Hot water cost double NZ average even with solar

Forums › Home Workshop DIY › Hot water cost double NZ average even with solar

alaw005

37 posts

Geek

#312258 1-Apr-2024 10:08

Hi all

Any advice appreciated. We are a family of 3 and apparently our power usage is twice NZ average. Over last 11 months we average around 20 kwh per day for hot water and the same again for everything else.

I am surprised as we have a Rheem loline solar hot water system. While the system was installed 20 years ago I still would have thought it should save us something not cost more than average. But maybe it's the setup we have? I have sketched our system below, we are two story house with ground floor tank fed by solar and electric element, feeding into upstairs storage tank that has no heater and feeds to house supply with loop back to primary. There is a frequent discharge on roof of steam and water on sunny days.

Nevertheless, I have been looking to replace our system as both tanks over 20 years old and on borrowed time. I was going to replace the solar altogether with heat pump hot water. I am looking at Calitec system which seems ideal and is NZ company. But I am now thinking how about both as per image below. This will replace both cylinders with one upstairs and outside heat pump unit about 10m away on ground. I would then also add the existing solar as direct feed but not sure if I am doing this correct.

I would appreciate any advice on a) why our current system is not appearing to perform, and b) any suggestions for proposed system.

1 | 2

3241 posts

Uber Geek

Trusted

#3212740 1-Apr-2024 10:29

Do you have a smart meter?

Maybe show some examples of your daily power usage to help/

But yes, this sounds like something is wrong if you're using 40Kwh a day!

Do you have a massive home lab with enterprise grade gear?

CPU: AMD 5900x | RAM: GSKILL Trident Z Neo RGB F4-3600C16D-32GTZNC-32-GB | MB: Asus X570-E | GFX: EVGA FTW3 Ultra RTX 3080Ti| Monitor: LG 27GL850-B 2560x1440

Quic: https://account.quic.nz/refer/473833 R473833EQKIBX

tweake

2393 posts

Uber Geek

#3212745 1-Apr-2024 10:48

your existing setup looks really weird. is that correct? is those triple triangle bits valves or just connections? you should have a mixing valve at the top of the top tank and the pipe going from cold to the top of the top tank should be a cold line. it looks like the circ pump pumps circulates through the solar but not the tanks. that would make the solar do nothing at all except boil the small amount of water in the system on sunny days.

one thing to remember with the new tanks the solar/heatpump connections are often coils inside the tank. each coil needs its own top up and pressure relief.

alaw005

37 posts

Geek

#3212749 1-Apr-2024 10:57

mentalinc:

Do you have a smart meter?

Maybe show some examples of your daily power usage to help/

Yes, I might have daily consumption somewhere (will look), in meantime I worked out the following from monthly bills.

Do you have a massive home lab with enterprise grade gear?

No, although have one PC on all time mainly as file server and running proxmox/containers. My son games a lot.

alaw005

37 posts

Geek

#3212751 1-Apr-2024 11:20

tweake:

your existing setup looks really weird. is that correct? is those triple triangle bits valves or just connections? you should have a mixing valve at the top of the top tank and the pipe going from cold to the top of the top tank should be a cold line..

I thought this was weird setup, although maybe the values are special types? Particularly the 4-way value in the middle and maybe the 3-way value is a diverter based on temperature difference? I really don't know about plumbing so these are guesses. The following is photo of actual values on bottom tank.

The following is top tank.

tweake:

...it looks like the circ pump pumps circulates through the solar but not the tanks. that would make the solar do nothing at all except boil the small amount of water in the system on sunny days.

That would explain that whenever the sun is out steam and hotwater streaming down roof. That might mean electric element working extra hard. I did also wonder if electric element should be in top cylinder rather than bottom.

alaw005

37 posts

Geek

#3212816 1-Apr-2024 12:23

Just a thought ... is it possible the 4-way value works along the lines of the following?

tweake

2393 posts

Uber Geek

#3212826 1-Apr-2024 12:42

alaw005:

Just a thought ... is it possible the 4-way value works along the lines of the following?

same problem. hot water from the solar gets sucked straight out of the tank and back to the solar. you cannot have the in and out at the same location on the tank, its not going to work. if they had joined the pipe going out of the top tank to the solar, ie disconnected both off the bottom tank and connected the ends together, then the pump would pump the solar through the tanks and it would work.

i also wonder about the pipe that goes from the top of the top tank to the cold in on the bottom tank. does that have a non-return valve on it?

some better pics of the pipes would be good.

tweake

2393 posts

Uber Geek

#3212830 1-Apr-2024 13:00

alaw005:

Just a thought ... is it possible the 4-way value works along the lines of the following?

i think thats meant to be called a "solar 5 way valve". its meant to have an extension on it so the hot water is fed into the center of the tank, to avoid the hot water being sucked back out.

i'm not sure why they would bother seeing there is a pipe from the top of the tank which makes it easy to circulate through the whole tank.

alaw005

37 posts

Geek

#3212836 1-Apr-2024 13:44

Thank you, this confirms for me that the current setup is not correct. But if configured correctly the solar is probably worth keeping. Unfortunately, I can't really test anything without going all in as the bottom tank is 40 years old and plumber won't touch the valves without doing tank replacement. We had a leak a couple of months ago and he said we are on borrowed time.

Any thoughts on the Calitec option? I'm not sure I've shown solar correctly, should this draw from second cold in and feed into the second hot out, noting these are in referse from what should be. Calitec have a wet back option would that be better but if solar is closed loop how do I ensure has water in it.

tweake

2393 posts

Uber Geek

#3212841 1-Apr-2024 14:11

the calitec looks like an interesting system. i have no idea on the brand.

its a gas to the cyl setup (instead of taking water pipes out to the outside unit) which is better in cold areas (no outdoor pipes to freeze). but it does mean the tank must match the outdoor unit as the coil in the tank is the indoor part of a heat pump. the water pipes to the outside type can work on any hot water tank.

its R32 so water temps a little lower and performance drops off a fair bit with lower outdoor temps compared to co2 models. where you live will make a difference in how it runs. its far more suited to auckland than chch. tho would great with a wetback.

i think it may be PV ready, so replace the water panels with PV panels.

mentalinc

3241 posts

Uber Geek

Trusted

#3212845 1-Apr-2024 14:16

The thinking re the daily level if you can see it, you might see some spikes in the usage which you can then work out what may be causing it.

But seems others are suggesting the plumbing hasn't been set up suitably so not working properly so you're heating 600L of water all the time with electricity which would very much explain power usage

CPU: AMD 5900x | RAM: GSKILL Trident Z Neo RGB F4-3600C16D-32GTZNC-32-GB | MB: Asus X570-E | GFX: EVGA FTW3 Ultra RTX 3080Ti| Monitor: LG 27GL850-B 2560x1440

Quic: https://account.quic.nz/refer/473833 R473833EQKIBX

tweake

2393 posts

Uber Geek

#3212848 1-Apr-2024 14:35

i think also the cold temp sensor is on the wrong side. ie its on the water inlet instead the outlet (to the solar). if the controller is looking for a difference in temp, it won't read that the tank is up to temp and will keep pumping hot water around longer than it should. also whenever the water is used, the cold incoming water will turn on the pump (because it makes a big difference in temp between the solar and the cold water , even tho the solar could be colder than the tank. thus the solar is getting rid of the heat at certain times.

i assume the top tank is in the ceiling, its generally better if the tank is inside the house. that way you loose the heat to the house rather than outside. so if you replace it, keep the tank downstairs if at all possible.

eonsim

398 posts

Ultimate Geek

Trusted

#3212873 1-Apr-2024 14:46

Worth checking the overflow outlet, friends had a massive hot water bill then found out the hotwater tank and constantly been leaking out the overflow outlet and the cylinder needed replacing.

As others have suggested, it may be simpler to rip out the solar hotwater system and multiple water cylinders and replace them with a small photovoltaic solar install and heatpump hotwater system. Doesn't take much PV to heat water and any spare power can be used to reduce your power bill.

alaw005

37 posts

Geek

#3212874 1-Apr-2024 14:47

I think the sensor on inlet as picking up hot return from top tank. I suspect the return is loosing a lot of heat and not needed in which case sensor on solar side. I was going to keep top tank in attic as closer to outlet to rest of house and more room as is walk in attic. Also frees up space downstairs for future bathroom renovation. We in Kapiti area so doesn't get too cold.

tweake

2393 posts

Uber Geek

#3212880 1-Apr-2024 14:57

eonsim:

Worth checking the overflow outlet, friends had a massive hot water bill then found out the hotwater tank and constantly been leaking out the overflow outlet and the cylinder needed replacing.

doh, i completely overlooked that.

as the system is boiling and releasing pressure, its drawing in cold water which is being heated by the element not the solar.

tweake

2393 posts

Uber Geek

#3212884 1-Apr-2024 15:03

alaw005: I think the sensor on inlet as picking up hot return from top tank.

it may be meant to, but without a pump to circulate there is no flow through that pipe, so it would never work. assuming your diagram is correct, and it should have a one way valve on it somewhere, and it doesn't go up to the tempering valve, it otherwise does absolutely nothing.

1 | 2