Fridge that uses little, if any, of your battery!

[Uncle Bob]

Originally Posted by StuM

You are still demonstrating that you don't understand the basic difference between power and energy.

Watts are a measure of power i.e. the RATE of energy flow. There is no such thing as a "watt of heat". The phrase is meaningless. Are you talking about 1 Watt for 1 second or 1 Watt for 1 hour?

Watt hours (or Watt seconds or Joules or Calories) are the SI measures of heat. One Watt hour is the energy transferred in one hour by a power of one Watt which is 3600 Joules or 3600 Watt seconds.

To lower/raise the temperature of 1l of water by 1°C requires 4,200 Joules of energy. 4200 Joules is approximately 1.17 Watt hours (or 4,200 Watt seconds) So assuming you are talking about Watt hours, you are underestimating energy requirements by nearly 20%.

To freeze one litre of water at 0°C requires 334,000 Joules which is 334,000 Watt seconds or 93 Watt hours.
Can you provide a reference from RMIT that says the Watt is a unit of energy (or of "heat")?

Stu,a quick google yielded this from Wikipedia. "The standard unit for the rate of heat transferred is the watt (W), defined as one joule per second."

[StuM]

Originally Posted by Uncle Bob

Stu,a quick google yielded this from Wikipedia. "The standard unit for the rate of heat transferred is the watt (W), defined as one joule per second."

Absolutely correct. And that is what the OP doesn't understand. The key words being "rate" and "per second" (You may have noticed that I have said the same thing several times in this and previous threads)

Without a stated time, the rate of transfer tells us nothing about the quantity of energy being used.

Saying that a freezer uses 93 Watts per day is like saying you travelled at 10 knots per day, or that your engine burns 2 "gallons per hour" per day. Unless you know how long you travel or how long you run your engine, you can't say how many miles you cover or how many gallons of fuel you use.

If a rate of 93 Watts is maintained for a full day, the system will consume 2,232 Watt hours of energy. If the device only runs for 2 hours per day, the energy consumed will by 186 Watt hours.

To put it into basic terms, the rate of energy/heat transferred is an indication of power, not energy.
A 100 Watt light bulb will consume energy at a rate of 100 Watts. How much energy it uses (Watt hours) depends on how long it is switched on.
A 50 Watt light bulb is only half as powerful as a 100 Watt ligthbulb, but it will use the same amount of energy (Watt Hours) if it is switched on for twice as long.

[Off Trail]

Originally Posted by OzeLouie

Hi Dan, Yes it can be confusing but down under and in most of the world (except the USA and two other lesser countries) the metric system has been used for decades. Confusion is common specially when both Imperial and Metric are mixed together. Watts of heat (metric) replaces BTU's and is much simpler to work with as are most factors involved in metric calculation.

My factors quoted are common to the refrigeration industry and as I was taught during my apprenticeship and time at the RMIT. I only quote from my own hands on experiences and training but a search should provide you with confirmation of the factors I used.

OK, I'll take the poke at Americans and old units. We're an easy target. But.

I never mentioned BTUs, or any other imperial units. I am perfectly comfortable in metric. In the SI system the Joule is the unit of energy, while the watt (representing 1 Joule per second) is a RATE of energy transfer.

Thus to say it take X number of watts to raise some amount of water by a delta T is just incomprehensible. X watts transferring for 10 hours is 10 times the energy of X watts for one hour.

Do you mean watt-hours when you are saying watts? Is this a colloquialism in the refrigeration industry? That I could understand, like folks using amp-hours for electrical energy where the 12 volts are understood from context.

If so you would be better served in making your arguments using standard units.

Can you please confirm? When you say watts you mean watt-hours? A lot of this thrash could go away if this could be clear.

Dan

[Adelie]

Originally Posted by more

Electricity is measured in Watts and kilowatts
Electricity is measured in units of power called Watts, . A Watt is the unit of electrical power equal to one columb/amper under the pressure of one volt.
ampere ampere-hour is old terms for Columb units by measuring the electromagnetic force between electrical conductors carrying electric current.
The ampere was then defined as one coulomb of charge per second
The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge. Under the 2019 redefinition of the SI base units, which took effect on 20 May 2019,[2] the coulomb is exactly 1/(1.602176634×10−19) elementary charges.

when somebody tell me my light spend day 2 amps don't mean anything, what because in citation only thru is 1 day 24 hour. other is all xx.
most important in formula missing constant voltage and current Columb.

Do you understand how long is my boat if I tell you my boat is long 50 feet of my father's winter boots?

again if somebody tells me he on frige spent in day 1000 watts hour I understand how much need energy to recovery/calculates loose. not matter system is 12,24,220,1000 volts

Watts are defined as "the SI unit of power, equivalent to one joule per second, corresponding to the power in an electric circuit in which the potential difference is one volt and the current one ampere." Watts are a rate of energy transfer.

Joules or Watt-sec or Watt-hr are inter-related units of total energy.

Amp-hr are a measure of coulombs. If there is an implied voltage such as 12v then they are a proxy for total energy.

[Richard Kollmann]

Originally Posted by rgleason

Dockhead

I agree, but now using the efficient Danfoss compressor systems there is lower maintenance due to the fact that there is no leakage of refrigerant from the belt driven compressor.

Mr. Kollmann,
I have referred to your refrigeration manual and it was helpful when I started to learn, but you should open your mind to the fact that all boats and situations are not the same.
Eutectic was absolutely the answer for our boat and it has served very well for many years without having to change our battery system significantly.

Perhaps you should create your own thread and post there rather than creating another situation where the moderators have to step in, which is where you are headed. I still answer questions on email and follow threads on this forum

I am going to suggest to the moderators that perhaps this thread should be frozen now so that the information is not lost.

I am a believer like you in eutectic energy storing plates when justified. There was a time when hundreds of blue water boats around the world had my designed systems and eutectic plates. At 87 and alone I have many good memories of mostly sail boaters Like Andy sailing around the world with family, Jack and sue aboard Blaze who sailed from England to Florida on 26 ft boat not equipped with any electrical power nav lights were oil burning flame. They upgraded two boats with my refrigeration and hybrid plates and sailed Blaze to south Australia. Another interesting friend French wood carver with a machine wood working shop on a 30 ft sailboat, a friendly boater who avoided a FBI most wanted list till he ordered repair parts for his boat, and there was Sailboat Charlie's 63 foot three master 20 years to build cabled to the 79 interstate bride in Pittsburgh PA that made it down river to the Gulf but could not sail or motor across the Gulf Stream.

I stopped the printer from producing more of my books, My web Forum is shut down and My web site will never be changeable and when the Domain expires it will be gone. I still answer my email and follow threads on this forum....

[RaymondR]

That's a pretty good record Richard.

We would avoid a lot of confusion if we just stuck to BTU,s.

Whilst the metric system does a pretty fair job of contriving derived units from fundamental in the instance of refrigeration it tends to wander a bit far from what is readily perceived by observation and experience and it all gets just too damned abstract.

[StuM]

Originally Posted by RaymondR

That's a pretty good record Richard.

We would avoid a lot of confusion if we just stuck to BTU,s. .

Yeah, right - thereby doing all of our calculations in lbs of water and degrees fahrenheit

And then we get all those people who should know better talking about the power of a gas burner or an aircon in BTUs when they actually mean BTU/hr (aka BTUH ). That one is much more common than the confusion between Watts and Watt hours!

(For those who are interested, 1 BTU is an amount of energy roughly equal to 0.3 Watt hours and 1 BTUH is a measure of power equal to roughly 0.3 Watts)

[triibutu]

Maybe it would help if the OP or anyone could provide a reference to a formula to convert from *BTU*'s to *watts*?

[StuM]

Originally Posted by triibutu

Maybe it would help if the OP or anyone could provide a reference to a formula to convert from *BTU*'s to *watts*?

Impossible to do directly, they are measuring two different things.
That's like asking to convert knots to kilometers. (or more accurately, converting miles to kph)

You need to include a time dimension as well for any sensible formula.

[triibutu]

Originally Posted by StuM

Impossible,

Killjoy

[OzeLouie]

Originally Posted by triibutu

Maybe it would help if the OP or anyone could provide a reference to a formula to convert from *BTU*'s to *watts*?

Google it!
https://www.olimpiasplendid.com/btu-...ly%20by%203.41.[/URL]

[triibutu]

Originally Posted by OzeLouie

Google it!
https://www.olimpiasplendid.com/btu-...ly%20by%203.41.[/URL]

That page talks about how tio convert BTU/h to watts. I don't see how to convert BTU to watts?

If the distance between two ports is 20 kilometers, how many knots does it take to get from port A to port B?

[RaymondR]

Originally Posted by StuM

Yeah, right - thereby doing all of our calculations in lbs of water and degrees fahrenheit

And then we get all those people who should know better talking about the power of a gas burner or an aircon in BTUs when they actually mean BTU/hr (aka BTUH ). That one is much more common than the confusion between Watts and Watt hours!

(For those who are interested, 1 BTU is an amount of energy roughly equal to 0.3 Watt hours and 1 BTUH is a measure of power equal to roughly 0.3 Watts)

A BTU is the amount of heat required to increase the temperature of one pound of water by one degree of fahrenheit.

Now whilst this may not be able to be reduced to the fundamental units of mass, length and time etc. the BTU is readily intellectually grasped and more effectively differentiates amounts of heat from temperature. A concept often difficult to grasp by those with no science education.

So the BTU is not a unit of power, although various conversions can be applied, it is a statement of an amount of heat readily measurable.

For example one could place 10 pounds of hot water in your fridge and measure the temperature decrease of 10 degrees F and know the heat loss is 100 BTU, it's very easy to remember and carry out a calculation bases on 1, 1, 1.

[triibutu]

Originally Posted by RaymondR

A BTU is the amount of heat required to increase the temperature of one pound of water by one degree of fahrenheit.

This is as much true as that it only takes 0.1 watts (or less) to increase the temperature of one pound of water by one degree of fahrenheit.

[StuM]

Originally Posted by triibutu

This is as much true as that it only takes 0.1 watts (or less) to increase the temperature of one pound of water by one degree of fahrenheit.

Very true.
And it's equally true that it may take 1000 Watts or more to do the same thing. It all depends on how quickly you want to do it.
Since 1 BTU is very close to 0.3 Watt hours (0.293 to three decimal places). 0.1 Watts would take 3 hours to do it.



How easy is it to work out BTUs if you are using non-SI fluid measures such as US gallons (8.34lb) ?