ASHP system fitting additional gas boiler

[tegwin]

I have a bit of a conundrum and would welcome your thoughts.

House currently has a 8Kw air source heat pump (ASHP) and a 10Kw electric heater in series with it.

ASHP works perfectly in the summer to heat the water and warm the house. When the temp drops below a preset level the 10KW boost heater kicks in as well. This works to a point but the colder it gets outside the less heat the ASHP can produce. This means that for parts of the year the house is unacceptably cold.

The heat used to be supplemented by a coal fire but the owner of the house can no longer lift the coal.

The aim is to do away with the 10KW boost heater and fit in a gas boiler so that for the coldest parts of the year the ASHP can be switched off. The ideal situation would be for the ASHP to do most of the work in the moderate parts of the year with some help from the gas boiler to keep things topped up.

I appreciate the ideal situation would be to fit a large thermal store and feed the ASHP and gas boiler into that however the cost of doing that is rather higher than we would like.

Does anyone have any ideas of how an ASHP and a gas boiler could be combined to work together throughout the year?

House is a rather sprawling bungalow with a heatloss of around 24Kw (Depending on how you calculate it) and 17 radiators of varying size.

Current system is a Y plan with 200 litre vented hot water tank.

A complex question but I would very much appreciate your comments.

 

[Tipper]

Have a look at Heating Innovations Limited website, it could offer the answer.
http://www.h2panel.co.uk/

I am wanting to do the same thing but in reverse, ie add an ASHP to my existing Gas boiler heated UFH system to take on the spring and autumn shoulder heating curve and running with the gas boiler in the winter as required. Could add a weather compensator too perhaps.

The H7 panel may do it.

Note: I have no knowledge or experience of how good or bad these systems are, just found it on the web!


The other things to look at are the details of hybrid systems now being offered by the likes of Vaillant, etc, which have far more comprehensive/complex control systems.

What temperature are you running the ASHP on a radiator system?

 

[tegwin]

Thanks tipper, thats exactly the sort of thing I was thinking of doing but wasn't sure if it has been done before!! I wonder how well it works in practice.... If it is just using mechanical type thermocouples there could be a fair bit of hysteresis bounce on the switchover. I might have to give the chap a call and see what he suggests.

I can't remember what the output temp is set to but the typical return temps are around 45-50 degrees. It works admirably for 60% of the year, pretty well with boost heater for 25% of the year but terribly for 15% of the year when its just too cold outside for the ASHP to be viable.
I had looked at the valiant combined ASHP/gas system, the one I saw had the heat exchanged for the ASHP actually contained within the gas boiler making it all very well integrated. I don't have that luxury

 

[Agile]

So much for all those who say that an ASHP can work effectively all year round!

But you don't seem to have considered the obvious!

Firstly, unless its a B&B then I cannot imagine you need all the rooms heated all year round. So my suggestion would just be to close the rads in the unoccupied rooms during the coldest part of the year.

Secondly, if you must have most rooms heated then just buy a few cheap fan heaters and use them during the coldest 15% of the year. That's by far the cheapest solution.

The traditional way to mix ASHP and gas heating is with a thermal store as its so simple to operate and control. There are many other ways to use valves to mix and/or changeover from gas to ASHP.

 

[ajstoneservices]

Why would you need a thermal store or a mixing system of any sort?

What make/model of ashp do you have? Have you read the installation instructions as they may show you how to alter the system so that it will run as an hybrid. When run as a hybrid the ashp will shut down and the gas boiler will kick in................with a couple of valves at most.