A bit of a complicated system set up

[vetinry]

Morning everyone

I am in the midst of renovating a property that we bought last year and (probably a little too late) am now considering options for the central heating and hot water.

Currently the house (approx 3000 sq ft, built in 1987) heating and hot water is supplied by an oil boiler (Boulter Camry 5?).

Heating

The central heating is "Y" plan and a single zone, and before we moved in, all rooms (14 of them) were supplied by radiators. There was insulation in the various loft spaces but I have been topping it up as and when there is an offer at B&Q - I'm aiming for min 300mm but it is actually deeper than this in some places.

We have already renovated the Kitchen and opted for Wet underfloor heating under a tiled floor and over 70mm insulation to achieve u-values.

Underfloor heating is not an option everywhere in the house because we want to put carpets and not have to worry about low tog values.

In one of the upstairs bedrooms, I am about to install skirting board heating to see how I get on with that.

And in the upstairs bathroom, we want to tile so we are considering either wet or electric underfloor heating.

Domestic Hot Water

The water is supplied by a cylinder, which I think I calculated as about 160litres and which seems to be a little bit small for a 5 bedroomed house.

In addition, the immersion heating is broken, and the cylinder is built into the eaves of upstairs making it's removal without removing the tank rather difficult.

In the upstairs loft, there are 2 huge water tanks (gravity system) and there are 3 shower pumps scattered throughout the house.

When the house was built, copper must have been pretty cheap because there are literally hundreds of metres of copper pipe running through the loft spaces. For example, each of the 3 showers are fed by their own 22mm supply and they are scattered throughout the house.

The hot water is also linked to a secondary circulation system due to the sheer distance that water has to travel to the various tap points.

I've checked mains pressure (about 4 bar) and flow (about 25 litres per minute)

Just before Christmas we had an oil delivery and 2500 litres at 75p per litres gave me a bit of a shock.

And now, I'm going to need a little bit more oil to get through the summer (boiler still supplying hot water)

Therefore I'm researching different options, principally to reduce our demand on oil and improve efficiency

Questions

I have some fairly basic questions which I hope you might be able to help with

How much of the oil is being used to heat the property vs hot water production.
Is it very inefficient to have a DHW system which runs seperately from the CH. I've seen an indirect cylinder with built in air source heat pump which looks like it could supply all of my hot water at a fraction of the cost that I currently spend on oil
If the oil boiler is on, does it make any difference whether it is heating lots of rooms or just a few? The reason I ask this is that I will still need to heat the underfloor heating, and rooms with carpets where radiators or thermal skirting will be used. But in the bathroom, for example, it would be much less expensive to install electric underfloor heating but if the boiler is already on, am I just spending twice on energy?
Seperating the house into zones. I definitely want to zone off the kitchen ufh but wondered how close to the "centre" of the system the zone valves need to be placed. ie could you have the zone valves operating close to the rooms or is this inefficient since you are still heating pipework prior to the zone valves?

Really hope that you might be able to shed some light on all of this

Thanks

Steve

 

[electronicsuk]

How much of the oil is being used to heat the property vs hot water production.

That depends on how much hot water you consume, and how often you run the central heating. Best keep an eye on your oil consumption summer vs winter to answer this one.

Is it very inefficient to have a DHW system which runs seperately from the CH.

No, there's nothing inherently inefficient in using a boiler to heat the DHW cylinder alone. There will obviously be savings to be had by investing in a condensing boiler and well insulted cylinder with quick recovery coil, as there's no point in heating a cylinder and letting all that energy escape into the atmosphere if the water isn't drawn off.

I've seen an indirect cylinder with built in air source heat pump which looks like it could supply all of my hot water at a fraction of the cost that I currently spend on oil

I'm not sure how good these are, as I imagine they can't achieve the water temperatures you might be accustomed to. However, at 75p a litre, I suspect you may be right in that it could pay for itself relatively quickly.

If the oil boiler is on, does it make any difference whether it is heating lots of rooms or just a few?

Yes, more energy is required to heat more rooms, hence more oil will be consumed when you're running more radiators.

The reason I ask this is that I will still need to heat the underfloor heating, and rooms with carpets where radiators or thermal skirting will be used.

I have to wonder if UFH was really a wise choice with an oil boiler, given that it needs to be left running for significant periods of time to heat the mass of the flooring. Perhaps you would be better looking into a ground source heat pump and UFH throughout the property?

But in the bathroom, for example, it would be much less expensive to install electric underfloor heating but if the boiler is already on, am I just spending twice on energy?

Direct electric heating is one of the most expensive forms of heating. I believe 1 litre of heating oil will give up around 12kWh, so with an 80% efficient boiler that's just a tad under 10kWh of heating energy available for every 75p spent. Ergo, the cost of your oil is about 7.5p/kWh. Peak rate electricity is 13p/kWh. Go figure.

Seperating the house into zones. I definitely want to zone off the kitchen ufh but wondered how close to the "centre" of the system the zone valves need to be placed. ie could you have the zone valves operating close to the rooms or is this inefficient since you are still heating pipework prior to the zone valves?

Zoning the system is a good idea. It makes no difference where the valves are*, as when they're closed, there will be no flow throughout that section of the system, so the pipes leading to the valve won't be heated either.

*Valve placement needs to be considered to prevent reverse circulation through the system, although not relevant in terms of your question.

 

[vetinry]

Thanks Matthew

Some really helpful information in there.

And a great little calculation to show that even at current prices, oil isn't probably anymore expensive than direct electric.

I don't have economy 7 and so I probably am paying about that for electric.

As for my boiler still being 80% efficient, I think it's getting on a bit now so probably not.

I will continue to investigate new cylinders but perhaps having it heated by oil isn't as bad as I thought. I was wondering whether just using an immersion heater in the summer would be more efficient than having the boiler fire up in the morning and evening.

Steve

 

[electronicsuk]

An immersion on standard rate electric definitely won't be cheaper to run than oil, but may be worthwhile on an off-peak tariff.

Although a heat pump requires electricity, they generally have coefficients of performance of somewhere between 3 and 4:1, such that 1kWh of energy consumed can output as much as four times that in heat. Beats direct electric heating hands down, although typically flow temperatures are quite low, so for the system to work properly you either require UFH or oversized radiators in all rooms.

 

[obiplumbkinobi]

Consider GSHP if you have the land

 

[vetinry]

I'm thinking that I might struggle to heat the property with a heat pump (either ground or air) because of those low temperatures. I'm not planning to put UFH everywhere, and we don't really want huge radiators taking up valuable wall space.
So, I'm probably going to continue with oil for the heating but ensure that the house is properly zoned to allow a much greater degree of control, and I may look at an alternative energy source such as wood at some point.
As for the water, perhaps I should look at the ASHP option to just run DHW, perhaps with oil as back up (or standard immersion heater)

Steve

 

[electronicsuk]

Also make sure that DHW recirculating loop is well insulated - fit the thickest lagging that's practical to do so, otherwise you'll be losing a lot of heat.

 

[Agile]

I would be considering using a generator from the heating oil and recovering the waste heat to use in the house. That makes it about 95% efficient compared with power stations which waste the 66% of heat they produce.

 

[vetinry]

Hi Agile
Can you explain that a bit more please. Are you suggesting trying to capture some of the oil boiler exhaust heat, or heat from inside the house?

Thanks

Steve

 

[mointainwalker]

I definitely want to zone off the kitchen ufh but wondered how close to the "centre" of the system the zone valves need to be placed. ie could you have the zone valves operating close to the rooms or is this inefficient since you are still heating pipework prior to the zone valves

My house has three zones ( each a separate floor) and each zone has three or four or five circuits. I have control valves on the (zone ) feed pipes out of the boiler controlled by a thermostat on each floor.

Controlling each circuit is possible but expensive because of the actuators which would be fitted on the manifold on each floor plus a thermostat* for each zone which would be 12* instead of three for me.

Since the pipes are in the screed from when they leave the manifold, not feasible to fit circuit-valves anywhere other than centrally