1. Originally Posted by atomcrusher
I'm sure it must be about right, but to me it sounds like making 3 x 1kg loaves of bread from 1kg of dough
3 kg of dough may make 3 x loaves, but each loaf would surely weigh only about 333 grams

I'd still like to find a scientific & unbiased explanation for the seeming tripling of energy
They don't generate heat.
They transfer heat from one location to another. They compress gas, which heats it up. This compressed gas is fed into a radiator effort thing, through which air blows and is warmed up - thus heating the room.

The gas is then allowed to expand again, at which point it cools down significantly. This colder gas is passed through another radiator outside, and ambient air is used to warm it up to outside temperature again. And the cycle is repeated.
The energy cost is in pumping the gas around, NOT in generating the heat, which is simply transferred from one location to another.

They don't generate heat.
They transfer heat from one location to another. They compress gas, which heats it up. This compressed gas is fed into a radiator effort thing, through which air blows and is warmed up - thus heating the room.

The gas is then allowed to expand again, at which point it cools down significantly. This colder gas is passed through another radiator outside, and ambient air is used to warm it up to outside temperature again. And the cycle is repeated.
The energy cost is in pumping the gas around, NOT in generating the heat, which is simply transferred from one location to another.
Ok .. this is starting to make a bit more sense .. but
This colder gas is passed through another radiator outside, and ambient air is used to warm it up to outside temperature again
What happens when the ambient outside air is cold, as in winter?

Let's assume the water in my geyser (which is insulated, and situated in a roof space that is warmer than the ambient outside temperatures) is at 20C, and the outside temperature is much lower, say for example 10C.

How does the heat pump extract heat out of cold outside air, and transfer that extracted heat, and heat it up to higher than the existing geyser temp of 20C?

3. ## solar geyser

Remember there is also phase change involved- ie gas to liquid and liquid to gas, which involve significant amounts of heat energy.

When it's very cold outside, the efficiency of the system is reduced somewhat, but the temperature differentials we are talking about are a lot bigger than ambient fluctuations. Even when it's -5 outside, my heat pump aircons can warm the room up, because the expanding gas in the outside evaporator is a lot colder than -5 and so it is still warmed up by the outside air.

4. Originally Posted by The_Mowgs
Mike, if I may ask, what did you pay for that system? Currently we will only be 2 occupents in the house so do you think I should rather buy a smaller one?
We're using a 200L for three. For two 150L is sufficient. It does depend how much hot water you use.

5. ## solar geyser

Originally Posted by noxibox
We're using a 200L for three. For two 150L is sufficient. It does depend how much hot water you use.
And if it don't stay just 2? If your family is established, all good. Else get bigger.

6. hi guys

just a quick question. had a look at the solar geyser installation yesterday just a routine check up. all is fine except the new 200kpa PRV on the in coming mains they installed is dripping continuously. so I queried this with them and they say its supposed to drip?

now I can understand if the main pressure exceeds 200kpa then it may drip but continuously 24/7?

I just a bit concerned although its about a drip/sec over a month / year it can add up to a lot of wasted water?

am I missing something here or what?

7. Originally Posted by spiff
hi guys

just a quick question. had a look at the solar geyser installation yesterday just a routine check up. all is fine except the new 200kpa PRV on the in coming mains they installed is dripping continuously. so I queried this with them and they say its supposed to drip?

now I can understand if the main pressure exceeds 200kpa then it may drip but continuously 24/7?

I just a bit concerned although its about a drip/sec over a month / year it can add up to a lot of wasted water?

am I missing something here or what?
If something dripped constantly, and the company told me it was supposed to (barring temperature relief and pressure relief valves), I would tell them to come and take their crappy product away...

8. Originally Posted by ToxicBunny
If something dripped constantly, and the company told me it was supposed to (barring temperature relief and pressure relief valves), I would tell them to come and take their crappy product away...
sure but its not there product. its a standard pressure valve that I asked them to replace as the old one started leaking as soon as they reconnected it. so they went and bought a new off the shelf 200kpa PRV @ R500 and installed it. none of their equipment is leaking.

I just want to be clear on what should or should not leak. as I don't see why it should be leaking barring sudden pressure increases over and above 200kpa from the municipality.

9. guys is there any advantage / disadvantage in installing a 2nd solar panel?

10. Originally Posted by atomcrusher
Ok .. this is starting to make a bit more sense .. but What happens when the ambient outside air is cold, as in winter?

Let's assume the water in my geyser (which is insulated, and situated in a roof space that is warmer than the ambient outside temperatures) is at 20C, and the outside temperature is much lower, say for example 10C.

How does the heat pump extract heat out of cold outside air, and transfer that extracted heat, and heat it up to higher than the existing geyser temp of 20C?
A heatpump is very similar to a deep freeze in reverse. The compressor extracts heat from the food in the freezer, and releases it in the coil at the back of the fridge (feel it, it is hot). So just imagine your freezer compartment as the cold part of the heatpump in the ceiling/outside and the hot freezer coil as the coil inside the heatpump that is heating your water. Even when your freezer is at -15C, it can still remove more heat from the food and chill it further. So even if the outside temp is below freezing, the heatpump can still extract heat from the air and transfer it to your hot water. The efficiency is dependent on outside temperature, so the warmer is is outside, the less energy and time it takes for the heatpump to heat your water.

Temperature is just molecules vibrating, so it doesn't matter if the outside temp is less than the water temp. The heatpump can still extract energy from those vibrating molecules (they just vibrate less..) Only living things experience temperature as "hot" or "cold".

A deep freeze is like 150 Watts, while a heatpump is 1000W or more so it works much quicker than a deep freeze.

An air conditioner, on the other hand, can operate in both modes. To cool, it is like a fridge, extracting heat from the room and sending it to the hot coils outside your house. To warm your room, it acts very much like the hot water heat pump, extracting energy (heat) from the air outside and sending it into your room.

The reason a heatpump saves electricity, compared to an electic element geyser, is because all the energy is used to run the compressor only, which is compressing the refridgerant liquid. It is not doing any work to actually "heat up" the water. The heat comes from the air. With a geyser, all the energy is used to heat up the element, which then heats the water. This is how you get a 3kw heating capability, from just 1kw of electricity. An aircon is also efficient like this.

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