Advice needed on ASHP

[sambotc]

F.B you may not require a full re-design if you opt for a gas boiler replacement but without seeing the system it is hard to tell what is wrong. You would almost certainly require a full redesign if you opt for a heat pump as all the radiators will most likely be undersized. If I remember your house is of fairly new construction so the radiators are unlikely to be over sized unless recent additions such as cavity wall and loft insulation have reduced the heat loss. Even then I would think not by enough in most rooms.

i couldn't tell you what the heat pumps reliability is like, it is fairly common technology as said, but my fridge doesn't run 24/7 it cuts in and out depending on temperature, and given its well insulated construction, this isn't all that often.

when you look at carbon reduction, somewhere around a cop of 2.5 will match that of a gas boiler so in theory an air source heat pump could reduce carbon when compared to gas, but in practice this will drop as the days get colder so depending on outside weather factors you could very well find swapping from gas to a heat pump is counter productive in these terms especially taking into account the pasteurisation cycle.

dont get me wrong the technology works and could be excellent in the right circumstances, but in my opinion replacing a gas boiler, or being able to claim rhi in doing so is wrong.

 

[The Solar King]

Why not go the whole hog and install a GSHP? At least that way you minimise the issues of performance as ambient temperatures fall away in the heating season. I have yet to be convinced as to the efficacy of ASHPs, they are after all little more than the back end of an air conditioning unit. Once the investment is made in a bore hole or ground array, it is there for good. It's cost needs to be considered over a far longer period than the heatpump itself. Cost can be a barrier which is why ASHPs are currently more popular.

 

[FB.]

F.B you may not require a full re-design if you opt for a gas boiler replacement but without seeing the system it is hard to tell what is wrong. You would almost certainly require a full redesign if you opt for a heat pump as all the radiators will most likely be undersized. If I remember your house is of fairly new construction so the radiators are unlikely to be over sized unless recent additions such as cavity wall and loft insulation have reduced the heat loss. Even then I would think not by enough in most rooms.

I made a sketch for a plumber/heating engineer friend of mine. It'll give you lads a real-world "case study" to practice on.
See pic below. Radiators marked in orange, with approximate dimensions of the rads in feet to the right of the plan (3.3ft to a metre for those young 'uns among you).
Edit: ceiling height 7.5ft (2.3m).
Also shows "typical" "average" temps in each room, with the lounge at 21'C. With changes in wind direction the lounge can go up or down 0.5'C and the diner will do the opposite (e.g. 20.5'C lounge and 23'C diner or 21.5'C lounge and 22'C diner).
Heat-up time is about 1'C every half-hour. Lowering the dining room rad to balance with lounge makes this 1'C every three-quarter-hour.

Note undersized lounge radiator.
Note North-West-ish-facing front of Lounge which gets less sun and catches more of the UK's prevailing wind (wind direction can change room temp by 1'C).
House is detatched and in a rather open landscape.
Walls are regular brick cavity, dry-lined. Unsure of wall insulation as my old house (built slightly earlier and in a nearby street) had blocks of fibreglass slipped into the cavity (we found this when we had a window changed to a patio door). We don't know what's inside the cavity of our current house.
Loft has about six inches of insulation, which is covered by loft boards (so probably acts a bit like a cavity).
Also note issues with drainage for adding a condensate outlet due to kitchen door and position of drains.

 

[Earthstore]

There may be another reason why your lounge is colder, the rad is under the window, I am aware this is common practice however when it is hot it has no thermal mass above it to hold the heat (no brickwork just a window), all the other rads will warm up the wall above the rad acting similar to a storage heater.

I would just like to simplify this thread for some reading, because due to more government rules it may sound like rocket science to some.

The temperature you are trying to achieve is around 20 degrees, a gas boiler would run at around 65 degrees, taking into account some system heat loss your rads would be around 55 degrees.
If you change to a heat pump they run at lower temperatures, so to maintain the 20 degrees you require you need to have reasonable insulation, the less heat you let out the less you have to put in, also to warm the rooms from cold you would need a larger surface area of rad to heat the same room space because they would be running slightly cooler, still a long way from the 20 degrees you are trying to achieve though.

I have seen several different heat pump systems here in the UK, and most are working very well, some had initial problems but this was due to install plus fine tuning as they are quite complex, sadly the worst one is a local authority house, installed by people that do not understand how they operate so the plumbing/wiring was all quite shocking really.

As to the running costs, I can give a direct comparison here, two friends of mine have similar houses, one is slightly older and uses oil to rads, heating costs £2500 per year, and it is not too warm in there.
The other house is new, well insulated, underfloor heating and a ground source heat pump fitted, heating cost £900 per year, and it is very warm in there. The system was not without its problems in the first 6 months though but well worth the hassle.

The advantage of an ASHP is that it stands outside and if you choose the right make they are very quiet, but for a GSHP you have the added cost of installing your ground collector, whether drilling or laying a grid, plus the inconvenience and mess, you will also need a plant room to put the heatpump and associated hardware.

So normally, not always but normally, ASHP is best for retrofit, but GSHP is best new build.

One other thing that I would recommend, is to have your property surveyed with a thermal imaging camera, but by someone that knows what they are doing, it is a fantastic way to find out where the heat is escaping from your property and some of the remedies may not be too expensive.

I hope this helps.

 

[FB.]

There may be another reason why your lounge is colder, the rad is under the window, I am aware this is common practice however when it is hot it has no thermal mass above it to hold the heat (no brickwork just a window), all the other rads will warm up the wall above the rad acting similar to a storage heater.

Yes, the lounge rad is the only one sitting under a window. It is also under-sized, and apparently the lounge ought to have been fitted with two smaller rads to spread the heat more evenly rather than all at one end. The lounge rad faces the diner, but the dining rad is at right angles to the lounge.
The rads in the rooms other than the lounge are about correctly sized - both in theory and in terms of their ability to heat their rooms adequately.

The temperature you are trying to achieve is around 20 degrees, a gas boiler would run at around 65 degrees, taking into account some system heat loss your rads would be around 55 degrees.

Yes, I once stuck a thermometer on the rads and they get to a little over 55'C on the outside and probably 60'C water inside.

 

[jason121]

could do with a few more measurements like windows and hall and clock room dimensions but here goes
Dining room 1213 watts loss
Lounge 1496 watts loss
kitchen 936 watts loss

 

[sambotc]

What outside temperature is that based on jason121?

F.B do you have a fire in that chimney? Sometimes the specifiers took into consideration other heat sources and believe it or not reduced radiator sizing on the presumption the fire would supplement.

as jason121 has said, more info needed to be accurate. floor construction, windows sizes and materials. Is the fireplace in use? does if have a throat/chair birck or is it open?

 

[jason121]

-3 didnt spend a lot of time on it just did a quickie

 

[FB.]

What outside temperature is that based on jason121?

F.B do you have a fire in that chimney? Sometimes the specifiers took into consideration other heat sources and believe it or not reduced radiator sizing on the presumption the fire would supplement.

as jason121 has said, more info needed to be accurate. floor construction, windows sizes and materials. Is the fireplace in use? does if have a throat/chair birck or is it open?

Yes, the black block on the left of the lounge is a chimney. It is not open at present in order to reduce draughts in the already-cold lounge, but we do open it up and use it at Christmas for effect.
There is an unused (never been used) gas point beside the fireplace, so that a gas fire could use the chimney as an exhaust.

Floor is concrete (house sits on about a 6ft thick concrete raft), with carpet on top of the floor.
All windows are double-glazed, wooden frames.
Diner has 1.8m wide x 1.9m high (6ft x 6.5ft) double-glazed, full-glass, double patio doors.
Lounge has a 1.8m wide x 1.3m high (6ft x 4.25ft) double-glazed window.

 

[FB.]

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Mmmmmmm a lovely open fire at Christmas. :carolers:




Just don't tell the CO2 inspectors.

:behead:-


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