New System thoughts.. Got Oil, would like Air Source as well

[jammers]

Hi All,
I was just going to have my boiler (its a worcester danesmoor 15/19) replaced with a new efficient oil boiler (worcester xx).
However because if the ever increasing cost of Oil, I thought I would research Air Source.
My system runs off the worcester and I have a cylinder upstairs which is vented into the cold water tank in the roof. About 3 years ago an extra 2 pumps were added to the system (one for HW and one for CH) to cope with the extra radiators and hot water demand.

My questions are;
1. To heat the hot water from the air source i could just connect it up to another take off on the existing cylinder? But how do I connect it to the CH? I have been told an accumulator could do both? what are your thoughts on this and what accumulator's could I look at? Also what alternatives do I have?
2. How far away from the Air Source pump can the boiler and cylinder be?
3. Do I need any other equipment to control this hybrid system?

Sorry for all the questions, would like to just get it clear in my mind so I can effectively out it together.

Cheers
James [/b]

 

[stem]

I have maintainance responsibilities for air source heat pumps and boilers, but have no direct knowledge of a combined system, however some of the information I have discovered may be of help to you. There may be new technologies available, that others can perhaps advise you about.

Air source heat pumps are not capable of producing the high temperatures that are achieved by boilers. Therefore they are not able to heat traditional radiators to a high enough temperature to warm your home in the same way that your boiler does. As the return water temperature from the radiators would probably still be higher than the starting temperature produced by the heat pump I don't believe it would be able to add any heat to the process.

For this reason, heat pumps are generally used for 'air to air' heating, which also allows them to be operated in reverse and provide summer cooling.

Air source heat pumps can be used in an extremely well insulated building with wet underfloor heating systems which operate in the region of 40 degrees C as they have a much larger surface area to emit sufficient heat to warm the building at the lower temperature. However, one of the problems with air source heat pumps, is because they collect heat from the outside air, their output falls off as it gets colder outside, just when you need it most.

Ground source heat pumps are less prone to the 'drop off' as the ground retains heat better than the air.

Heat pumps can be used to warm stored domestic hot water supplies.

 

[simond]

Assuming you have radiators, an ASHP will offer minimal, if any, savings over a modern condensing oil boiler.

Certain types of heat pump can work with a boiler 'docked' to the unit. This is designed to run the heat pump in most cases except where outdoor temps are low.

However, the catch is that to obtain FiT you have to comply with the latest MCS requirements re radiator sizing. In most cases you will end up with rads 300% greater output than you have now. And there are other requirements too.

All my customers, when looking at the cost of a bivalent system (this is the term to describe your proposed system) have decided not to bother. Oil is king unless you happen to live in a modern, fabulously insulated airtight house with underfllor heating.

If yiu Google 'Sutherland tables' you will see some excerpts from their real life research on heating costs. They are impartial, but in this month's OFTEC Installer magazine it showed that an ASHP would in nearly all cases work out slightly more expensive to run than oil.

If you get an oiler fitted this month by a Worcester Gold level installer you will not only have a higher efficiency boiler but also a 7 year parts and labour cover free.

 

[DeltaT2]

There's some merit in adding an ASHP for Spring/Autum heating. But as said, not realy worth it. Water Source Geothermal would be much better, if you're near a river or large Lake/Loch.

Another cheap install/cheap running cost option is a cheap Chinky split air to air invertor unit.

We've one customer that's got 3 air to air split unit on cheap leccy tariff and they're delighted with. But air heating is cr.p.

 

[dcawkwell]

Air source heat pumps work fine in conjunction with an oil or gas/lpg boiler.
The oil / gas boiler comes on to give a boost when necessary.
I suggest you keep your old oil boiler and got for this configuration.

The air source heat pump and oil/gas boiler work in what is known
as a boiler cascade.
I would suggest the use of a low loss header/buffer tank to connect
the two heat sources together.

Better still leave the UK to climates warmer where spending all your money on fuel and taxes isn't required. That is my plan.

 

[simond]

Your above post suggests a lack of understanding of both the technical and legislative issues when you couple a HP and Fossil fuel boiler.