Questions tagged [energy-efficiency]
The energy-efficiency tag has no usage guidance.
97
questions
2
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4answers
282 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?
-1
votes
1answer
48 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 ...
0
votes
1answer
42 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 ...
2
votes
1answer
60 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 ...
2
votes
1answer
97 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 ...
1
vote
0answers
51 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, ...
1
vote
1answer
53 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 ...
1
vote
0answers
29 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, $M(q)$, $...
3
votes
2answers
67 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 ...
0
votes
1answer
48 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 ...
0
votes
2answers
103 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 ...
0
votes
2answers
64 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 ...
0
votes
1answer
47 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 ...
4
votes
2answers
135 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 ...
0
votes
1answer
83 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 ...
1
vote
0answers
56 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 ...
0
votes
1answer
32 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 ...
0
votes
1answer
31 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 ...
0
votes
0answers
12 views
How to calculate the ideal and realistic estimate of thermal efficiency of absorption chiller?
How Can I calculate the ideal and a realistic estimate of the thermal efficiency of the system (thermal, electrical and water) per 1 kWh chilling energy (removed from the chilled water)?
What is the ...
3
votes
2answers
98 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/...
3
votes
0answers
34 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 ...
3
votes
0answers
72 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 ...
1
vote
3answers
67 views
Practicality of energy recovery from HVAC systems?
I've been thinking about ways to maximize efficiency in large buildings, and one thing I thought of was to place some sort of turbine in the exhuast vents or smokestacks of factories, power plants, ...
0
votes
0answers
24 views
at what point is increasing pressure ratio diminishing in returns?
piston engines of ww2 planes had pressure ratio of at least 10, while jet engines were still vastly superior with a pressure ratio of only 3.
Certainly pressure ratio of 1 would bring 0% fuel ...
-1
votes
1answer
97 views
How much time to melt marshmallow under heat lamp?
Using the Specific Heat Formula, I found that I need to apply 612J of heat to melt 18g of marshmallow. Marshmallow has a specific heat of 2 J/(g*C), melting point of 98.6°F, and a starting room ...
0
votes
0answers
92 views
Energy Wasted in Electromagnetic Motor Actuator Vs Human Muscle Actuation
I would like to know if the energy utilized by a robotic arm is greater compared to the energy utilized by human arm. Robotic arm is essentially servo motors that use electromagnetic field to create ...
-1
votes
1answer
33 views
Why Do Airborne Wind Energy Systems Use Kites And Not Balloons?
Title says it all,
Why are AWE-companies like Makani spending years and millions of dollars developing drones, rather than simply using a balloon-based design?
Wouldn't it be easier and faster to get ...
1
vote
3answers
137 views
Why are some submarines using liquid oxygen for combustion?
I think som submarines like Kockums use liquid oxygen instead of compressed air for driving their combustions engines. Is it more energy efficient to oxygen enrich the air before burning it compared ...
2
votes
0answers
22 views
One dimensional U-Factor Calculation - How to determine indoor / outdoor film resistances
Can someone clarify the ASHRAE Fundamental 2017 (SI Units) (See Below) Indoor and Outdoor film resistances. The manual states that it comes from Table 3 and in the description of table 3 it states &...
1
vote
1answer
97 views
Laser Power vs Efficiency
Is there some kind of graph or relation between laser power and efficiency. What I'm trying to find out is whether the efficiency of a laser decreases with increase in power or is it that there is no ...
4
votes
1answer
142 views
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 ...
-1
votes
2answers
28 views
Relation between engine size and its power to weight ratio
Is there a relation between engine size and its power to weight ratio? For example if you shrink the engine to half the size will it have exactly half the power?
6
votes
3answers
972 views
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 ...
1
vote
2answers
60 views
How much weight has weight in fuel efficiency?
Comparing the official fuel efficiency figures for several cars, I was surprised to discover that the Smart Fortwo has a weight between 750 to 800 kg and needs 4.3 L/100 km, but the VW Polo with a ...
3
votes
1answer
36 views
Question about flow temperature and storage temperature in a cogeneration plant
Let's assume I have a cogeneration plant that produces heat with a nominal output. The heat is given into a heat storage tank, which is filled from above. The maximum flow temperature of the ...
5
votes
1answer
151 views
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 ...
2
votes
0answers
24 views
Energy/Efficiency Calculations for Large Multi-stage Package HVAC
I frequently use the Equivalent Full Load Hour (EFLH) estimation method to calculate the expected energy usage for commercial HVAC equipment. While not ideal, it works well enough to given an order ...
6
votes
3answers
1k views
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 ...
0
votes
0answers
71 views
Most efficient turbine for harnessing energy from bidirectional air flow?
I am currently working on designing an oscillating water column as part of a project. In summary:
OWC are devices with a semi-submerged chamber or hollow open to the
sea below, keeping a trapped ...
2
votes
1answer
61 views
Effect of Pressure on Combustion efficiency (of hydrogen) in excess air
Can somebody explain relation between combustion efficiency and pressure in lean mixtures using any kind of chart or mathematical equations?
At first glance I thought, combustion efficiency increases ...
-2
votes
2answers
43 views
Does utilizing exhaust energy to supercharge ("turbocharging") increase the thermal efficiency of a gasoline internal combustion engine?
The work done by a turbocharger increases the inlet charge without much of a burden to the exhaust flow. This increases the amount of air (and fuel) that flows into the engine. How does this affect ...
4
votes
2answers
152 views
Do 3 blade wind turbines generate more power than a 9 blade, all else being equal?
After doing some research, I have come to the realization that 3 blade design horizontal turbines have the greatest maximum coefficient of performance. Most sources seem to agree a Cp of ~0.45 at TSR=...
1
vote
3answers
37 views
Efficiency of an engine
What is meant by thermodynamic efficiency of an engine?
and what are the factors that affect the thermodynamic efficiency of a diesel engine?
0
votes
2answers
134 views
Refute my assumption: Bearings Don't Improve Efficiency
If two surfaces rub together with a normal force between them, friction is generated. You could add lubrication between those two surfaces and reduce that friction.
Bearings essentially consist of ...
5
votes
3answers
1k views
Is it true that four-wheel drive is less efficient and if so, why?
I have heard many times that four-wheel drive is less efficient than two-wheel drive. Many car producers have a normal drive mode where only two wheels are powered, and turn the four-wheel drive on ...
0
votes
1answer
1k views
calculating the efficiency of a microwave oven
If I want to calculate the efficiency of a microwave oven, I have the input Energy (= power (watts) x time (s)) and the output which I measured using temperature difference (q=mct).
So do I divide ...
0
votes
2answers
39 views
Would some manufacturing processes be more efficient if driven differentially by a single motor, up to ~150 kW, than multiple lower-rated motors?
I'm writing a discussion paper on the potential energy efficiency benefits of integrating different manufacturing processes by co-location on the same site. One possible field for integration is in ...
3
votes
1answer
116 views
What is the difference between a diffuser and a duct in turbines?
I have been reading this paper, which addresses the advantages of diffusers in cross flow turbines.
The abstract says (emphasis is mine):
A CP’s extraordinary improving resulted when yaw increased ...
1
vote
1answer
72 views
Calculate Efficiency Loss of a Leak in a Hydraulic Cylinder
I am trying to figure out what the efficiency loss of a leaking hydraulic cylinder is. This master's thesis found that a controllable pitch propeller (essentially a hydraulic cylinder inside a ...
2
votes
1answer
74 views
Converting grams of fuel per kWh of energy
Is there a database showing how many grams of a particular fuel generates how many Kilowatt hours of electricity?
