Domestic Air Source Heat Pump

[borderfox]

Current Scenario

• 4 Bed semi-detached with 100mm cavity insulation, built 2005.

• Approx.140m2
• Double glazed
• Reasonably airtight.
• Wood burning stove in living room (although I don't use it, I put it in for the moment to block up an energy efficient open fireplace)
• Central heating & hot water via oil boiler feeding rads & hw cylinder

I have the opportunity to avail of a £2000 grant to install either an air-air source heat pump or an air-water source heat pump.
The research I have done so far indicates that I have to be very careful about which system I go for due to the running costs. My own circumstances mean that i'm not in a position to invest much extra myself by way of capital costs.
Whether I go air-water or air-air, I want to use the system to supplement my existing oil-based system - using it at the lower electricity tariff times and at the temperature range when the unit has the highest COP. Otherwise, I want the oil boiler to take over.
On this basis, can anyone recommend potential systems that might fit the bill?

[borderfox]

typo should read ..."energy inefficient open fire"....

[freezetech]

you ll find air to water system will be 40% cheaper to run than your oil boiler i think air to air would work out expensive to buy to do that size of house

[borderfox]

you ll find air to water system will be 40% cheaper to run than your oil boiler i think air to air would work out expensive to buy to do that size of house

Thanks freezetech. I would be quite happy to switch permanently to air-water - if it does work out cheaper but the numerous reports of excessive running costs has raised the anxiety levels as regards whether i'm about to make a bad move or not!
There are a couple of factors that might mean I need to mix between oil boiler and heat pump. Firstly, someone suggested to me that my rads might not be fully effective if used with a heatpump. I don't want to replace right now - my logic would be to use heatpump to get them to a certain temp - and then the oil boiler will finish the job.
Secondly, boiler can get cylinder up to temp to tackle any potential legionnaires problem.
Is my thinking rational here??
Also, do you believe air source pumps to be cost effective regardless of ambient external temperature?

Air-water is my preference if its possible to integrate with my existing oil boiler system (oil boiler is external unit just outside back door).
If I was to use air-air, I would just be interested in using it to supplement existing heating - using it when its most efficient to do so - with internal side of it opening into downstairs hallway.

[mad fridgie]

Air to air firstly, if you want to heat a house, then you need multiple heads (like rads) or a ducted system, it all about moving energy.
Air source on your rads, you need to change your thinking on how you operate. There is alot of B******T around heat pumps. They are great and cheap to run "only" if they are applied correctly.
If you want to go the rad way (internal work completed), then a must is to increase the water flow flow through the rads. (if you have micro bore piping to your rads, then this maybe difficult) if you have 1/2" then good.
The object is to have the water running through as cold as possible, You do not run on a timer, you average your load over 24hrs, not over the time period you have on your boiler controller

[borderfox]

Air to air firstly, if you want to heat a house, then you need multiple heads (like rads) or a ducted system, it all about moving energy.

Air to air is very much a last option for me. I would only use it to get some heat into the ground floor using one unit - supplementing existing heating - whilst making full use of the £2k grant.

If you want to go the rad way (internal work completed), then a must is to increase the water flow flow through the rads. (if you have micro bore piping to your rads, then this maybe difficult) if you have 1/2" then good.

I believe its 1/2".
So using existing rads isnt necessarily a problem then?
Any system recommendations?

Thanks for posting!

[mad fridgie]

You allow your heat pump and rads to reach equilbrium (it is energy that you are after) Do not force the heat pump temp up (restricting flow). You leave the heating on 24hrs a day. How you control your temp depends upon your present system. Do you have air thermostaic valves, room stats in each room, a common stat?
You could control your boiler on return temp or outside ambient.
Without much more detail, I really can not help any further

[borderfox]

How you control your temp depends upon your present system. Do you have air thermostatic valves, room stats in each room, a common stat?
You could control your boiler on return temp or outside ambient.

At the moment, I have no stats whatsoever - just a simple analog 'clock' for the oil boiler. Obviously, this is something I plan to rectify. My latest thoughts on this was to use wireless radiator thermostatic valves on all the rads.

[mad fridgie]

That sounds like a good idea, make sure that you do not restrict the flow through the heat pump (best to have 2 pumps and a balancing pipe) your boiler could also be connected to the balancing pipe. (presume boiler has its own pump)

[olddog]

you ll find air to water system will be 40% cheaper to run than your oil boiler i think air to air would work out expensive to buy to do that size of house

Freezetech, Is that based on UK or Eire electricity prices ?

Eire domestic electricity is circa 16c/kWhr. There is a night rate tarriff which is about half this

[VRVIII]

Air to air is very much a last option for me. I would only use it to get some heat into the ground floor using one unit - supplementing existing heating - whilst making full use of the £2k grant.
I believe its 1/2".
So using existing rads isnt necessarily a problem then?
Any system recommendations?

Thanks for posting!

Hi,
I wouldn’t say you will be able to utilise your existing radiators unless you are thinking of a HT (high temp) system. You will probably need to upsize the radiators to obtain the same heating capacity with a low temp system (50 C max flow temp)

You could also consider installing the air source heat pump in a bi-valent configuration with your existing heating system this would allow your boiler assist when required.

[fridge doctor]

Borderfox, I have a reliable contact in Eire. He uses only German engineered equipment. As he is on your doorstep, he might be worth a phone call to assess your needs. I don't think I can advertise on the forum, so you would have to send me a PM if you are interested.

Trevor.

[mad fridgie]

Hi,
I wouldn’t say you will be able to utilise your existing radiators unless you are thinking of a HT (high temp) system. You will probably need to upsize the radiators to obtain the same heating capacity with a low temp system (50 C max flow temp)

You could also consider installing the air source heat pump in a bi-valent configuration with your existing heating system this would allow your boiler assist when required.

When using a heat pump the load is split over a potential 24 hour period, compared to a short period with a boiler (which also has to allow for recovery "energy lost when the boiler is not running.) This change in heating method allows for a much lower rad temperature. Very simplistic example: Rad system 60C water 20Kw runs 10hrs aday, same rad system (same surface area) with heat pump runs 20hrs needs to be 10Kw and water temp 40C (not quite true as heat transfer co-efficient of rads is not linear) Same amount of energy introduced, so house temp is the same
You can not change a heat pump for a boiler, with out a change in water flow rates and control methodology
As stated above and I agree leave the boiler in circuit and use in conjuction at the extreme ambients.

[borderfox]

Freezetech, Is that based on UK or Eire electricity prices ?

Eire domestic electricity is circa 16c/kWhr. There is a night rate tarriff which is about half this

Yes, thats right. And the folks that have got the night rate meters installed reckon that a lot of the saving goes on the 'ground rent' they have to pay for having this metered seperately!

[borderfox]

Borderfox, I have a reliable contact in Eire. He uses only German engineered equipment. As he is on your doorstep, he might be worth a phone call to assess your needs. I don't think I can advertise on the forum, so you would have to send me a PM if you are interested.

Trevor.

Thanks fridge doctor. PM sent.

[borderfox]

(presume boiler has its own pump)

Yes, thats right.

[borderfox]

Thanks fridge doctor. PM sent.

Sorry..don't think pm's are possible right now..?

[freezetech]

don t forget if you control the temperature control with trv s then you ll need to leave one rad without one normally bathroom for the water to go some where

[freezetech]

it don t matter the price on your electric tarriff the saving is on kilowatt hours used

[borderfox]

You could also consider installing the air source heat pump in a bi-valent configuration with your existing heating system this would allow your boiler assist when required.

Yes - this was what I had intended. I understand the point that freezetech made earlier about its natural use being to run at low temp all the time - but given that electricity is so expensive here, maybe this is the most cost effective way to use the system? Is there much extra grief in a bi-valent configuration or is it straightforward and without additional expense?

[borderfox]

don t forget if you control the temperature control with trv s then you ll need to leave one rad without one normally bathroom for the water to go some where

Thanks - I better bear that in mind.

[mad fridgie]

Yes - this was what I had intended. I understand the point that freezetech made earlier about its natural use being to run at low temp all the time - but given that electricity is so expensive here, maybe this is the most cost effective way to use the system? Is there much extra grief in a bi-valent configuration or is it straightforward and without additional expense?

Energy is energy what is bigger 20*2 or 10*4.
If the heat pump is 40% cheaper to run then it is 40% cheaper to run, when we say it runs 24hrs we mean it can run 24hrs, when temps are reached it turns off. When you turn off the boiler the house becomes cooler, when you turn back on you have to reheat the house before your reach a comfort level. This normally means an overshoot due to the thermal mass being colder, with a steady state system you normally find that the desired comfort level setting is somewhat lower than a timed system.

[brunstar]

border fox,
try going to www.uswitch.com and seeif there is a more competative rate for your area, some of the fixed tarrifs are quite good at the moment at 8 to 10p per kwhr..

[brunstar]

normally if you threaten to change energy suppliers, your current supplier will smarten up their act and offer you a lower rate.
depending on how many suppliers of energy you have in your area?

[borderfox]

normally if you threaten to change energy suppliers, your current supplier will smarten up their act and offer you a lower rate.

Thanks brunstar but I'm south of the border. Our system has just been deregulated but nevertheless there are just three suppliers and I already have the cheapest. However, whether its Britain or Ireland, we can only expect electricity prices to rise in the medium term - so its definitely a factor when it comes to systems like these.

@madfridgie: what you say seems to make sense but I guess i'm apprehensive as I have to 1. make sure i have a system that functions and 2. make sure running costs are not exorbitant. What do you think of VRVIII's point about the rads not being able to do the job?
Is there any specific system that anyone here would recommend that I could investigate further?

[paceinternet]

Radiators in the UK are normally specified at delta T 50 deg C. Meaning if the room temperature is expected to achieve 20 deg C, then the water temperature will need to be 70 deg C to dissipate the kw rating.
If your water temperature is 50 deg C, you have a delta T of 30, and that corresponds to an output of about 50% of the rating. So a 3kw output radiator will achieve 1.5 kw. If the heat loss calculation for the room is 3 kw, you will never achieve 20 deg C at the lower water temperatures however long you run them for.
You need more radiator surface area, or underfloor heating or fan convector heaters at lower water temperatures.
Generally, a K2 double radiator with 50 deg C water will give out the same as a K1 single at 70 deg C water.

[mad fridgie]

How many hours a day do you run your boiler on the timer, does the boiler turn off on its internal thermostat (when on with the timer) How big is your boiler.
The daily run time * boiler Kw rating, will give total daily heat loss.
If your run time is over a half a day then a LT heat pump is not suitable, if well below a half a day then is. (average) At extremes lets say 10% of the time you kick your boiler in.
You need to calculate on long term averages, not the extremes. As you already have the boiler the choice is easy.
What has been found out is that most CH installers over size the rads.
Are you comfortable at present, "yes"
What is the ambient temp "coldish"
No check you actual boiler runs hours
(sit and watch it) do not rely on timer run hours.

[brunstar]

Radiators in the UK are normally specified at delta T 50 deg C. Meaning if the room temperature is expected to achieve 20 deg C, then the water temperature will need to be 70 deg C to dissipate the kw rating.
If your water temperature is 50 deg C, you have a delta T of 30, and that corresponds to an output of about 50% of the rating. So a 3kw output radiator will achieve 1.5 kw. If the heat loss calculation for the room is 3 kw, you will never achieve 20 deg C at the lower water temperatures however long you run them for.
You need more radiator surface area, or underfloor heating or fan convector heaters at lower water temperatures.
Generally, a K2 double radiator with 50 deg C water will give out the same as a K1 single at 70 deg C water.

Yes this is the key, the right system for the right application, as stated in the above quote, the rads do have to be sized for the correct flow temperature.
With heat pumps you don't really want to push you flow temp above 45 degrees ideally 40 degrees , if you are going down this route, it would be best to use fan assisted radiators to increase the convection over the radiators.
with low temp, the underfloor route is the best option with greater surface area.

[borderfox]

How many hours a day do you run your boiler on the timer, does the boiler turn off on its internal thermostat (when on with the timer

7 hrs/day - and yes, it turns off on int. 'stat.

How big is your boiler.

26.37kW Firebird 7090 Heatpac

[borderfox]

Yes this is the key, the right system for the right application, as stated in the above quote, the rads do have to be sized for the correct flow temperature.

The current rads are not in there that long and i'm reluctant to go pulling them out. Is it a case that with these rads, I cannot use the bi-valent configuration that VRVIII mentioned earlier as the return temperature will not be low enough for the heat pump to work effectively??

[mad fridgie]

7 hrs/day - and yes, it turns off on int. 'stat.
26.37kW Firebird 7090 Heatpac

I presume that this covers the coldest days, so the max heating is 180kwhr/day, so size heat pump nominal 10Kw, as far rad sizes go, you have already shown that they are much bigger than actually required, so there is no problem in reducumg the the temp meet the daily load, (in theory nearly 340% larger than need be, why because all energy required is delivered in 7hrs)
Go for it, (make sure you increase flow rates through rads)

[borderfox]

I presume that this covers the coldest days, so the max heating is 180kwhr/day, so size heat pump nominal 10Kw, as far rad sizes go, you have already shown that they are much bigger than actually required, so there is no problem in reducumg the the temp meet the daily load, (in theory nearly 340% larger than need be, why because all energy required is delivered in 7hrs)
Go for it, (make sure you increase flow rates through rads)

Thanks madfridgie. If I work on the basis of a 10kW pump, do you have any specific pump recommendations?

[mad fridgie]

Thanks madfridgie. If I work on the basis of a 10kW pump, do you have any specific pump recommendations?

On this one i really can not help, your selection in Europe is much greater than here. As a general rule look for a well branded name, Japanese or European,
The some of chinese ones technically can be good, but Friday afternoon tends to last until Thursday afternoon the following week.
Personally I would look for one with an electronic expansion valve, as these normally allow for smaller pressure differences (pretty technical)
With your type of installation, it is more to do with you installer/designer. If the set up is not right, the quality of the heat pump becomes less important.
read through all the treads and take note of some of the little gems of information that has been given.
Watch out for the b******t artist.
Good luck
Mad

[olddog]

Reading through this thread I cant figure out what technology you are planning to use. A2W or GSHP ?
If A2W, then in your design please expect COP to fall significantly as ambient falls. Also find out if / how defrost cycles are handled by whatever system you propose to install.
You may find that you will need to oversize the system significantly to be assured of reasonable performance in the event of "very cold" Irish weather

[mad fridgie]

Reading through this thread I cant figure out what technology you are planning to use. A2W or GSHP ?
If A2W, then in your design please expect COP to fall significantly as ambient falls. Also find out if / how defrost cycles are handled by whatever system you propose to install.
You may find that you will need to oversize the system significantly to be assured of reasonable performance in the event of "very cold" Irish weather

He is looking for an air source system, with his existing boiler as a back up, so no need to over size.

[olddog]

He is looking for an air source system, with his existing boiler as a back up, so no need to over size.

Ah, I see

Good job somebody is paying attention

[pauricconnolly]

Air to water with back up boiler for extremely cold ambient ,
Heat pump on low temp radiators with correct controls in place.
Would also recommened you inspect your house insulation(cavity insulation,attic insulation and bring up to current building regs).
Some v good air -water heat pumps on the market at the moment but on the other hand some nightmares out there also .

[freezetech]

these ashp still give a cop of 1-2 at -10 thats still better than any oil boiler

[mad fridgie]

these ashp still give a cop of 1-2 at -10 thats still better than any oil boiler

You need to be very careful, you need to focus on system/process/capital cost/diversity.
COP, remember that most manufactures do not show defrost requirements in performance data (because it makes the machine look bad). When the ambient is cold on rad system you need warmer water for quick response, which reduces the COP. Do not sucked in by your heat pump sales rep.
If we look at this case.
Boiler is already there (no further capital cost)
New small heat pump works 80% of time X cost.
If you decided to increase the heat pump to cover 100% then cost would increase by X + 50%.
Now at the low ambient 20% the COP of aheat pump is lower, so the saving between the boiler and heat pump is reduced. The 50% / (saving * 20%) gives payback for the upsized machine, this will be 10s of years. withoout knowing all costs i would guess the payback would be greater than the like of a machine.
"law of deminishing returns)
mad

[olddog]

these ashp still give a cop of 1-2 at -10 thats still better than any oil boiler

In addition to Mad Fridgies points, in Ireland a kWhr of electric power is much more than twice the price of a kWhr of heat from oil. So oil boiler wins handsdown over ASHP with COP 2

As pauricconnolly says, check the building regs : apart from the BER nonsense there are now a whole heap of crazy regs concerning oil boilers, their setting up and zoning

Do send a note to minister Gormley to thank him for the endless fun that you have as you go through all this stuff