Hi @heacol and welcome to the forum.  I'm sure your knowledge and experience will be much appreciated so please feel free to contribute.   

@derek-m, you are incorrect about oversizing units, most units are inverter and modulate their output, their most efficient point is at approximately 60% of full load, for best performance and running costs, this is where you should run it for the majority of the heating season.

@ceebee, I know this sounds against all common sense, but I can assure you it works, turn all your radiators in your common areas up full, and only turn down your bedroom trv's, move your Valiant controller to a common, central area of your house, remove all other thermostats and timers. Then get hold of Valiant, ask them to send you an engineer to re-program your system and make the controller act as the internal thermostat, it will be free of charge, and they are excellent. The Valiant controller is good, but very complicated. Get the engineer to set it and leave it alone, never touch it again, it will control the temperature in the house to the desired level and will allow your system to operate at the lowest possible flow temperatures which will result in a comfortable environment at a reasonable cost.

Hi Heacol,

It all depends how you specify what oversized actually means. Being an Engineer myself, when specifying systems and equipment I would be looking for normal operation to be at 60% to 70% of full load capacity.

I am not certain if it is still the case, but I do believe that cars were designed for maximum efficiency at 56 m.p.h., but that one with only a 1 Litre engine could still achieve the maximum legal speed limit of 70 m.p.h. Having a 2 Litre engine would still meet the above requirements, but would probably use slightly more fuel.

Therefore I would still expect an oversized ASHP will probably use slightly more electrical energy, than one that it sized to meet all expected operating conditions. The problem with specifying the required size of an ASHP accurately, is the difficulty in fully assessing all the conditions under which an ASHP system may be expected to operate.

The major drawback with ASHP's is that they become less efficient as the ambient air temperature falls, which of course becomes a problem when extreme weather conditions occur.

Hi,

We’re based in Edinburgh and have just had an ecodan installed this month as part of the electrification of heat demonstration project. The installer showed us how to set schedules for the heating and hot water (though not for the legionella cycle) and mentioned that heat pumps are more efficient when the house isn’t allowed to get too cold. The internet seems split between ‘just set it and leave it’ and ‘don’t pay for / use energy you don’t need’, so I’ve joined here to ask your advice. We’re on the octopus go tariff now (after an expensive few days on octopus agile) so keen to make best use of the off peak period from 12:30-4:30 if possible.

thanks in advance for any tips you may have. 

@hjbhome Hi,

Welcome to the forum.

Heat pumps are more efficient when they are heating the water in the central heating system at a lower temperature, details of which you will find in the various posts under Measuring your COP.

They are also more efficient when the outside air temperature is higher.

To get the best performance from a heat pump, weather compensation needs to be enabled on the controller, which automatically adjusts the temperature of the water leaving the heat pump to the lowest value to meet the heat demand.

If you need any further information please ask.

@HJBhome, it depends on your usage/habits.  We lower the temp during the day and at night and raise it in the morning and evening.  But only by 3 or 4 degrees so the house never gets cold.  If your house is extremely well insulated and draught proofed you could leave it the same temp constantly.  As you say there is no definitive guidance on this but it just feels wrong to heat your house when you're not there. It also depends on your radiators; if you have gas/oil heating-sized rads, they will take longer to heat the house than if you have purpose-sized ASHP ones. Did your installer do a room by room heat loss calculation and check the radiator outputs?

We have an Ecodan too and as @derek-m suggests, ours is set on weather compensation.  It's quite noticeable; when the heating comes on now (i.e. in September) the radiators are just warm; when it's colder outside they are much hotter. The installer should have left your legionella cycle set up to run every now and then (two weekly?)

Because Octopus Go is so cheap off-peak it would be worth timing your hot water to heat during that time. And your heating too when it gets colder.  Your ASHP will be less efficient at night because it's colder but this will be offset by the cheaper rate.  

Hi, all.

I'm a newbie. Last few years, I have developed DIY heat pumps and created a DIY heat pump controller. I will post my research results here. Hope it will be helpful to someone.

@gonzho, welcome to the forums and look forward to seeing your results. Please also DM me if you'd like to write an article on this that we could publish on the main site.

@gonzho I will be very interested in seeing what you are doing. We are in the process of building a new controller that will run the system without intervention from the user and produce the best possible performance based on the system it is attached to.

@editor,

Thank you!

@heacol 

Here is a topic with a short description https://renewableheatinghub.co.uk/forums/postid/2006 . The main repository (source code, gerber, etc., and a lot of text) is on GitHub.

And the development process of the controller itself is currently completed.

@gonzho 

Please can you re-post the link, it is not working.