SunAmps to replace hungry water cylinders?

[KatyJ]

Hello. My first post, thank you for taking the time to read. I'd appreciate any comments / advice, particularly from those with experience of sunamps

 

North West Scotland

3 x Self Caterings. One bed, one living / kitchen (elec oven, microwave, fridge freezer), one bathroom with shower and bath. Approx 50m2

2 x elec radiators and 1 towel rail per unit 

1 x wood burning stove per unit

1 x 210L megaflow per unit (2 x 3kW switches each)

 

Elec units per year 20,000 including other buildings / laundry etc.

 

I'd like to drive down our usage considerably and take less from the grid. Have already placed all electric radiators on WiFi switch. Guests can boost for an hour using a button to supplement the wood burner but can no longer put heating on permanently and go out for the day leaving the windows wide open;)

 

Exploring 3 x Sunamps with 1.2kW (?) panels to each Unit to trickle charge through the day, with the hope that, in my inexperienced mind whilst trying my best to educate myself, the following can be achieved;

 

1. During our busiest months, our long daylight hours, the solar will contribute a high percentage / all of the hot water demands
2. We won't be needlessly boiling a 210L tank twice a day regardless of how much / little our guests use. Some don't take a bath everyday, some not at all, some morning and night (!!!!) It's part of what we sell, they can relax in the bath with a stunning view, protected from the outdoor climate
3. The losses are less so we will straight away save elec units per day this way
4. The Sunamp only converts power to hot water on demand. So if someone washes the dishes, has a shower etc, the entire 210L doesn't then have to be boiled back  up to temperature when the timer comes on for 2-3 hours twice a day?
5. I now believe 210L is a lot of hot water even for a bath and a shower or two, if just two people? Two baths? So we hopefully will no longer be converting that amount of energy to water when it's not required. I read that a bath is just 80L of water - is that right I find it hard to imagine though understand mixed with cold water
6. We can set the Sunamp on a timer to charge from the grid / not drop below a certain charge so guests won't be disappointed if no hot water? This is a bit I'm yet to understand. We could leave a boost button that if their water runs out at night and they know they will need a shower first thing in the morning that the water will be hot again for them?
7. Not got a meter - don't ask. One day, hopefully. Not guaranteed the night time useage will be around for ever so I'm not banking on this at the moment regardless. Priority is get the units we seem to burning through lowered as much as possible.
8. Is it possible to install solar panels direct to SunAmp and off line / off grid from the on grid system? The panels aren't the most expensive part of the package, so if we added more panels it wouldn't impact any G98/G99 etc?
9. Is 1.2kW solar trickle charging during summer months going to help general usage or do realistically need more? 
10. I realise could put solar panel to charge our current cylinders. I believe we would need at least 3.6kW array per cylinder to get sufficient charge though as it's not best suited to trickle charging, the SunAmp can use every bit of charge from the panels though, regardless how small W per hour. Changing to Solar thermal / heat pumps (please don't talk to me about heat pumps) will require a new tank regardless. So offset that cost against the SunAmp?
11. Legionella - it won't be such a concern for us and our risk assessments / management water under the 60 degrees is no longer stored in a tank

 

If anyone is willing to pick the above apart (I'd appreciate kindness at the same time - I fully admit I'm a learner!) I'd be extremely grateful for any advice, thoughts.

 

Thank you,

Katy

 

 

 

 

[Conor]

Sunamp is a heat battery, based on phase change material, but it's still essentially a large mass that is heated by electric wires.

 

You can just use a solar diverter on your existing tanks - assuming that the immersion element is at the bottom of the cylinder. You don't need 3.6pkW, likes of an Eddi diverter can work with a couple hundred Watts. Resistive heating is resistive heating, no matter what the packaging or sales pitch is.

For heating when not sunny, you can time the tank to be heated on off-peak electric.

Will be less efficient (higher standing loses) than a sunamp, but how long would it take to make up the difference based on the cost of three sunamps?!

[SteamyTea]

Be helpful if you had some time of use data, then you can see if just changing to a more suitable ToU tariff can make you savings.

A Sunamp is an expensive way to store hot water.

If you must go down a technology route, how about preheating DHW with a heat pump. Get the incoming mains temperature up to 35⁰C in say a 1000 litre cylinder, then boost up to say 48⁰C with either an immersion heater in a secondary 50 litre cylinder on site, or an instantaneous inline heater.

Any PV can heat either the large cylinder and/or the smaller ones.

 

As you are supplying hot water as a service i.e. as part of the holiday experience, you don't want to run out, so you have to build in redundancy, Sunamps are not that unreliable, just tricky to fix. 

 

[Iceverge]

Vailant Arostor ESHP or similar would cut the DHW electric to about 40% of your current amount. Installed cost about £2.5k

 

https://professional.vaillant.co.uk/for-installers/products/arostor-domestic-hot-water-heat-pump-58880.html

 

An A2A heat pump would provide heat at 1/4 of the cost of a resistance heater. Installed cost about £1.5k

 

https://www.saturnsales.co.uk/Daikin-FTXM25R-Wall-Mounted-Heat-Pump-Air-Conditioning.html

 

Solar PV and a diverted will roughly provide all the DHW needed from April to September at a rate of 1kWp of panels per person. Cost about £1k per installed kWp. 

 

 

[ProDave]

Hot water for guests is harder than hot water for your own house.  You have no control and no idea how many times they will shower and at what time, so you need hot water available all the time.

 

There is a good argument for electric heated showers.  Then you are only heating the water they use for showering nothing more nothing less no waste.  Then just heat the top half of the megaflow cylinders with the top immersion heater for basin and sink hot water.  Solar PV with a diverter to help with that.

 

I am well aware if the don't give a **** attitude of guests having previously run a b&b and found the room thermostst up at 30 degrees and the window wide open.

[Dillsue]

I've little knowledge of sunamps other than they come up on here regularly with problems. I wouldnt use a sunamp on a rental property unless I had a back up for hot water. Anything you put in needs to be repairable by yourself or your average local plumber so it can be repaired ASAP when you've got guests

 

For the heating, leave the towel rail in the bathroom controllable by guests but switch the rest of the heating with a movement sensor so the heating goes off 1/2 to 1 hour after last movement is detected. Or, you could put switches on the windows to inhibit the heating if they're left open. Add a timed inhibit and the heating can be off during the day and come on late afternoon if the windows are closed. That would keep the accommodation cosy for returning guests without it all going out of the windows

[sharpener]

On 22/02/2024 at 15:08, Dillsue said:

I've little knowledge of sunamps other than they come up on here regularly with problems.

 

Flamco also make phase-change thermal stores. At first sight there are some similarities to the Sunamp e.g. the diagonal arrangement of the four pipe connections. No idea about price or availability in the UK.

[JohnMo]

1 hour ago, sharpener said:

Flamco

£5k for the small one, that's a cylinder and 5 years heating on direct electric at 7kWh day.

[sharpener]

Thanks. And that is for 3.5kWh. A 260l tank from Newark will store 9kWh for me, and even filled with 20% glycol will cost a small fraction of that.

 

As the principle is well established and SA have had the formulation of their 58C phase change material sorted out long since, it is a mystery to me why the engineering of the product seems so poor and there is no effective competition in this marketplace. (The mix of compression, soldered and Speedfit fittings described earlier sounds like a test rig thrown together in a university lab not an engineered product.)

 

The USP seems to be the compact size of the units, but it must be a very small property indeed that has no space for a hw cyl. Even my first flat had an airing cupboard with a Fortic tank in it.

[Mike]

8 hours ago, sharpener said:

As the principle is well established ... it is a mystery to me why ... there is no effective competition in this marketplace.

It seems likely that will change. The EU has been funding a number of demonstration projects to the tune of 7.7 million euro, which will build up expertise in multiple companies. One of their FAQs says we expect to see the first real market applications from 2025 onwards. More at https://www.heat-insyde.eu/

[JohnMo]

25 minutes ago, Mike said:

seems likely that will change.

Why, they are stupid expensive, hot water cylinder isn't. Control is way simpler for the cylinder also. From what you see on here, a cylinder is way more reliable, a thermostat is really all that can go wrong, so easy to fix or replace. Certainly with heat pump storage temperature (50 and below) heat losses are pretty low from a cylinder. And a cylinder can be heated by heat pump easily, phase change not so easy and if you do the CoP is dreadful, because the heat flow has to be above the phase change temperature at all times. Most heat pumps will not do that anyway.

[Mike]

5 minutes ago, JohnMo said:

Why, they are stupid expensive

New technologies are almost always stupidly expensive. Once production ramps up cost falls.

 

The first microwave oven cost $5,000 in 1947 - equivalent to around $70,000 today. Clearly they were never going anywhere...

 

9 minutes ago, JohnMo said:

And a cylinder can be heated by heat pump easily, phase change not so easy and if you do the CoP is dreadful

And the EU project is working on that - combining heat pumps & PV with phase-change storage, to achieve high COPs, for both district heating and individual homes.

[JohnMo]

9 hours ago, Mike said:

, to achieve high COPs

Think that may be stretching. Better CoP possibly but not high CoP. The fundamental issue with phase change is it requires the the heat source to always be above phase change temperature, CoP can never be that good. So if phase change temp is 50 the heat source needs to be over 50 plus the dT, so about 58-60 throughout the heating cycle 

 

Cylinder heating, the heat source only needs to be hotter than the cylinder temperature, so heat temp ramps up slowly with the cylinder temperature, only when the cylinder is at full temp does the heat pump output get in to 58-60 range.

 

So CoP will always be better with a cylinder.

 

PV doesn't need to be integrated, if it's available it is is utilised if the heat pump is running. Just time DHW for the muddle if the day when PV is likely to be available.

 

The heat losses is also a red hearing, most losses come from poorly installed and badly insulated piping on a cylinder or a phase change store for that matter, not the vessel it self. Measuring the shell temp of my C rated cylinder it's 21 degrees (50 degs inside) in a 21 deg room, so heat loss is next to zero. Even if it's loosing heat the MVHR extract captures it and it's distributed around the house.