of a given quantity of carbon-based fuel directly vs through the grid

I'm a software engineer, but have taken some physics courses and almost went into mechanical engineering, but that was 30 years ago. I am beginning a deep dive into the efficiency of the grid ...
Oliver Williams's user avatar
1 vote
1 answer
67 views

Which are the Betz's limits for marine devices such as wave energy converters?

Nowadays, climate change is a relevant topic to reflect on the uses of renewable energies, such as the Sun, wind, oceans, tides, etc. Engineers are trying to design devices to extract the most power ...
Luke Solo's user avatar
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6 votes
5 answers
3k views

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 ...
Noil's user avatar
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0 votes
0 answers
22 views

What is the lowest energy solution for emptying a drip irrigation water collector : a mono-stable solenoid valve or a bistable coupled to a pump?

I have a water collector I want to empty everyday for drip irrigation. It is controlled by a micro-controller. I have identified three solutions: Use a bi-stable electro-valve and a pump: advantage ...
lalebarde's user avatar
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0 votes
0 answers
52 views

Understanding small DC motor curves (torque, efficiency etc)

I have a small DC motor/gearbox unit and the spec sheets is shown below. All* the units are measured at the gear box output, so 100 RPM would be 3,000 at the motor. I'm using it as a generator so am ...
KevInSol's user avatar
  • 117
0 votes
4 answers
137 views

Is it better to charge my electric car on windy days?

There are various dashboards (for example, here) that show the current energy generation mix and the overall CO2 emissions (gCO2/kWh). In the UK renewables can make up a large proportion of the total, ...
Gransden's user avatar
0 votes
1 answer
243 views

Heating pump/refrigerator - calculate efficiency

I'm wondering how I can calculate the overall thermal efficiency of my heating/refrigerator pump. Actually I have this AC/heating pump unit from Samsung (P/N: AR09TXFYBWKNEE). I've placed a power ...
MadSch's user avatar
  • 101
1 vote
0 answers
64 views

How to calculate the actual COP of a compression for a given outdoor temperature?

Given a chiller having a nominal COP value, how can we compute the actual COP for a given outdoor temperature. In this regard, is there any difference between compression chillers and absorption ...
Dana's user avatar
  • 11
2 votes
4 answers
2k views

How turbo engines increase efficiency if have lower compression ratio than naturally aspirated engines?

I know that efficiency depends on compression ratio(CR), NA engines always has higher CR than turbos,so how turbo engine can have better efficiency?
user707264's user avatar
-1 votes
1 answer
53 views

Minimizing home heating costs [closed]

I live in an old rental house with 12 foot ceilings and zero ceiling fans. I am trying to conserve as much energy as possible as heating costs are expensive. I have placed plastic on all of my windows ...
Kasi Darnell-Tibbs's user avatar
0 votes
1 answer
102 views

Understanding "total primary energy supply"

I am trying to wrap my head around the diagram and explanation here but can not understand completely how it is computed. https://energyeducation.ca/encyclopedia/Total_primary_energy_supply For ...
Artium's user avatar
  • 101
2 votes
1 answer
461 views

Converting between MMBTU and MWh

a quick question: I want to convert between MMBTU and MWh to get at emission factors from energy. I have the following information: I use the data given in 40 CFR 98 (see EPA source here) by the EPA ...
Moritz Schwarz's user avatar
2 votes
1 answer
1k views

Dehumidification calculations

I'm looking at options for DIY dehumidification and am hoping to get a sanity check on some calculations, and verification that I'm using the right factors in the right way. As a reference point, I ...
fixer1234's user avatar
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1 vote
0 answers
70 views

How are NASA's mars rovers able to operate with such little energy?

The latest Mars rover being, NASA's Perseverance, uses the Multi-mission radioisotope thermoelectric generator, which has a maximum power output at the beginning of it's operational life of 125 watts, ...
C-Consciousness's user avatar
1 vote
1 answer
70 views

What is the efficiency of direct electric heating versus water heated via electricity?

I am attempting to keep plants warm in a greenhouse. Therefore, I assume that heating the soil should be most efficient, as that's what plants seem to care about the most (i.e. the temperature of the ...
Nick Bolton's user avatar
1 vote
0 answers
49 views

Equations of motion in matrix form and energy consumption

I am working on Lagrangian derived high-dimensional motion equations for a robot in matrix form. The structure of such an equation is known: $M(q)\ddot{q}+C(q,\dot{q})\dot{q}+G(q)=0$ In here, $M(q)$, $...
dtn's user avatar
  • 226
3 votes
2 answers
72 views

What are some technical problems with generating electricity using a gas turbine or combustible engine at a gas flaring site?

Numerous oil and gas exploration sites practice flaring for safety and disposal of unwanted low calorific gases. However, instead of just standalone burning the gas, why can't a gas turbine or ...
ARJ's user avatar
  • 105
0 votes
1 answer
416 views

Are AC generators more efficient than DC generators?

I've been doing some research into AC and DC generators, and I was wondering if AC has any advantages in terms of efficiency. Given that AC generators are usually brushless while DC generators ...
Jack's user avatar
  • 11
0 votes
2 answers
113 views

What would be a reasonable estimate for the amount of petroleum needed to find, produce and deliver one barrel of petroleum?

A basic "balance sheet" might allocate fuel needed for exploration, well development, production, crude oil transportation, refining, further product transportation and delivery to a ...
user217348's user avatar
0 votes
2 answers
375 views

Why is Carnot Factor defined as 1 - (T(cold) / T(hot))

This is the proof I've found for the Carnot Factor: $$S = \frac{Q}{T} \qquad \qquad (1)$$ $$S_{in} = S_{out}\qquad \qquad (2)$$ Because entropy stays the same when ...
DarkTrick's user avatar
  • 125
0 votes
1 answer
164 views

How does the efficiency curve of a well pump shift with speed?

Well pump manufacturers publish "efficiency curves" for well pumps, such as this one (the curve that is most sharply convex down, whose Y axis is read from the "% EFF" scale on the ...
Diogenes Creosote's user avatar
4 votes
2 answers
407 views

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 ...
Paul's user avatar
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0 votes
1 answer
126 views

Which power plant will generate more electricity in the below discussed scenario?

There are two identical power plants(i.e same turbine dimension and same generator configuration). Both have a hot reservoir. Coal is burnt on both power plant to make the temperature of the hot ...
Tank's user avatar
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1 vote
0 answers
335 views

Optimizing flue gas temp for maple syrup evaporator

I have a simple maple syrup evaporator. Fuel is burned in a firebox located under 1mm stainless steel pans containing maple sap--which becomes syrup once enough water is evaporated. After passing ...
Asa's user avatar
  • 11
0 votes
1 answer
61 views

explaining ohmic loss and understanding inverter efficiency curve

I'm trying to understand an efficiency curve from PVsyst, using this documentation However, I'm not sure what this sentence means: This production is penalized by an ohmic loss$^1$ of the internal ...
Lime's user avatar
  • 105
0 votes
1 answer
40 views

Where can I find efficiency metrics for diesel engines?

I am doing long term planning for a small fleet of tugboats. A lot of the engines (propulsion, generators, hydraulics) are Detroit Diesels of various sizes (e.g., 4-71, 6-71, 12V-71). Newer engines ...
Gene McCulley's user avatar
3 votes
2 answers
195 views

Natural ways for passively cooling/heating a home?

I always think about how there surely must be natural ways to cool/heat a house, rather than using electricity, like solar panels, heaters, and AC. Does anyone have any good examples of houses/...
OtheJared's user avatar
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3 votes
0 answers
40 views

Optimization: Most efficient way for multiple people to move boxes

We are moving house in a few weeks and have a couple of people helping moving the boxes. My previous experience from moving is of queues building up in small hallways and people getting tired from ...
user avatar
3 votes
0 answers
195 views

PMDC Motor Characteristic Graph

I am trying create a graph similar to as shown below. However, I am confused as to how the torque is related to the characteristics. The graph that is to be replicated for certain parameters: The ...
Benny's user avatar
  • 31