Heat Pumps to heat water

[Leno]

Though the heat pump was installed last year, we only moved into the renovated house in June this year (yes, the renovations took exactly a year), and we've been using it as the sole source of hot water in the main house since then.

Here's a pic:

The geyser is an all-copper Tecron 200-litre 400 kPa specially modified by the Tecron factory in Cape Town.

I've set the water temp to 65 degrees, and the sytem off from 22h30 to 06h00. So far it's delivered on expectation. I don't have anything to compare it to as this was a total revamp in a house we've never lived in before. The system runs about 1.5 hours a day, drawing 1.1kW.

The system produced hot water throughout winter, and it gets cold here in the Little Karoo. Yes, it does use some electricity, but I reckon I'm using only a third or so compared to a normal kettle-element geyser.

It runs pretty quietly so can be installed above bathroom ceiling. Don't put it above your bedroom ceiling.

Happy customer. Contact Flying Hippo.

Edit. Reasons I went for this one rather than others:
* The engineering is done by a large local industrial heat pump supplier, Enerflow (supply to mines, hostels, hotels, etc) which is part of M-Tech Industrial. Their head technical honcho is an academic at Potch University, Dr Martin van Eldik, who wrote this paper comparing heat pumps to solar water heating.
* Locally supported. Spares readily available.

I have a thermostat wire from the panel connected to my geyser, could you tell me if you have one and which pipe they put it on?

[alphabyte]

Hi Leno,

...I checked out how the heat pump was retrofitted and i suspect that it was connected the wrong way

The heat pump OUTLET is connected to the geyser OUTLET along with the thermostat

The heat pump inlet comes from the T piece by the cold water inlet to the geyser...

According to the info supplied on one of the links - http://www.flyinghippo.co.za/information.aspx - it is correct that the cold water inlet goes to both the geyser and to the heat pump, and similarly the hot water outlets are connected together. In other words you draw hot water either from the heat pump or from the geyser in parallel. I don't know if the is actually correct, but it is what the diagram shows.

If you are getting cold water it could suggest that the thermostat control is faulty.

Please keep us posted, it would be interesting to know if and when the problem is resolved.

[3Gee]

The heat pump was R11K. My builder used his plumber and electrician to install.

what is the warranty period and any other terms and conditions for the heatpump

[Leno]

Hi Leno,



According to the info supplied on one of the links - http://www.flyinghippo.co.za/information.aspx - it is correct that the cold water inlet goes to both the geyser and to the heat pump, and similarly the hot water outlets are connected together. In other words you draw hot water either from the heat pump or from the geyser in parallel. I don't know if the is actually correct, but it is what the diagram shows.

If you are getting cold water it could suggest that the thermostat control is faulty.

Please keep us posted, it would be interesting to know if and when the problem is resolved.

I also suspect its the thermostat reading

They installed the external thermostat wire onto the output pipe, this is supposed to read the water tank temperature but it will read the water coming out of the heat pump not the water in the geyser...

2 of the readings on the panel are always the same, tank temp and outlet temp leading me to believe there are supposed to be 2 thermostat wires as those 2 values should be different

Anyway i turned the geyser down to 50 odd degrees an turned it on and shut off the heat pump, till the guys can come sort it out

[MegasXLR]

I also suspect its the thermostat reading

They installed the external thermostat wire onto the output pipe, this is supposed to read the water tank temperature but it will read the water coming out of the heat pump not the water in the geyser...

2 of the readings on the panel are always the same, tank temp and outlet temp leading me to believe there are supposed to be 2 thermostat wires as those 2 values should be different

Anyway i turned the geyser down to 50 odd degrees an turned it on and shut off the heat pump, till the guys can come sort it out

Don not run the geyser at 50 degrees for an extended period. very dangerous. Minimum should be 60-65 degrees. Google legionnaires disease geysers

Temperature affects the survival of Legionella as follows:[15]

70 to 80 °C (158 to 176 °F): Disinfection range
At 66 °C (151 °F): Legionellae die within 2 minutes
At 60 °C (140 °F): Legionellae die within 32 minutes
At 55 °C (131 °F): Legionellae die within 5 to 6 hours
Above 50 °C (122 °F): They can survive but do not multiply
35 to 46 °C (95 to 115 °F): Ideal growth range
20 to 50 °C (68 to 122 °F): Legionellae growth range
Below 20 °C (68 °F): Legionellae can survive but are dormant

[Leno]

Well the guys came today and moved the heat pump thermostat wire into the geysers thermostat hole. looks good so far the verdict will only be known for sure after tomorrow mornings shower time

[Gnome]

As others have said, these "heat pumps" are identical to air conditioners. Both are Carnot Heat engines and rely on the Carnot cycle. The difference between your common air conditioner and these "heat pumps" are that in your air conditioner a fan blows air over a radiator whereas the "heat pumps" used for heating water, move said water over the radiator (rather than air).

R11k is a total rip-off for a device not much different from an air conditioner. The only part that differs is the radiator and the control board that regulates temperature. Modern air conditioners also have much higher capacity than these "heat pumps" used for water. The amount of BTUs moved by a large 8kVA Air conditioner (approx. cost R8K) easily trumps a 1kW (1kVA) "heat pump".

All that said, the system is most efficient when the temperature coefficient is lower. The pictures above show the kind that exchanges heat from the primary loop working fluid directly with air by using a radiator (eg. heat is moved from the air surrounding it, by the heat pump, to the water you want hot). These are least efficient kind but because we don't have very low air temperatures in most of SA (at least inside our roofs) it might not justify the cost of the second kind. It is also advisable to install one of these in your roof (for efficiency sake) rather than outside because your roof maintains temperatures much better. In fact a well insulated home would be ideal but you would rob the house of some of it's heat.

The second kind uses a fluid (water combined with antifreeze) to cool the primary working fluid loop. That fluid (water + antifreeze) heats the radiator that was previously heated by surrounding air (remember it is the reverse of an air conditioner). Although it may seem less efficient because you have pump that needs to pump the water through the loop, the reality is the other kind usually use fans and those fans easily trump pumps when it comes to electricity usage.

In most countries like the US and EU they have below 0 temperatures during some parts of the year. There they have pipes underground because the temperature underground is a steady 25 degrees throughout the year.

But in SA we have seriously high temperatures on the roof of our houses in the sun. Ideally you'd want 2 loops. 1 loop goes on the roof and the heat is moved from your roof and when it is cold outside the heat is moved from pipes under your house.

As I said, heat is simply moved and the smaller the coefficient the more efficient a Carnot heater is (hence the lower you set the temperature the better the efficiency).

If it is below 0 for example, Carnot heaters can quickly become less efficient than the classic element based heaters (normal geyser). In very cold climates they sometimes make use of a combination of carnot cycle + element heaters.

[alphabyte]

the verdict will only be known for sure after tomorrow mornings shower time

Leno, have you had your shower yet...?

Thanks Gnome for your very informative response. I've also been wondering: if one uses a heat pump in combination with a normal geyser, then does it not make sense, contrary to what has been said earlier in the thread, that the outlet from the heat pump should feed into the inlet of the geyser? Then the heat pump can effectively pre-heat the water, thus saving the geyser a lot of work and electricity expense. The previous issue was that the 2 inlets are coupled and the 2 outlets are coupled - that somehow doesn't seem right? Any thoughts on this?

[Gnome]

Thanks Gnome for your very informative response. I've also been wondering: if one uses a heat pump in combination with a normal geyser, then does it not make sense, contrary to what has been said earlier in the thread, that the outlet from the heat pump should feed into the inlet of the geyser?

The reason for the geyser is to store the hot water. At 60 degrees Celsius I would simply disconnect the geyser power but unfortunately the examples above the geyser draws water from the heat pump and pipe. The good thing about geysers are that they are very well insulated so your temperature drop is in the order of 1 degree C every 5 hours, so it is a good place to store water anyway.

The example above of the unit installed outside is badly installed IMHO (inside one looks 100%). The outlet pipes should have insulation around them. Have you ever noticed that A/Cs always have insulation around some pipes? The same applies here. Thermally insulate the pipes on the outlet side. Even on the inlet side for a short stretch unfortunately heat will always radiate outward so the objective is to limit the amount of heat loss. Especially the picture with the unit outside, I can just imagine the amount of heat lost by that pipe.

The only part that shouldn't be sealed up is the vacuum breakers (plastic thingy that is on a pipe that comes out 30cm above the geyser) (one on the inlet and outlet side) and relief valves. They are a SABS requirement, insurance will also refuse to payout without them. The heat pump unit also seems to have some kind of pressure relieving pipe there.

Also ensure everything is situated under a drip tray, a plastic tub where water can drip and run outside or into a drain, etc (check the pic of the unit inside the roof). They are also an SABS requirement and hence insurance requirement. Except for externally installed units.

Then the heat pump can effectively pre-heat the water, thus saving the geyser a lot of work and electricity expense. The previous issue was that the 2 inlets are coupled and the 2 outlets are coupled - that somehow doesn't seem right? Any thoughts on this?

The most probable reason is that the heat pump cannot feed water quickly enough to the geyser.

If you don't have it, your water pressure will most likely suffer.

If you think about it logically: You turn on the hot water tap, the reason water flows out is because the water is under pressure. Water coming from municipality is under quite a bit of pressure. If you only connect the heat pump to the geyser and it cannot supply a high amount of pressure the water will flow much more slowly. Remember water like air is a fluid. Because the geyser is a sealed unit the water isn't being replaced by more water. If there isn't enough water, water will flow more slowly.

Only way to remedy the situation is to either install a breather pipe (so air, a readily available fluid can replace the water) or connect a feed pipe to the geyser. They chose the latter method and it makes sense, you don't want the geyser filling up with air the whole time and a breather pipe would also allow large amounts of heat to escape.

[Leno]

Leno, have you had your shower yet...?

Heya

Yep The shower is working MUCH better, the one shower which has one of those single selection handles for temperature and on off seems to have too much cold water pressure if its on full blast, but thats just a case of educating everyone here who tends to just open it up all the way instead of open it till the shower head is going full "speed"
(the shower head reaches full water "speed" only half way on the tap selector)

[Leno]

The example above of the unit installed outside is badly installed IMHO (inside one looks 100%). The outlet pipes should have insulation around them. Have you ever noticed that A/Cs always have insulation around some pipes? The same applies here. Thermally insulate the pipes on the outlet side. Even on the inlet side for a short stretch unfortunately heat will always radiate outward so the objective is to limit the amount of heat loss. Especially the picture with the unit outside, I can just imagine the amount of heat lost by that pipe.

Hmm thats exactly what i thought, can i just pop by builders warehouse and buy that white foam insulation?

Also tempted to insulate the hot water pipe that runs outside the whole house (they obviously didnt know you could run it in the roof when they built the house)

Thanks for all your info Gnome

[RoganDawes]

Heya

Yep The shower is working MUCH better, the one shower which has one of those single selection handles for temperature and on off seems to have too much cold water pressure if its on full blast, but thats just a case of educating everyone here who tends to just open it up all the way instead of open it till the shower head is going full "speed"
(the shower head reaches full water "speed" only half way on the tap selector)

You may want to investigate putting in a flow rate reducing device. It could be as simple as a washer (with a smaller diameter hole) in line with the cold water infeed. You'd probably need to experiment a bit to find the right degree to reduce the flow by.

[Leno]

You may want to investigate putting in a flow rate reducing device. It could be as simple as a washer (with a smaller diameter hole) in line with the cold water infeed. You'd probably need to experiment a bit to find the right degree to reduce the flow by.

Great idea thx, how hard are those shower mixers to open etc, im not much of a handyman when it comes to plumbing

would it be something i can unscrew off and back on, or something i will have "re connect" white tape and all!

[RoganDawes]

Unfortunately it might end up being quite complicated to fix.

You can't do it at the mixer typically, because they are sealed into the wall, tiled over, etc. And you can't do it at the shower head because it is already mixed at that point. You MAY be able to get to the cold pipe as it comes out the top of the wall, cut it open and insert a tap of some sort, but hope that it only feeds the shower, and not other water consumers (e.g the basin, toilet, etc), as they will also suffer a reduced flow. That may or may not end up being a problem.

Sorry I don't have better news.

[MegasXLR]

Great idea thx, how hard are those shower mixers to open etc, im not much of a handyman when it comes to plumbing

would it be something i can unscrew off and back on, or something i will have "re connect" white tape and all!

Best is to do it in the tap, the idea is to reduce the tap orifice, inspect one of the same taps at builders, they may even be able to give advice or call on a plumber.