Heat pump hot water systems

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jonescg
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Heat pump hot water systems

Post by jonescg » Tue, 06 Aug 2019, 21:33

So I just got one of these installed!
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The sparkies wired it up this afternoon, so I turned it on and hit the boost feature (an electric resistive element which heats the top 150 litres to 60'C). The compressor was running at the same time, so it pulled a full 4.5 kW single phase. Within 4 hours the water was hot enough for two showers and no water saving shower heads. As soon as it hit 60'C the element turns itself off and the compressor continues to run. As long as the ambient temperature is between 7'C and 35'C it will get the water up to 60'C without needing to use the element.
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I'll keep an eye on the energy consumption over the next few days, but it looks like it should only consume about 4 kWh a day. Easily met with a half-dozen solar panels on the roof.
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T1 Terry
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Re: Heat pump hot water systems

Post by T1 Terry » Wed, 07 Aug 2019, 09:07

I've heard many complain that when the compressor packs it in it can't be fixed as parts are not available.

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antiscab
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Re: Heat pump hot water systems

Post by antiscab » Wed, 07 Aug 2019, 09:10

Is that a midea unit?

If so, I have an older model.
I actually disconnected the boost element, after a housemate who loves hour long showers kept setting the unit to boost only.

Boost only heats up the top half of the tank, and only starts heating when you have used more than half of the hot water.

Does yours have the fan at the back?
I'm surprised it was installed so close to the wall

I highly recommend insulating the pressure valve and pipe.
The ata sells a snap on insulated cover that does the job really well (I used my Flir to check)

To prevent corrosion issues, pipe the condensate away from the unit somewhere. On humid days the unit can generate 5-10L a day. I ended up using a rain water tank to collect it all
Matt
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antiscab
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Re: Heat pump hot water systems

Post by antiscab » Wed, 07 Aug 2019, 09:11

If the compressor packs it in outside of warranty, you can still plumb in an external unit.
Matt
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Re: Heat pump hot water systems

Post by jonescg » Wed, 07 Aug 2019, 11:07

Interesting - I had this particular unit recommended by Neil at Albany Solar. If parts fail I do have a warranty, so hopefully that's covered. As Matt says though, you can no doubt plump an alternative unit up to it.

There is a setting which allows you to disable the element, and you can set it so the compressor only runs during daylight hours. So I will have a play with it in the afternoon.

I don't recall seeing a fan at the back. Maybe it's at the top somewhere?

I have already redirected the condensate pipe away from the cement slab - I noticed it was running underneath the unit and I thought, yeah that will rust in no time. Good call on the insulation on the valve too. Copper pipe conducts heat away very effectively.
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Re: Heat pump hot water systems

Post by antiscab » Wed, 07 Aug 2019, 14:53

it seems they stopped making the valve cosy:
https://shop.ata.org.au/shop/valvecosy- ... alve-cover

My midea unit is the smaller 170L unit

The larger unit (or maybe your's is from a completely different manufacturer) may have the fan pointed upwards

I've been looking at making an enclosure for the bottom portion of my HWS, so all the cold air it pumps out doesn't settle around the tank
I'll probably get around to it in the next few years :lol:
Matt
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Re: Heat pump hot water systems

Post by jonescg » Wed, 07 Aug 2019, 14:57

Yes sorry I forgot to mention it is indeed a Midea 280 litre unit. I presume the heating element can be disabled with the right setting, likewise the compressor can be tuned to run while the sun shines - important considering we mainly shower at night.
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Re: Heat pump hot water systems

Post by antiscab » Wed, 07 Aug 2019, 15:03

if the control logic is same as mine,
you can set it by time. one "turn on" time per day and one "turn off" time per day

I have mine so it's off between 4pm and 9pm, and on the rest of the time (compressor only, I'm on the old smart power, where peak expensive time is 0700-1100 and 1700 - 2100)
would be nice to have it auto turn off 0700 - 0900 or so, but my solar usually ramps up in time
Matt
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Re: Heat pump hot water systems

Post by adam lippiatt » Thu, 08 Aug 2019, 17:57

Cool post re heat pump. I have very old gas HWS which still keeps on going, but once it finally dies I will look out for a heat pump and cut off the gas connection.

I am on the old smart power too - so would like a system that can run with the sunny shoulder and off peak times for boost if needed.

From time to time I go looking for a heat pump that can dump its cold reject air in summer into the house (and eject it outside in the winter time). The extra complexity / cost might not be worth it?

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Re: Heat pump hot water systems

Post by jonescg » Thu, 08 Aug 2019, 18:21

Yeah likely to be not worth it, but I'll have to see how much 'coolth' there is in the heat of summer.

For reference, this 280 litre unit cost $3000 installed, after the STCs were deducted. Which is pretty good I reckon.
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Re: Heat pump hot water systems

Post by adam lippiatt » Thu, 08 Aug 2019, 19:10

Thanks for letting us know -I think that is a good price from my past searches into this. I used to think that roof top passive solar was the way to go but I think that these days, for less fuss if you aren't doing a new build, heat pumps are the way to go.

The insulation looks like a good job (ex the pressure relief valve). I had an air conditioner installed and the insulation on the piping was terrible and perished in the sun in a couple of summers. Mostly fixed now - but I wish I had had an eye for those things at the time.

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Re: Heat pump hot water systems

Post by T1 Terry » Fri, 09 Aug 2019, 09:10

We built a system when back in the Illawarra region (NSW) that used a stainless tank with 2 inlets and 2 outlets. The normal cold water in at the bottom and hot water out at the top, but also 1/4 of the way up the tank, another outlet and roughly half way up the tank an inlet. The middle inlet and outlet were connected to a recirculation pump that was connected to an evacuated tube heat exchanger solar tank on the patio roof. There is a sensor port between the recirculation inlet/outlet in the storage tank and a second sensor on the heat exchanger tank.
The controller looks at the differential between the two temps and starts the pump when the differential reaches 12*C and stops when it drops to 5*C. I also added a low voltage heating element into the bottom of the tank and shunted the solar to that once the batteries reached 90% SOC and turned off at 75% SOC.
With 5 adults in the house, 3 of then teens who showered twice a day for what ever reason, but we rarely ran out of hot water. Once they moved out the system more than covered our hot water needs so we plumbed the washing machine in to accept warm water rather than cold and heat the water itself (earlier dumb type front loader machine with a single water inlet).
We had two circulation pumps fail in 7 yrs it was working there and when we moved I pulled the whole lot out and brought it to SA with us. One day I'll install it at the house, and a battery pack and inverters and lots of solar, just need that 8th day each week so I have the time available :lol:

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Re: Heat pump hot water systems

Post by jonescg » Fri, 09 Aug 2019, 09:21

Yeah diverting excess sunshine to water heating is such an easy thing to do, and not having >300 kg of mass on the roof is a good thing too. Solar PV is so cheap now that you can easily manage hot water with electricity sourced from the sun, even better if you are using a heat pump (the main motivation for getting this, and replacing the old SHW collector). With that thing off the roof, I now have room for almost 9 kW of solar.
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Re: Heat pump hot water systems

Post by antiscab » Sat, 10 Aug 2019, 07:30

My smaller unit was $2000 installed after stc were taken off.

I bought it mainly to reduce my winter time energy needs, as compared to my old electric storage unit
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Re: Heat pump hot water systems

Post by jonescg » Mon, 12 Aug 2019, 15:37

Had a minor hiccup on Saturday with the breaker tripping and refusing to reset. I turned the HWS off at the isolator and still couldn't reset the RCBO. Called the sparky who came out a few hours later... and reset it with no difficulty at all. Either it's an overly sensitive breaker or there's some minor leakage somewhere. Seems to be fine now.
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Re: Heat pump hot water systems

Post by antiscab » Mon, 12 Aug 2019, 20:14

Condensate? Sat was warm and sunny, it could have evaporated off in the time it took the sparky to come out.
Matt
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Re: Heat pump hot water systems

Post by jonescg » Mon, 12 Aug 2019, 21:49

Possibly - I feel like it really needs to be under cover somehow. The top cover can get very dewy.
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Re: Heat pump hot water systems

Post by jonescg » Tue, 13 Aug 2019, 08:20

Also, I wonder what the temperature read-out is - it claimed to only be 34'C, but when I ran the tap it was well over 50'C. Maybe it refers to the mid-tank temperature?
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Re: Heat pump hot water systems

Post by antiscab » Tue, 13 Aug 2019, 14:03

yep, that's the temp in the middle of the tank.

I've been toying with the idea of putting a temp sensor every 10th up the side of the tank so I can get an idea of how much hot water is left

the compressor heats top down too, so target temp is likely exceeded at the top of the tank (though the tempering valve sorts that out)
Matt
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Re: Heat pump hot water systems

Post by Richo » Thu, 15 Aug 2019, 12:33

jonescg wrote:
Mon, 12 Aug 2019, 15:37
.. the breaker tripping and refusing to reset. I turned the HWS off at the isolator and still couldn't reset the RCBO.
You'd think if the isolator isolated the HWS the RCBO should be happy.
Did the sparky check the isolator?

I have a gas HWS that is due for replacement.
I have a giant ducted reverse cycle A/C that spits the dummy every couple of years.
Usually costs me ~$1,000 in repairs.
So I'm reluctant to go buy a HWS that has a similar setup - compressor, gas etc...

I'm tempted to shove in some peltiers...
So the short answer is NO but the long answer is YES.
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Re: Heat pump hot water systems

Post by jonescg » Thu, 15 Aug 2019, 13:08

The isolator only switches the active, neutral has to remain connected at all times. Its possible that there was condensation inside the hot water system itself and there was a path between neutral and ground.

Isolator was fine - dry and no daggy strands.

A resistive HWS is also fine if you have enough solar to make up the difference. Usually roof space is not in short supply in Perth.
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Re: Heat pump hot water systems

Post by doggy » Thu, 15 Aug 2019, 13:52

Hi Richo,
Peltiers are so inefficient.
I built my own Solar HWS from evacuated tubes, using a standard (non solar) HWS tank in 2011. Total cost was <$2000. Did not bother with STCs.
Performance over 8 years has been brilliant (in Sydney, suboptimal 70deg Azimuth, lots of huge trees).
Totally exceeded all my (and family) expectations.
Commercial quotes were ridiculous rip offs but I assembled mine from parts (including mounting frame) from a reputable supplier still in business years later.
8months absolutely zero boosting per annum even with cloudy days.
Occasional boosting (elec offpeak) cost a handful of dollars for each year.
Solar controller makes it all work including preventing the tank reaching over 70deg which would damage the glass lining.
315L tank on the ground. Circulating pump about 20W discontinuous.
Clever bit of plumbing gear from the supplier ensures the return HW from the roof comes in about one third up the tank.
Only about 5weeks around the winter solstice when the temp does not exceed 60deg so Legionnaires not an issue.
Because tubes are 90% efficient AND self tracking because of the shape, less roof space is used than for a PV+heat-pump solution [until we get 30+% efficiency PV panels].
I still have two spare tubes but look like never using them despite hail storms etc.
Way few moving parts. The ONLTY issue I have had was this year when the special valve at the highest point got a little stuck and started dribbling at the start of each day. I replaced it, but the problem was simply calcium deposit build up which I removed from the old one by soaking in vinegar. So now I have a spare valve.
Cheers,
Dave

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