Gas HWS or Heat Pump HWS

[LanceC]

We put in a Dux heat pump hot water system when we built our house about twelve years ago and it was terrible. The heat exchanger frequently froze up over winter which meant it couldn't provide hot water, it was noisy, talking to Dux was an exercise is futility. All in all a really bad experience.

About three years ago it died after getting too much rain on it during a wild storm, and we replaced it with a Sandon split system unit. Night and day difference. It is, for all intents and purposes, silent. It uses what I think is a miniscule amount of power. I just checked... 2.5 kW yesterday in the Tasmanian winter, and it was raining all day. This is for a five adult household. It only needed to run for 2.5 hours.

We recently considered solar to offset or heating costs, but with it this cheep to run, the economic argument just isn't there in our situation.

[Grumpy John]

Thank you all so much for your input, it is really appreciated. Heat pump technology has certainly come a long way since the '90's and it seems to be the way to go. From what I understand most models allow you to set a timer so that the heating element (if required) does not come on during the night when there is no solar to offset any electricity being used to heat the water.
I still like the idea of the instantaneous systems, but there is no rebate on them and the cost + installation would put it in the $1000+ area.
As I stated in my OP the current storage HWS is 7 YO and the average lifespan of them is 7-10 years so I'm thinking that I should do something while the rebates are still available.

[Chris Parks]

If you were looking at running an electric storage heater off solar you would want to make sure you have plenty of excess solar capacity, I think the heaters are 3.6 or 4.2 KW that will be getting drawn from your system plus you are buying electricity to run the boost side of things when the sun don’t shine.
I am a bit out of touch with these as they were not allowed on new house builds until recently as they didn’t meet BASIX requirements

The input does not have to be the rating of the elements and is usually less and can be configured for how much goes into the HWS with a cutout if the solar output is not sufficient. Using off peak the savings can be good and most find that on the average very little off peak gets used, it trickle charges so to speak. The aim with solar these days with reduced and soon to be none feed in tariffs is to use or store all the production on site. Already some power suppliers are limiting export from solar systems due grid problems but that is a different topic altogether. My FIT is the same as my off peak rate so it is a bit of a wash for me at the moment.

[Grumpy John]

Here are a few details I omitted from the OP.

My energy supplier (Momentum Energy) does not have peak/off peak/shoulder rates. They have a sliding scale rate:

First 11.1781 kWh per day: 22.15¢
Balance per day: 23.63¢

And some good news from Momentum:
NOTICE: Applicable feed-in tariff to change from 1 July 2021

Your solar feed-in tariff is reviewed each year. From 1 July 2021, the minimum feed-in tariff rate set by the Essential Services Commission is 6.7c per kilowatt hour. This means your applicable feed-in tariff will decrease from 10.2c to 6.7c per kilowatt hour.

[yvan]

MrBush, we've had a Sanden unit for the past eight years with no regrets whatsoever.
Very efficient and the unit is almost silent.
Our system will switch off when the filter gets dirty. Apparently we have old pipes supplying our abode...
I now flush the unit every six months or so - as per instructions supplied - before it does it on its own!

Our power consumption is in the order of $30-35 per quarter.

Cheers,
Yvan

[Mr Brush]

Hi Yvan,

The builder who rebuilt our house only uses Sanden, and they are doing work on some multi-million $ properties in this area - ours was a very modest build by their standards. Not the cheapest, but the stainless steel tank won't need replacing in my lifetime (plus we have the tank under cover in the garage, compressor unit in a sheltered outdoor services area).

Very happy with it so far, MUCH quieter than the Quantum heat pump HWS we had previously, and no shortage of hot water. I just need to get into the programming to set it up to only operate when we have power from solar, i.e. only run from 9.00am through to 4pm. Our solar system is generating about 30kW/h per day total even in winter with the sun lower in the sky, so essentially we'll have free hot water. I note your comment about cleaning the filter, and I'll delve into the manual for more info.

Cheers

[yvan]

MrBush, what drew us first to the Sanden is the fact that the gas is CO2.
We also selected the slim & tall cylinder rather than the fatter squatter option.

Happy campers!!!

Cheers,
Yvan

[Mr Brush]

Yes, the Sanden was the only heat pump HWS I could find with CO2 refrigerant, which works better in cooler climates (I'm in NSW southern highlands).

The old unit we had was one of these all-in-one setups

How Does it Work – Quantum

but the (potentially flammable) refrigerant they use now means the whole unit has to live outdoors.

[yvan]

For Grumpy John!

I'm afraid I don't know how to rotate the pics the right way...

Cheers
Yvan

[Optimark]

I read this thread when it was started, and as things have been added by people. I have been thinking about replacing our 30/32 years old Aquamax stainless steel gas unit as rust is starting to get quite obvious around input and output pipes on the tank. Not to mention there is no way you can read any of the instructions to work the gas, everything has faded.

We also had a water pipe leaking somewhere under the house in a couple of places. All replaced with plastic pipe, fast and cheap and should see us out. When the water was back on, the plumber tried for a long time to get the gas pilot to work. He got it working by adding heat from my hot air gun on the housing surrounding the pilot light and suggested I should start looking at a replacement HWS as some of the parts were close to carking it.

To that end Ive been looking at changing to electricity for the HWS and using some kind of heat pump system as a possible contender. So far the Sanden is always at the top of the list for every parameter. But, and there is always a but, what are the possible issues?

I read about water filters clogging up and requiring a service call, especially on the earlier units. This appears to be a true issue and was partly caused by the heat exchange unit being horizontally mounted. This was in the G2 2011 model for sure and may also have been in the G3 model. By 2018 the G4 model (current) was released and the heat exchange unit in that is vertical and apparently has fixed the sludge in the pipe issue which I suspect was the cause of the filter(s) blocking.

I also heard about the units coming on in the middle of the night in winter when it is cold and in some instances staying on for quite some time. This is true, but with the current G4 unit there is a defrost function which is tripped when the ambient goes below 3ºC and the unit goes into preservation by having a defrost for about 10 minutes to raise the compressor/heat exchange unit to 45ºC.

I asked about whether it was a good idea to turn the unit off on really cold nights, as in Melbourne on the few nights it gets down to around 1ºC or thereabouts? The answer was a definite no, the pipes in the compressor may freeze and then they may burst; it may be a quite expensive way to save a dollar or two. The same applies for when one goes away on a holiday in winter; leave the HWS on.

The stainless steel tank is made by Aquamax in Melbourne, so I'm quite sure that should be good going by how our current Aquamax HWS has lasted.

I was worried about the costs of things that may go kaput, as in the motherboard; which in the earlier models seemed to be a disaster in some places. The official version (I contacted Sanden) is that power surges were the main culprit. Thinking about this and how some of our electronic stuff on high end Laser machines that we had in an industrial situation needed to be protected from power surges, as well as brownouts I would think that their explanation is probably honest.

As our house runs through batteries, via our big Victron inverters, all power to the house is pretty much within 1 volt of 230V AC. Unless I'm reading the stats from Victron with regard to our power generation from the rooftop. I went through the records for the last Jan, Feb, Mar, Apr and not once did the voltage deviate by more than a ripple on the lines and when you check the ripple the deviation is miniscule. Same goes for the frequency, just either side of 50Hz. Unless I'm reading things incorrectly, I think we should not have any power supply issues.

I've found out that the working temperature of the compressor is 63ºC, there may be a bit of an overrun, I don't know.

The tank has a full labour and replacement warranty for 10 years, from then on there is a sliding scale up to 15 years of the cost of the tank and labour would be at our cost. 11 years 20%, 12 Years 40%, and so on at 20% jumps until 15 years where we cover 100%.

Cost of a compressor unit is around $2,500 but that was a bit rubbery and off the top of their technical persons head. The motherboard is around $700.

Compressor is 6 years warranty, full parts and labour.

If anyone has anything to add, I would be very grateful.

Mick.

[yvan]

Optimark, thanks for all this information! I would have been a tad hesitant had I sread it when we were in the process of selecting an electric HWS

Our Sanden was installed in 2013 so it would be a G2 or G3 variant. I haste to report that we have experienced none of the potential issues mentioned, except for the system switching off because of sludge in the water. As I mentioned in an earlier post, the old pipe of our water main seems to be the culprit and I now flush the system every 6 months or so. The process is well documented in the literature supplied and it would take me roughly 15 mins to do so.

We won't complain: at a running cost of $30-$35 per quarter, excluding the unavoidable daily supply charge, we think it is pretty cheap!!!

Cheers,
Yvan

[Beardy]

To me you are investing a lot of money to potentially save a bit of money. If you have natural gas already on I would be looking at a gas storage unit. Purchase price is well under a thousand dollars and there is no fancy electronics and compressors to worry about with potential maintenance dollars or go instantaneous but I find the initial lag a bit annoying.
You have to save a lot of dollars in day to day running costs to recover the additional outlay of the heat pumps

[Optimark]

To me you are investing a lot of money to potentially save a bit of money. If you have natural gas already on I would be looking at a gas storage unit. Purchase price is well under a thousand dollars and there is no fancy electronics and compressors to worry about with potential maintenance dollars or go instantaneous but I find the initial lag a bit annoying.
You have to save a lot of dollars in day to day running costs to recover the additional outlay of the heat pumps

What you say is very true, but it isn't always about saving money; sometimes.

I have looked into the costing for a replacement like for like HWS which is remarkably enough, identical to what we currently have. Apart from upgrades of equipment in the gas supply and burning furnace attached to the unit itself. Realistically we would be looking around the $2,500 mark for a proper like for like changeover. We could go quite cheap by comparison and have something else, but not only is the warranty so low it is under the house stumps low; it sucks gas like a 70's Phase III GT Falcon.

On demand systems invariably use far more water, whether they be electric or gas; I've lived with both last century. Their power usage is also quite high, whether they be gas or electricity.

At the moment, renewable energy usage is rising and it appears most technology is working towards this type of energy consumption. We have rooftop PV generation and battery storage and the expectations of both have been surprising and well in excess of what we anticipated. These expectations have been helped by ensuring all appliances are as efficient as possible in both their energy consumption and water requirements.

The game changer for us, was adding batteries to the house; phenomenal difference. Yes, batteries are expensive and not really going to have a payback until around 9 years and a few months. That was our prediction, yet we went ahead basically on the premise that we cannot take it with us and we may see less interruptions in our power supply. Well the power interruptions we have had last year and this year have been happening, mostly we find out the grid has gone down when the neighbours knock on the door wondering if we still have power. the longest outage was for half a day last year when an automobile hit a power pole not far from us. We also were insulated from the rolling blackout when the bushfires were raging. So from just those points it has been fabulous. But wait there is more, power stability in our house is now top notch.

Our power charges are also going up, similar to what is in an earlier posting in this thread. Predictions have been fed into our spreadsheet with these latest price rises and we think the battery payback will be approximately 6 weeks earlier. Not much, but as each incremental price rise happens, the payback gets closer.

With our house now pretty much running from our rooftop, as far as electrical energy is concerned and evenings are for the majority of the year covered by our batteries, we were looking good. Then we had two people move out in July of this year, which has made a tremendous difference. Young people seem to eat energy, whether that be hot water (don't ask) heating their part of the house or the non stop powering of their electrical equipment as they were working from home since early 2020. Attached is a whole of year power consumption chart for 2020 and 2021 up until today. I took this screenshot this morning.

Remember 2020 was a year where the entire house was permanently occupied 24/7 with usage of up to 4 computers running for a large part of the day, not to mention cooking in the oven, coffee machine, microwave and the myriad of other appliances, including my 2.3kW wood turning lathe. The telling statement is from the screen shot, where it states a meaningful comparison cannot be done as in 2020, we essentially didn't consume power as our net consumption was almost zero. This was from a house where the people didn't leave for weeks on end, apart from trips for food.

Note the drop in power usage for July 2021, this is when two youngies left, well they are both just under 30 so they are youngies. Then look at August this year with just the two of us, it's dropped through the floor. Why not use this now quite surplus power, for other things, rather than give it away for virtually nothing? I have no gripe with the power feed in tariff dropping like a lead balloon, it was always going to happen. We are now at the change of power distribution in our section of the world and whether we like it or not, there are going to be costs; this is one of them.

Some more food for thought!

Mick.

Heat_Pump_HWS_003.jpg

[justonething]

What you say is very true, but it isn't always about saving money; sometimes.

I have looked into the costing for a replacement like for like HWS, which is remarkably enough, identical to what we currently have. Apart from upgrades of equipment in the gas supply and burning furnace attached to the unit itself. Realistically we would be looking around the $2,500 mark for a proper like for like changeover. We could go quite cheap by comparison and have something else, but not only is the warranty so low it is under the house stumps low; it sucks gas like a 70's Phase III GT Falcon.

Hi Nick, I bought the same aquamax as you in 1995. It's not quite as old, but it's getting close. Perhaps 10 years or so ago, there was a time when once's the pilot was blown, it was almost impossible to light the pilot, and I had used the same method as your plumber, and later it deteriorated to the point that it was impossible to light the pilot. All the plumber suggested was to replace the hot water cylinder. They don't fix anything nowadays.
Being bloody-minded, and with the belief that I should be able to fix this because I was once an engineer. I stripped down the cylinders, took the burners out and disconnect all the pipes and found that the cylinder itself was in excellent state, zero rust - that's the beauty of 316 stainless steel. There are a lot of stainless steel around but 316 is as good as you're going to get. It turned out the problem is the thermostat/gas control. A faulty thermostat/gas control will suppress you in lighting it. It's easy to replace, I think the parts cost 100 bux or something. Now you can buy that online. You should get a gas fitter to fit that though.

I haven't had any trouble since... touch wood.

Its just an option for you. I think the cylinder is so well made that it will outlast me.

[Optimark]

Well it is almost six months since this was last visited; we now have a Sanden HWS.

The decision to replace our existing HWS with a Sanden unit, was taken last September; but only when the current HWS either failed or started to fail. This happened in early December with the outer elements of the Aquamax system literally falling apart from corrosion, not the actual stainless steel cylinder, but pretty much everything else.

The Sanden system has been better than expected with regard to supply of HW and the minimalistic amount of electrical energy required to get the water hot. Yes it is summer time, yes we are a two person household and the unit is new, so should be operating at peak efficiency. That said, it is quieter than I remembered when I stood alongside one working in a nearby suburb; whisper quiet comes to mind.

The unit is consuming approximately 890W to 920W when running, with the runtime in this warm weather being approximately 45-48 minutes per day. I fully expect this to be multiplied by 1.5 to 2 times for winter, with the possibility of the compressor switching on some days twice daily. Not 100% sure about that, but I think our usage patterns and long periods of cool weather may dictate something like that.

My consumption figures are approximate as I know in general what the house consumes and when the HWS kicks in the approximate jump is close to 900W of electrical draw change on our constant house consumption readout. There are no fuel costs as the fuel is the atmosphere, just the electrical draw to run the compressor. Within reason and excluding unit purchase costs, our hot water is now basically free until the system karks it.

Mick.