Bear with me (and excuse any laxity in definitions, I said engineering not science 😉 )
I know what a kilowatt is, it is a definition of power output, basically 1000 joules (energy) converted into work (motion, heat etc) per second.
I also know what a kilowatt hour is, this is basically a conversion of power back into energy used, i.e. one kW for 1 hour is the same as 1000 joules being converted to work every second, for 1 hour (3600 seconds).
But what the hell is kW/h? To me this is like an acceleration, i.e. your boiler is increasing its conversion of joules to heat at a rate of x number of kW/hour.
I ask as we have received a gas mains capacity check from a major utilities company who express the mains capacity in kW/h. I'd assume typo but for a major firm who basically do nothing but gas I'd kinda hope they'd get something like that right...
nah, didn't help - deleted
Thanks Scaredy, that's just helping convert volumes of gas into kWhr I think.
Found a physics forum eventually, seems to confirm what I thought:
KW/hr has no meaning. It is just the way that the uninformed sometimes write kWh. Watts is Joules per second. I.e. power is energy per unit time. Saying kW/hr is like saying "energy per second per second" - a rate of power Increase. Barmy.
An example of this might the power ramp up rate of some power generating station. For example, a station that can generate 1 milllion kilowatts, but from a cold start, takes 4 hours to reach maximum power generation with a linear ramp up rate of 250,000 kilowatts per hour.
I used to be pretty confident in this sort of stuff, turns out 10 years working in building services can cause you to doubt even fundamental stuff you thought you knew 😕
kWh is as you say one kW for an hour, it's a unit of energy. Power (kW) is energy transfered per unit time, so kw/h is kilo joules per second multiplied by hours (or 1kWh is 3,600,000 Joules).
So kWh/h is actually just another way of saying kW, but in a way that make meter reading easy (it's how many units your meter can pass in one hour).
In other words, I'm pretty sure there's a 'h' missing, or they should have put a J not a W (and the number would be different), but I have seen kWh/h used before.
sorry, wot I posted was badly skimmed page after googling "gas main capacity kw/h"
kwh/h (so, kw then) would make sense but much dafter than cubic ft/hr
yes, but then ft3 is effectively a unit of power in this case, the calorific value of the gas is constant so there's a straightforward conversion between ft3, btu (1ft3 is 1000btu, or at least it is of 'natural gas', what's in the mains might be slightly different as it's standardised by diluting with nitrogen) and kWh, so it makes sense to then use ft3/h, btu/h and kWh/h.kwh/h (so, kw then) would make sense but much dafter than cubic ft/hr
Like you said, engineering, not science. Unlike science the units have to make sense in the real world! Hence we still measure volume in barrels on some projects!
Aha! Excellent, that makes sense, and in this instance what I wanted was to know the peak flow the pipe is capable of, i.e. in kW. So kWhr/hr would make sense, in a roundabout way.
The company in particular is an asset manager that would typically deal more with meters than pipes, so makes sense why they might use a number that relates to meters.
Like you said, engineering, not science. Unlike science the units have to make sense in the real world! Hence we still measure volume in barrels on some projects!
Ha, in my experience of building services units just become units 'by common usage'. In much the same way that 'selfie' and 'LOL' have made their way into the OED...
The capacity of the pipe would be measured in volumetric flow (m3/sec) and you would need pressure to calculate this.
Has has a calorific value (which the gas providers play with as it varies according to temperature) but normally sits around 39 from memory.
The output in terms of energy would be kWh but kWh/h would cancel out the time and you'd just be left with kW, which is power (max output). For example the max heat power of a boiler would be given in kW.
Thanks Wrecker, the utility companies we deal with seem to prefer kW as a measure of flow, which doesn't take the calorific value into account (i.e [i]x[/i] kW doesn't always equal [i]y[/i] m3/s) but I guess they take that into account when they advise on capacity.
Also as this is upstream of the meter we aren't privvy to the available pressure and allowable pressure drop so need to approach the network owners.
KW is not a measure of flow, is a measure of power. In this case, it can only be heat power which is essentially what you want. They will have calculated though, from pressure, pipe size and CV. Personally I would want to see their assumptions. You could also instruct a gas dude to take the static pressure and do the calcs. There is also a possibility of installing a gas booster set if it falls short of the requirements (which will be your heat loss calcs)
Beware boiler efficiency and other losses. Just because you have a main capable of delivering 200kW of heat, you won't actually get this from any system.
Yep, but in the particular area/bit of the industry I work in, pipe capacity is often measured in kW, as for standard/defined pressures and calorific values etc. flow can be calculated from kW.
It's not how I would do it either, but I guess in the real world people prefer to define the flow capacity of a gas pipe in the same units as the equipment they are connecting to it, so fair enough.
And yes, the ~3000kW peak capacity we require is gross (very gross, and it wasn't us who calculated it either, long story).
Flow can only be calculated if you have the things you say and pipe size. Otherwise where does the "m3" in "m3/s" come from?
Back to your original point! kW/hr is just a kW as its divided by 1.
1/1=1, 2/1=2 etc etc.
I think you're overthinking this Wrecker, the reason the number is given is because the utility company has a duty to supply domestic* customers with enough gas to run a house, i.e. sufficient kWh/h to run central heating, hot water, shower and cooker simultaneously. So in the context the unit makes sense, it's irrelevant what the pressure in the mains is, or its volumetric flow rate, the only thing that matters is that the house gets sufficient gas.
In the same way the water company has to provide a certain l/min at a certain pressure as it comes into your house.
*or commercial, but they would probably have their own agreements rather than the statutory ones for domestic consumers.
Yes and kW/h is just a measure of kW written awkwardly.
Utilities work in m3, that's what gas meters measure. They then calculate this to kW (call it kW/h if you like, same thing) via the cv. I have had to decipher enough gazprom bills!
The l/min in your example is dependent on pressure and pipe size.
KW/hr = KJ/s/hr = dimensional nonsense. Make sure you tell them it is nonsense, there are far to many people in this world being paid good money for spouting out nonsense 🙂
Yes and kW/h is just a measure of kW written awkwardly.
No kWh/h is kW written awkwardly.
kWh/h is just used because the conventional unit for energy when talking about domestic use is the kWh (3600kJ), so the unit of power becomes kWh/h, the point of knowing the capacity in kWh/h is because the mains in your street could be a few bar, it could be 10's of bar, it could be hundreds, so m3/h is meaningless, what you need to know is how many kW (or m3/h downstream of the regulator) an you get through your meter.
The problem is m3 in the mains will have no impact on m3 through the meter, so it makes the maths difficult, whereas if I have 100 houses, and need 50kWh/h per house, then I need a main that can deliver 5000kWh/h*, so if the mains was 100bar, then that would be about 4.5m3/h in the mains, and 450m3/h through the meters.
*you don't, because you can assume that not every house has a shower or the heating on at exactly the same time
Not for water, the density of that is pretty fixed, the GSS regs state a minimum flow and pressure at your boundary, i.e. there has to be enough pressure to get to the attic of your house and fill the tank as quickly as you could reasonably empty it. Although unlike gas, water isn't always regulated, you get whatever pressure you get.The l/min in your example is dependent on pressure and pipe size.
KW/hr = KJ/s/hr = dimensional nonsense. Make sure you tell them it is nonsense, there are far to many people in this world being paid good money for spouting out nonsense
Indeed it is, what on earth is a Kelvin Watt and Kelvin Joule?
kWh/h is just complete nonsense. It doesn't exist. The standard metric term for energy is kWh, be it gas, electric, whatever. Commercial or domestic. The OP mentioned kW/h, not kWh/h, which is complete claptrap. There is no such thing. Why the *** would you have kilowatthours per hour? Are the time measurement going to be different?
kWh is power x time, so are they using another measure of time, from a different dimension? Otherwise, the hours will just cancel each other out, and you're left with.......kW!
The problem is m3 in the mains will have no impact on m3 through the meter, so it makes the maths difficult
No it doesn't! Gas providers and the likes of Transco all work in pressure, not kW (as it varies as per the density of CV as per above). The pressure at the reg station needs to be above the sum of the requirements at the meters (taking into account pressure losses)
Low flow in water is either small pipe, or insufficient pressure, flow is dependent on these two things.
Scottish Water will guarantee 1.0 bar
of pressure at the boundary of your
property which is enough to fill a
10 litre bucket on the first floor of
your property in around one minute
*you don't, because you can assume that not every house has a shower or the heating on at exactly the same time
this is called diversity.
Indeed it is, what on earth is a Kelvin Watt and Kelvin Joule?
Quite! And now hard drives appear to be specified in TeslaBytes, i can't make head nor tail of it.
[url= http://www.energylens.com/articles/kw-and-kwh ]http://www.energylens.com/articles/kw-and-kwh[/url]
I found this useful as I needed to find a simple way of explaining it to building consultants for our stuff.
yes, but then ft3 is effectively a unit of power in this case, the calorific value of the gas is constant so there's a straightforward conversion between ft3, btu (1ft3 is 1000btu, or at least it is of 'natural gas', what's in the mains might be slightly different as it's standardised by diluting with nitrogen) and kWh, so it makes sense to then use ft3/h, btu/h and kWh/h.
As said by another poster - the above is not strictly true. It is true at a given temperature and atmospheric pressure. That's why there is a 'correction factor' applied to the calculation of energy used in kwh from meter readings in 'normal' connections (1.02264, I believe) or a Corrector fitted to meters for large and/or non-standard meter points.
Transco
Don't make me cry Wrecker. Those were the good old days... 😥
Don't make me cry Wrecker. Those were the good old days...
At least SGN aren't as bad as Scottish water, [i]they[/i] are a bunch of complete ****s.... 👿
At least SGN aren't as bad as Scottish water, they are a bunch of complete ****....
Tell me about it. I can forgive incompetence to some degree (I display occasional levels myself :oops:) but these guys have turned it into an artform. An artform which delays everything and costs other people huge amounts of money. In a manner which could only be realistically be explained by a deliberate desire to truly **** everyone over for no reason.
I hate them so much.
Its even better now that through WIRS we need to employ someone else to make the application on our behalf. I had one application which was knocked back as they were concerned about water quality with a joint water and fire main connection and advised separate connections. From the street. Which added another 150m of stagnant pipe. For each service. Our 'agent' hadn't the nous to go for a closer connection off the existing water main which would eliminate the additional 150m for the potable connection until I pointed it out... And yet [i]I'm[/i] not qualified to even make an application... 👿
And yes, they let it go right to the wire before making the connection. Think it took about a year from start to finish.
And breathe....
