Questions tagged [energy-efficiency]

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1 answer
59 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 ...
0 votes
1 answer
116 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 ...
0 votes
0 answers
20 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 ...
0 votes
1 answer
53 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 ...
0 votes
1 answer
37 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 ...
0 votes
0 answers
30 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 ...
0 votes
4 answers
97 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, ...
1 vote
0 answers
21 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 ...
2 votes
4 answers
415 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
1 answer
49 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
2 answers
107 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 ...
2 votes
1 answer
80 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
1 answer
192 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
0 answers
56 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
1 answer
58 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
0 answers
31 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
2 answers
69 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
1 answer
63 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
2 answers
95 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 ...
4 votes
2 answers
153 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 ...
1 vote
0 answers
130 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
1 answer
35 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
1 answer
33 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 ...
3 votes
2 answers
106 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
0 answers
36 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 ...
2 votes
1 answer
82 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?
3 votes
0 answers
111 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
3 answers
70 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
0 answers
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
1 answer
189 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
0 answers
104 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
1 answer
35 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
2 answers
65 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 ...
0 votes
2 answers
143 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 ...
1 vote
3 answers
181 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
0 answers
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
1 answer
157 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
1 answer
156 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
2 answers
29 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
3 answers
1k 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 ...
3 votes
1 answer
39 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
1 answer
227 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
0 answers
25 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
3 answers
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
1 answer
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 ...
3 votes
1 answer
131 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 ...
9 votes
1 answer
4k views

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 ...
0 votes
0 answers
81 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 ...
0 votes
2 answers
40 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 ...
-2 votes
2 answers
44 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 ...