Archive for Downsizer For an ethical approach to consumption
 


       Downsizer Forum Index -> Energy Efficiency and Construction/Major Projects
MikeB

Plumbing

Hi all

My family and I have just purchased a derelict croft in Caithness, we are building a 4 bed timber framed house and are looking for some input on the heating and plumbing.

We intend to install a heat pump as we have plenty of land, our living room will have multi fuel burner and we would like a back boiler to help warm the water, we are also toying with the idea of solar water heaters on the roof.

Questions:

Is it worth installing all three systems

Does anyone have any practical advice on how to mate all three together

Thanks in advance

Mike & family
gil

Hi there, and welcome to Downsizer.
Folk who know about these things will be along shortly...

Whereabouts in Caithness ? Not nearly as many derelict crofts there as 10 years ago. I nearly went to look at a farm in Watten a few months back.
dougal

Re: Plumbing

MikeB wrote:
... We intend to install a heat pump as we have plenty of land, our living room will have multi fuel burner and we would like a back boiler to help warm the water, we are also toying with the idea of solar water heaters on the roof.

Questions:

Is it worth installing all three systems

Does anyone have any practical advice on how to mate all three together
...

Hi Mike, and welcome!

I'd suggest that you*don't* tie in all the systems.

The heat pump works best at the low temperatures used for underfloor heating. Its CoP falls right off at higher (domestic hot water & radiator central heating) temperatures. Down IIRC to 2 ish. IMHO therefore better to use Economy7 straight (if needed) for water heating rather than spend loads for a small benefit.

You can very simply have a hot water tank that is heated both by solar (so solar-only in the summer) and the multi-fuel stove (almost exclusively) in winter.
The same tank could have a couple of immersion heater positions - one for E7 and maybe a second for a future wind turbine energy dump.
A bigger tank with thicker insulation would be better (so you can store more energy day to day), and you'd probably only have the E7 immersion heating a small volume at the top of the tank, to tide you through poor (but not cold enough to light the stove) weather...

Depending on the heat output of the stove, you might also be able to run a few radiators off it. But I don't see advantage in the complexity of linking that circuit (in any way) to the underfloor from the heat pump.

People such as Navitron http://www.navitron.org.uk should be able to help with an appropriate tank (and evacuated tube collectors, and...)
It would give cheap development flexibility to have as many extra coils, element inserts, whatever on the tank from day one - such things are much more expensive to try and add later!
tahir

Welcome on board Mike, I'm sure you'll enjoy it here.
MikeB

Thanks for the warm welcome

Our place is in Mybster, your right about the amount for sale and the prices are starting to rise dramatically.

Tahir, thanks for that, I take it you got your delivery ok???

What would you say was the most efficient way of heating the house, radiators or under floor, to be honest I personally would like radiator as I fine warm floors uncomfortable.

The heat pump runs at apox 2 Kw so I wanted to offset some of the running cost by keeping the water hot from another source and thought the multi fuel and solar would keep it toped up thus lowering our need for electricity to run the heat pump

Mike & Family
tahir

MikeB wrote:
Tahir, thanks for that, I take it you got your delivery ok???


Yeah, ta Wink
tahir

The thing with heat pumps is that they need a low temp system to be effective, rads need water at a relatively high temp, that's why heat pumps are normally used with underfloor.

Dougal (and others) know much more about this so I'll leave it to them
Treacodactyl

MikeB wrote:
What would you say was the most efficient way of heating the house, radiators or under floor, to be honest I personally would like radiator as I fine warm floors uncomfortable.


Not much to add but I've often wondered how reliable underfloor heating is, i.e. if leaks might be a problem. I know it's been around for ages now and many people have it but an 'old fashioned' copper pipe and rad set-up can occasionally leak and is easy to fix but what about underfloor?
dougal

tahir wrote:
The thing with heat pumps is that they need a low temp system to be effective, rads need water at a relatively high temp, that's why heat pumps are normally used with underfloor.


Yes.

Heat pump efficiency is stated as the CoP (coefficient of performance).

This is the ratio between the amount of energy that is used to run the pump, and the amount of energy that comes out from being pumped.

If the pump is using 2kw, you might hope to get 8kw of heat out of the thing. (ie a CoP of 4).
Different salesmen will claim different numbers, but 4 is a fair starting point I think.
HOWEVER that efficiency depends on the heat pump working at a temperature difference of 30C or less - that's the temperature difference between the outdoor collector circuit (arriving at the pump) and the indoor (hot) output to the heating circuit.
The greater that temperature uplift by the pump, the lower the efficiency that it can achieve (view that as either the less heat you can get out, or the more electricity used for the same heat output.)

Underfloor heating works well with a 35C (maximum) supply. Not that the floor should be "hot", just very comfortably warm to bare feet.
Radiators get about 80C from a traditional boiler, 55/60 from a condenser - which is why bigger radiators are specified with condensers.
You'd need massive radiators to run from a 35C supply.
And a heat pump is an expensive means of getting even 55C, and an even worse way of shooting for 80C.

There is another advantage of underfloor.
Putting the pipes into a large lump of concretey stuff (maybe with lime...) allows the thermal mass of the floor to be used as a gigantic storage radiator. And in turn, that allows a heatpump system to run largely on E7. So with a CoP of 4, each kwh of heat is costing you 1/4 of the E7 rate. Which is cheap enough to pay back against an oil or stored gas system.
Running at a CoP of 2, on peak rate power doesn't make any sort of sense.

It should be obvious that an underfloor system is not the sort of thing that you turn on as you come in from work. If you tried that, you might well have 'hot' floors while complaining that the house was cold.
It is intended to be run steadily throughout the heating season. Rather like an Aga.
Its slow to respond. But cheap to run (on 1/4 price of E7...) - totally unlike an Aga! Very Happy

Also, and especially because its a 24 hour thing, it really goes hand-in-hand with super-duper insulation.
And it would expect it. 8kw (less than 3 electric kettles) is not very much heat for a 4 bedroom house in the North of Scotland.

And in that regard, you might be checking that your multi-fuel stove can be installed as 'room-sealed' so that it draws its combustion air from outside, rather than the inside of the house. Controlling ventilation and minimising air leakage are going to be important. You might even be considering installing a heat recovery system...
Quote:
The heat pump runs at apox 2 Kw so I wanted to offset some of the running cost by keeping the water hot from another source and thought the multi fuel and solar would keep it toped up thus lowering our need for electricity to run the heat pump
Don't have the heat pump heating water to 50C and beyond for hot water. I suggested above that your hot water needs are likely best supplied from summer solar (rather a lot of spring and autumn too with enough evacuated tube collectors) and winter from the stove, with occasional topping up when it happens to be needed with economy7. Doing the topping up with direct E7 rather than the heatpump won't add much to the running cost and should make the installation rather a lot simpler, and so cheaper.
James

heat pumps can also be used with large (panel) radiators and in some circumstances, you may decide that these large radiators are better (ie personal preference comes into play, or you want to be able to maintain them). But if your starting from the bare bones up, under floor is the most efficient. As dougal said, the big advantage is that they slowly leak out their heat into the big slab of concrete floor which maintains the ambient room temperature, instead of actively heating (like a traditional radiator does).

A third way which I'm seeing coming into building design recently is via the use of cooled/ warmed beams within the constructions. Effectively, the building materials themselves become the heater.

There are a couple of companies I've heard of that suggest you can run a heat pump purely as a pre-heater to feed your hot water system (so the water entering you hot water tank is at 30c, not 12c)

Personally, I'd keep the heat pump working in isolation. Work out the kilowatts required to heat your house for around 80-90% of the time, size it accordingly and use under floor heating as dougal suggested. Then top up on cold days with a solid fuel burner (wood stove). Then solar gives the hot water, maybe having a dual tank plumbed into the woodstove.

Are you thinking of a slinky or a borehole (if so, open or closed loop?) If you've got loads of land, a slinky is probably the way forward.

A word on the CoP's- its very hard to empirically prove these figures. Therefore its very easy to state a figure which cannot be disproved. In general, the CoPs stated on US derived equipment appear less likely than Swedish equipment. I base this purely on what I've been told by a UK research academic who has been reviewing this field for some years now.
MikeB

As we have the space a slinky system is the way we were heading, were told two trenches 20m long by 1m wide and 1m deep. This is in an area where the water table is only 600mm down and that this should enhance its efficiency.

I am getting various reports on how long heat pumps take to warm up, I wanted something that would warm up quickly and I do not think the under floor heating will suffice, any idea on how long a concrete pad warms up as opposed to large radiators
scoop

We went through a similar process year ago but in our case we bought an old cottage. After lenghty research we came to the following conclusions:

1) Combining heat from various sources was just too complicated.
2) A ground source heat pump would be of no benefit in an old cottage because with the best will in the world we could not insulate it to the point where the heat loss would be replaced by the energy harvested from the GSHP.
3) Our inherited propane fuled combi boiler which uses a sealed system could not be connected to our proposed wood fired boiler whcih required an open vented system.
4) It would be much easier and cheaper to run separate systems.

So we ended up keeping our existing propane combi boiler and radiators and installing a second heating system for the wood burner (Charnwood 14B). The combi provides a short burst of heat in the morning when the family get up to go to work / school. The Wood burner heats the house in the evenings and weekends. The wood burner currently supplies 5 radiators with another 2 shortly to be added. We have been very happy (and warm) with the results.

Its sounds like an expensive option but excluding the wood burner the whole system cost 600 to install using a week of my fairly limited diy plumbing skills.

Chris
       Downsizer Forum Index -> Energy Efficiency and Construction/Major Projects
Page 1 of 1
Home Home Home Array Home