Amps v Amp hours v Amps/Hr

[sailorchic34]

Originally Posted by transmitterdan

There is a mistake in this first sentence. You can talk about BTU and gallons in the same sentence but you can't talk about BTU and GPM because the units don't balance. You can talk about BTU/minute and gallons/minute because these units balance. A BTU is the thermal energy required to raise one pound of water one degree Fahrenheit. There is no time in that description, only volume (assuming 8.33 pounds per gallon).

You are correct. Its BTU per minute. A GPM time unit is not needed to calculate BTU per minute or to calculate BTUH. Done all the time from jsut a GPM number.

[StuM]

Originally Posted by sailorchic34

Sorry a minor booboo. Lets call it 50,000 MBTU, not MBH. So no we don't need a additional time measurement.

It doesn't matter whether it's heating systems or electrical systems. You still do not grasp the basic mathematical and physical concepts and the importance of being precise in your use of units.

So let's look at your two results.

You first said that someone would need 50,000 MBH per minute to meet there requirements.

That, as you admit, is incorrect.

But without seeing your working to tell where you went wrong, we can't tell what we need:

When she said 50,000 MBH per minute, which part do we ignore. The "per minute" or the "H"? Did our "engineer" mean that we need to generate 5,000,000 BTU per minute (MBTU/m) or 5,000,000 BTU per hour (MB/H). One takes 60 times as much power as the other.

So not a "minor booboo". It's the reason for this whole thread.

[sailorchic34]

Originally Posted by Lars_L

I want to start from the beginning and look how far we can agree.
Lets do the same way as when you eye is tested. How far down the list can you agree?

Some one-dimensional units:

Time:
Day (d)
Hour (h)
Minutes (m)
Seconds (s)

Length:
Meter (m)
Decimeter (dm)
Centimeter (cm)
Foot (ft)
Inch (in)

Volume:
Cubic meter (m³)
Cubic decimetre (dm³) even called litre (l)
Cubic centimetre (cm³)
Gallons (g)
Cubic foot (ft³)
Cubic inch (in³)

Two-dimensional unit:

Flow = Volume per Time

Cubic meter per hour (m³/h)
Litre per hour (l/h)
Litre per minutes (l/m)
Litre per seconds (l/s)
Gallons per hour (g/h) or (gph)
Cubic inch per minutes (in³/m)

Agree 100%

[sailorchic34]

Originally Posted by StuM

It doesn't matter whether it's heating systems or electrical systems. You still do not grasp the basic mathematical and physical concepts and the importance of being precise in your use of units.

So let's look at your two results.

You first said that someone would need 50,000 MBH per minute to meet there requirements.

That, as you admit, is incorrect.

But without seeing your working to tell where you went wrong, we can't tell what we need:

When she said 50,000 MBH per minute, which part do we ignore? Did our "engineer" mean that we need to generate 5,000,000 BTU per minute (MBTU/m) or 50,000,000 BTU per hour (MB/H). One takes 60 times as much power as the other.

So not a "minor booboo". It's the reason for this whole thread.

I had to give you something to find...

[transmitterdan]

Originally Posted by sailorchic34

You are correct. Its BTU per minute. A GPM time unit is not needed to calculate BTU per minute or to calculate BTUH. Done all the time from jsut a GPM number.

GPM is gallons per minute (gallons per unit time). There is no such thing as a "GPM time unit".

[sailorchic34]

Originally Posted by transmitterdan

GPM is not just a number. But it ain't volume either. It is gallons per minute. There is no such thing as a bucket that holds 5 gallons per minute.

The exact unit balanced equation you quote goes like this:

Q [BTU/minute] = Flow [gallons/minute] * (Tout-Tin) [F] * 1 [BTU/(lb F)] * 8.33 [lb/gallon]

units enclosed in []

The units of gallons, degrees F and pounds all cancel out to leave BTU/minute. There is nothing magic about it. It does not prove your argument that GPM is a measure of volume.

Agree with your equation, Sorry I was going by memory on the equation.

Hum Could not gallons per minute also be described in CFM. My simple mind relates gallons per minute to CF per minute. Both have a volume moved per unit time. It's why we can use 8.33 pounds per gallon with GPM as GPM has gallons which is a volumetric rate.

I probably should not mention that a 5 gallon bucket would hold 5 GPM for one minute.

[Paul Elliott]

Would you folks consider eventually returning to the electrical units discussion? Treating electricity as a flowing liquid in a pipe is a barely-adequate analogy at best.

And A/h (Amperes per hour) means rate of change of current, and in most cases is not a particularly useful measurement. It is most certainly not equivalent to Ah (Ampere hours).

[StuM]

Originally Posted by sailorchic34

Ah, sorry I'm an Autodidact, Never went to collage.

That explains it. An Autodidact frequently has large gaps in fundamental knowledge because they have never realised what they don't know. There is a reason that colleges teach to a syllabus rather than just letting students study whatever they want. If you had actually done the "Basic Engineering 101" which you keep referring to, we would probably never have started this thread.

Please forget about the distraction of "gallons" and re-read the original post.
Think about the basic concepts and try to understand the difference between quantity and rate. It's not hard - you can do it.

[sailorchic34]

Originally Posted by transmitterdan

GPM is gallons per minute (gallons per unit time). There is no such thing as a "GPM time unit".

Sorry getting a bit punchy responding to you all. You are correct. I should have said GPM is Gallons per unit time.

[transmitterdan]

Originally Posted by sailorchic34

I probably should not mention that a 5 gallon bucket would hold 5 GPM for one minute.

That sentence makes no sense from an engineering units standpoint. If you think it does then I'm out of ideas to convince you.

[fryewe]

Originally Posted by sailorchic34

I'm betting that in that 40 years as a EE you not once calculated a BTUH requirement from GPM.

If you are familiar with Nuclear Engineering, you should understand that the primary disciplines used are Reactor Dynamics and Thermodynamics, and operations require continuous evaluation and computation of convective and conductive heat transfer (under conditions with and without boiling), flow, head, head loss, gas laws, reactor physics, water chemistry...

But you are right about calculating BTU/hr requirements from gallons/minute...I never have...because on the face of it, it's an incomprehensible need. With inadequate knowledge of other more important parameters, such as temperature or enthalpy, and whether the delivery of the heat will be by convection, conduction, or radiation, or some combination of these, it's an incomplete question.

[Greatketch33]

Originally Posted by StuM

Many people get confused when discussing Amps, Watts, Amp hours and Watt hours. Frequently the confusion is the result of incorrect use of these terms by some forum posters. Hopefully the following will clarify rather than further fog the issue. First - A bit of background SI UNITS When we talk about a quantity or a measurement, we talk about a number of units. To avoid confusion between people, it is essential that everyone is "talking the same language". There is an internationally recognised set of Units called The International System of Units or SI which enables this. In the SI System, there are two fundamental types of measuring units: Basic and Derived Basic Units are simple things like length,mass and time.(the specific units for these are the meter, kilogram and second). There are several other such base units including the Ampere (for electric current) and the Kelvin (for temperature) Derived Units are more complex measurements which are formed by multiplying or dividing two or more different Base Units such as meters per second. For convenience, we often describe quantities in terms of non SI units such as horse power, gallons, nautical miles, knots or gallons per hour. Any of these units can be converted to their equivalent SI representation by multiplying or dividing them by an appropriate number. (Example: You can convert nautical miles to the SI unit "meter" by multiplying by 1852 and you can convert knots (nautical miles per hour) to meters per second by multiplying by 0.514444. 10 nautical miles = 18,520 meters and 4 knots = 2.05776 meters per second The Kelvin is a special case, it is exactly the same size as a degree Celsius, but with a different start point, so you can convert Kelvin to degrees Celsius just by adding a number and when calculating temperature changes, you can use the two interchangeably) DIMENSIONS The number of basic units used in a measurement is called the "dimensions" of that unit. So a meter or a nautical mile is a 1 dimensional unit (meters) and speed in meters per second or knots is a two dimensional unit (meters and seconds). Note that these do not have to all be different units: acceleration for example has 3 dimensions even though it only uses two different basic units, since it uses one unit twice (meters per second per second) Even more complex units such as the Volt can still ultimately be expressed in basic units. (The volt is actually a 7 dimensional unit which can be expressed as meters x meters * kg / secs / secs / secs / Amps ) A plain number by itself, without any specified unit is called "dimensionless" (i.e. numbers like dozen or 42). NAMES AND ABBREVIATIONS Unit names are frequently abbreviated. It is a convention that where the name of a unit comes from the name of a person, the name or abbreviation is capitalised, all other units are not. So we have Ampere, Volt, Watt and their abbreviations Amp or just A, Volt or just V and Watt or W, but meters (or m), seconds (sec or s), kilograms (kg), gallons (gal or g) etc As mentioned previously derived units comprise two or more units which are multiplied or divided by each other. A great deal of confusing arises where these operations are not expressed properly. When two units are multiplied together, the resultant unit name is written as the basic unit names without any intervening mathematical or other symbol. (i.e The commonly used unit of "energy" stored or used in an electrical system should always be written as simply Ampere hour (or Amp Hour, Ah). When one unit is divided by another , the two words are separated by a slash (divide sign "/") or the word "per" (or just p) (ie gallons/hour, gallons per hour or gph). FINALLY - AMPS, WATTS, VOLTS AND TIME There are a number of different aspects of electricity that we are concerned with: Current Flow, Force, Power and Energy The basic SI unit of electrical "current flow" is the Ampere (Amp or A). It is the measure of the rate at which current is flowing through a specific point in a circuit at a specific point in time. It is equivalent to the rate at which elementary electric "charges" are passing the point (charges per second) The derived unit of electric "force" is the Volt (V). It is a measure of the "potential difference" between two points in an electric circuit. The derived unit of electrical "power" is the Watt (W) It is a measure of the amount of energy flowing (Amps) through a point where this is a certain potential difference (Volts) across the point. So: Watts = Volts * Amps and Amps = Watts / Volts (Example: A solar panel generating 48 Watts at a point in time will generate a current of 4 Amps at 12 Volts or 2 Amps at 24 Volts.) Note that Amps, Watts and Volts are all measures of different aspects of electrical force at a single point in time. The final aspect of electricity above is "Energy" and this is where time finally rears its head. It is the amount of "work" that a given amount of electricity can do such as how long it can provide the required power (Watts) to a specific piece of electrical equipment and is expressed in Watt seconds. Rather than Watt seconds, it is more practical to talk about Watt hours (1 Watt hour is equal to 3600 Watt seconds) Also, if we are working with a nominal 12 Volt system, it is often easier to work in Amp hours where the voltage is assumed to be a constant 12V. Since Watts = Amps x Volts, 1 Amp Hour is, in this situation, the same amount of energy as 12 Watt hours (if we are working with a 24V system, 1 Amp hour is the same as 24 Watt hours) THE BOTTOM LINE. If we are working in Amps rather than Watts, then: The "capacity" of a battery, the amount of power used or needing to be replaced is a number of Amp Hours or Ah. It is not a number of Amps, Amps per hour or Amps/hr which as we see above are totally different things. There is no such thing as a 100 Amp battery. (Some batteries are rated in CCA or Cold Cranking Amps - but that is not an indication of its capacity, it is an indication of the maximum rate at which energy can safely be drawn from it ) There is no reasonable practical meaning of Amps/hr or Amps per hour (which is actually a measure of how fast a current is increasing or decreasing.) If we all use the correct units and abbreviations, we can avoid confusion and misunderstanding in our forum discussions. If we use them incorrectly, there is endless room for misunderstanding (and massive thread drift )

Hmmm.., yes I am no engineer and reading the debate in this thread I believe demonstrates -- to me anyway -- that confusion shall continue to be.

[sailorchic34]

Originally Posted by StuM

That explains it. An Autodidact frequently has large gaps in fundamental knowledge because they have never realised what they don't know. There is a reason that colleges teach to a syllabus rather than just letting students study whatever they want. If you had actually done the "Basic Engineering 101" which you keep referring to, we would probably never have started this thread.

Please forget about the distraction of "gallons" and re-read the original post.
Think about the basic concepts and try to understand the difference between quantity and rate. It's not hard - you can do it.

I actually understand the difference between quantity and rate. You can have 100 gallons and 100 GPM for 5 minutes. To different things, I get that. Yet just saying 100 gpm implies a rate duration per hour and a volume of flow in gallons. If I have 100GPM flowing I can calculate weight, mass, Btu's in minutes or hours, etc. Most of what I do engineering wise just uses GPM with no extra time units, such as GPM/minute or GPM/Hour. As most of what I do is GPM for 24/7.

I expect my knowledge has a few gaps. yet I've read pretty much every engineering text I could lay my hands on. That includes the ASHRAE books, ASPE and NFPA manuals and codes. Mind you I've not read all the chapters in the NFPA codes, probable only about half. Mind you I found high school boring and would have read all the books by the end of the first quarter.

[sailorchic34]

Originally Posted by fryewe

If you are familiar with Nuclear Engineering, you should understand that the primary disciplines used are Reactor Dynamics and Thermodynamics, and operations require continuous evaluation and computation of convective and conductive heat transfer (under conditions with and without boiling), flow, head, head loss, gas laws, reactor physics, water chemistry...

But you are right about calculating BTU/hr requirements from gallons/minute...I never have...because on the face of it, it's an incomprehensible need. With inadequate knowledge of other more important parameters, such as temperature or enthalpy, and whether the delivery of the heat will be by convection, conduction, or radiation, or some combination of these, it's an incomplete question.

I bow to your superior knowledge. There is some overlap (flow, head, etc) but lots more is going on in a reactor then say a gas or fuel oil boiler. What I don't know about nuclear reactor design would fill a room in books.

Yet for typical building systems, that is heating hot water and chilled water. It is quite common for engineers to calculate BTU/minute or BTUH via GPM, weight of water and delta T. This as the properties of water is for a single phase and within a narrow range of conditions. Steam is a bit different, though feed water is normally single phase.

Enthalpy comes into play with air movement and humidification, cooling tower design, etc. Not too much on the water side.

[sailorchic34]

Originally Posted by transmitterdan

That sentence makes no sense from an engineering units standpoint. If you think it does then I'm out of ideas to convince you.

Let me rephrase that. A 5 gallon bucket would hold the flow rate of 5gpm after 1 minute of duration.

Better?