Best way to heat and store hot water with ASHP and Solar - am I being stupid?
We're about to start renovations and will be installing an ASHP with Solar PV and batteries. For the hot water, I've looked into solar diverters, Mixergy tanks and phase change systems, and no doubt there are other systems to consider.
BUT, aren't all those options irrelevant if you've got an ASHP?
If the ASHP is 300-400% efficient then for every 1KW of input i'll get 3-4KW of output, whereas I believe all the other systems are more like 1KW of input for 1KW for output and so I believe it's as simple as getting the best cylinder I can afford and connecting it only to the ASHP?
Or am I being stupid and missing something or misunderstanding something?
You are correct, ASHP is the most efficient method, solar diverters were popular before batteries became widely available and prior to any heat pump uptake.
Phase change like sunamp is as inefficient as direct heating the only advantage is if you have no space for a cylinder its a smaller unit.
@nickmorgan you are not missing anything at all and when you dial in the import and export rates on electricity tariffs then a diverter is even more uneconomical.
For example Octopus export is 15p per kWh and import on cosy ~13p per kWh and the effective COP for DHW is ~3 so heat DHW in cosy cheap periods and export all excess. Early afternoon is both warmer so higher COP and possibly your PV could be powering the ashp and exporting the rest.
If you have an EV then you might use other tariffs which could work well too.
2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC
@nickmorgan you’re absolutely spot on with your thinking. It took me a while to fully grasp this, but a few years ago, it clicked for me too, and we removed our solar diverter to let the heat pump handle hot water.
The only “quirk” with hot water production is that the heat pump has to work harder to deliver it. For example, we heat our hot water to 45°C, but to achieve that, the heat pump needs to run at a flow temperature of around 55-60°C. This is because you need a higher flow temperature to ensure effective heat transfer through the coil or plate heat exchanger in the cylinder. If you ran it at 45°C, there’d be virtually no heat transfer, and the water wouldn’t get hot enough.
You can see this in action in the attached image. The two spikes correspond to our morning showers and an evening bath.
Buy a copy of the The Ultimate Guide to Heat Pumps
Subscribe and follow our Homeowners’ Q&A heat pump podcast
- 26 Forums
- 2,199 Topics
- 48.4 K Posts
- 36 Online
- 5,854 Members
Join Us!
Podcast Picks
Latest Posts
-
-
RE: Heat Pump Installers: Competence, Illusion and the Hard Truth Homeowners Must Face
@pirate-rich there’s a lot to do and plan, and the wish...
By Mars , 4 hours ago
-
RE: Why Air Release Valves and Deaerators are Non-Negotiable
@chas-b and @pirate-rich spent the day with us today ta...
By Mars , 4 hours ago
-
RE: Help me keep the faith with my air source heat pump installation
@adamk Its a bit complex: My 28mm primaries run for a...
By JamesPa , 5 hours ago
-
Can you separate out the scop data between hot water an...
By Andrew J H , 8 hours ago
-
RE: Solar Power Output – Let’s Compare Generation Figures
Further, these bar charts may throw a few more lumens o...
By Toodles , 9 hours ago
-
RE: Heat pump and wifi kit connection.
Wi-Fi kit covers any Samsung device that has a modem in...
By Alfapat , 1 day ago
-
RE: How to Understand Wiring Up a Heat Pump
I’m watched @pirate-rich rewire our wiring centre last ...
By Mars , 1 day ago
-
RE: Sizing - Save me from my headache
If you get an R290 pump you should be able to heat the ...
By JamesPa , 1 day ago
-
RE: Large heat pump options for church building
@aventus-eco Thanks Sean, will drop you a line.
By Josephiah , 1 day ago
-
RE: Moving FIT array onto a Tesla Powerwall 3 possible?
@toodles that’s good news for @adamk
By Judith , 1 day ago
-
RE: Samsung Gen 6 - Schedules not working
@technogeek That sounds very logical :-). I will give i...
By bontwoody , 1 day ago
-
RE: Who's your electricity provider and what's your tariff?
Considering Octopus states all their electricity is gre...
By AgentGeorge , 1 day ago
-
RE: Heat Pump + Tado Setup: Smarter Control for Secondary Pumps?
@pirate-rich thanks for the reply. If I were to explo...
By Lloydi , 1 day ago
-
RE: Seal the Deal: Don't Let Your Heat Pump Leak Energy
@transparent I think the committee might get into some ...
By Toodles , 1 day ago
-
Samsung ASHP Support in Midlands area?
Hi all, Per title.... can anyone recommend a ASHP ser...
By Andehh , 1 day ago
-
May I present the maths I referred to earlier when disc...
By Transparent , 2 days ago
-
RE: RDSAP10 effect on existing heat pump EPC rating?
How many times and dates have epc sap rules been change...
By Tim441 , 2 days ago
Members Online
No online members at the moment