Is oil and rads wrong in a low energy air tight house. ?

gooner99

It seems to be a given that if you build a passive or near passive house you should go with a heat pump and underfloor. But if you were to build to passive or near passive standard with a low heat demand, could it make sense to heat the house using oil and rads. I know underfloor and heatpumps were ridiculed during the boom, but when you look at thier appilcation, they were installed in poorly insulated and leaky houses. So in contrast would is it wrong to ignore oil and rads in a highly insulated and airtight house?

Metric Tensor

Nothing at all wrong with it. In fact with the current price of oil it is probably the cheapest way to heat your house if you are not connected to mains gas. It's also much more responsive and arguably Irish people will waste less money using oil because we are not good at leaving control systems alone!

However, if you are building a new house you have to have a certain amount of renewable energy generated on site so you will have to couple the oil boiler with something like solar panels. Heat pumps are (rightly or wrongly) counted as a renewable energy source themselves so sometimes you can get away without supplementing them.

FWIW OP - If I was building a house tomorrow I'd use oil and solar - although depending on prevailing technologies that could change fairly soon.

air

The lower a homes energy consumption the less that the heat source matters ultimately.
The arguments against oil and rads for me is as follows:

1. Rads take up valuable room space, as build cost per m2 increases, so too does the impact of the space they take up. Note that they often take up a lot more than their basic footprint due to forcing you to space furniture out from walls etc. They also look ugly in my opinion.
2. Vulnerability to future oil price swings and carbon / emissions taxation.
3. Requirement for annual servicing
4. Requirement for fuel storage and access route to same
5. Risk of fuel leakage or theft
6. High flow temperatures which may cause local overheating in a very well insulated home


I could go on but that's a good start. All that being said there's no reason to rule it out completely, it may suit some for their own reasons.

fash

Nothing wrong with it- in some super insulated houses they use electric heating only- the worst form of heating in theory.
Except it is cheap to install, you almost never use it and if you do you use very little.
Using oil in a reasonably well insulated house is a similar concept

air

fash wrote: »

Nothing wrong with it- in some super insulated houses they use electric heating only- the worst form of heating in theory.
Except it is cheap to install, you almost never use it and if you do you use very little.
Using oil in a reasonably well insulated house is a similar concept

Indeed, although the capital cost of installing an OFCH system is high relative to electric.

The homeowner needs to work out the annual kWh heat demand of their home & then work out which heat source is most economical over the medium to long term, taking into account capital and running costs.

Outkast_IRE

I think if i was in this situation personally i would probably take a hard look at the following.

In such an airtight house you will likely have a MHRV system, i would question if putting in a decent size stove and lighting it on the cold nights, the MHRV system heat exhanger will transfer enough of the heat from the warm air produced by the stove to heat the incoming air sufficently. Then use a few plug in electric items for backup.

Dardania

air wrote: »

fash wrote: »

Nothing wrong with it- in some super insulated houses they use electric heating only- the worst form of heating in theory.
Except it is cheap to install, you almost never use it and if you do you use very little.
Using oil in a reasonably well insulated house is a similar concept

Indeed, although the capital cost of installing an OFCH system is high relative to electric.

The homeowner needs to work out the annual kWh heat demand of their home & then work out which heat source is most economical over the medium to long term, taking into account capital and running costs.

To add to this point, if looking specifically at using oil & rads, I would plan for the possibility over that medium to long term that the heat source may need to change to something like a heat pump for one reason or another.
Ways to accommodate that would be by sizing rads for lower temperatures (e.g. oversizing them) so that in the short to medium term, works fine with a condenser boiler, and longer term, a heat pump can still utilise the rads (as heat pumps don't like higher temps)

delfagio

As the common theme here is that modern well insulated and airtight houses do not require much heating then heating can come from many options such as,

1) electric
2) oil condensing boiler
3) gas boiler
4) air source heat pump
5) ground/geothermal heat pump

Oil in my opinion is the preferred install and general lowest outlay costs. Approx 3k compared to Air Source of 10k and Geothermal of 20k plus.

Rads as mentioned already do take up much valuable wall space and can restrict room usage. Can look a bit of eye sore sometimes. UFH is very good and can be better for changing from oil boiler to heat pump in later years when heat pumps become cheaper, more efficient and economical viable.

I recently built well insulated airtight house and have oil condensing boiler with UFH upstairs and downstairs and currently use approx 250-300Euro per year on oil for heating 2500sq foot. Thermodynamic solar panel heats our hot water for approx 70Euro per year (just myself, wife and our baby of 4months).

gooner99

delfagio wrote: »

As the common theme here is that modern well insulated and airtight houses do not require much heating then heating can come from many options such as,

1) electric
2) oil condensing boiler
3) gas boiler
4) air source heat pump
5) ground/geothermal heat pump

Oil in my opinion is the preferred install and general lowest outlay costs. Approx 3k compared to Air Source of 10k and Geothermal of 20k plus.

Rads as mentioned already do take up much valuable wall space and can restrict room usage. Can look a bit of eye sore sometimes. UFH is very good and can be better for changing from oil boiler to heat pump in later years when heat pumps become cheaper, more efficient and economical viable.

I recently built well insulated airtight house and have oil condensing boiler with UFH upstairs and downstairs and currently use approx 250-300Euro per year on oil for heating 2500sq foot. Thermodynamic solar panel heats our hot water for approx 70Euro per year (just myself, wife and our baby of 4months).

I'd imagine if you heated your hot water with a combination of oil and immersion, your bill wouldn't be much more either. Sounds like a good combo.

gooner99

Outkast_IRE wrote: »

I think if i was in this situation personally i would probably take a hard look at the following.

In such an airtight house you will likely have a MHRV system, i would question if putting in a decent size stove and lighting it on the cold nights, the MHRV system heat exhanger will transfer enough of the heat from the warm air produced by the stove to heat the incoming air sufficently. Then use a few plug in electric items for backup.

I know someone with this setup in an approx 150sqm eco house holiday home. Small stove and solar panels along with mvhr. Stove also feeds the hot tank. The only rads are two towel rads.He did say that the stove takes about a day to get the house up to temp if he uses the house in winter. He said he could simply plug in a couple of electric heaters for a couple of hours, it's just the "eco" part that's stopped him for doing that. So just throws on a jumper for that evening.

Metric Tensor

gooner99 wrote: »

I'd imagine if you heated your hot water with a combination of oil and immersion, your bill wouldn't be much more either. Sounds like a good combo.

I was actually thinking the same thing and started doing a little calculation in my head to see what a oil/immersion hot water setup my cost over the year. But then I realised I'd need a pen, paper and more details so I moved on!

gooner99

Metric Tensor wrote: »

I was actually thinking the same thing and started doing a little calculation in my head to see what a oil/immersion hot water setup my cost over the year. But then I realised I'd need a pen, paper and more details so I moved on!

Ah, you would have had it done by the time you replied!

Metric Tensor

OK - very very very rough calculation.


Performance

Getting certified Coefficient of Performance figures for Solar Thermodynic systems seems impossible. But this website suggests an average of 1.85 ish.

This is much lower than many sellers advertise. They will undoubtedly tell you their tested/certified/non-certified/wishy-washy values if you ask but I'm using 1.85 because it's the only value that I could find based on any sort of test.

This basically means that the system is 1.85 times more efficient than a standalone direct immersion which has a COP of 1.0 (give or take).

delfagio spends E70 a year on the "solar thermodynamic system" **



Electric Immersion alone
This means that with an immersion alone it would cost 70 x 1.85 = E129.50 per annum so delfagio has (from this rough calculation) saved E59.50 per year by having this system as opposed to an electric immersion only.

If it cost E2000 more to install this system than an electric immersion it will pay for itself in 33 years (assuming it costs the same to maintain as an immersion ...)



Oil
A little bit of extra work required here.

Assuming the OP pays circa 20c per KWh for electricity means his system uses approximately 350kWh per year on hot water. With a COP of 1.85 this means that 350kWh comes from the electricity and an extra (0.85 x 350 297.5kWh comes from the "sun."

So it takes 350 + 297.5 = 647.5kWh to heat the OPs water each year.

I'm going to conservatively assume that an condensing oil boiler system and the pipework from it is 80% efficient. (N.B. - cylinder losses are the same for each system so this is just boiler efficiency and pipe losses).

This would mean that it would take 647.5 / 0.8 = 809.4kWh of oil to heat the water.

According to SEAI figures here there is 9.821 kWh per litre of oil.

This gives 809.4 / 9.821 = 82.42 litres of oil to heat the same amount of water. At 65c per litre this would give E53.57


Summary
Solar thermodynamic: E70.00
Immersion only: E129.50
Oil: E53.57


** Usage
delfagio's usage seems to work out at about 33 litres of hot water per day which seems on the low side. SEAI suggest about 40 litres per person per day. A scaling up of the above figures from 33litres per day to 120 litres per day for three adults would give:


Solar thermodynamic: E254.54
Immersion only: E470.91
Oil: E194.80



Note: It would be interesting to include in this calculation people who get hot water from their Air-Source heat pumps but I don't have the figures to hand.


P.S. - I should add that there is the possibility delfagios consumption figure is so low is because his unit is much more efficient than the figures I was able to find above. I haven't been able to find measured data indicating this level of efficiency though.

Metric Tensor

Delfagio - can I ask how you were able to separate the 70 euro figure from the rest of your electricity bill?

gooner99

Metric Tensor wrote: »

OK - very very very rough calculation.


Performance

Getting certified Coefficient of Performance figures for Solar Thermodynic systems seems impossible. But this website suggests an average of 1.85 ish.

This is much lower than many sellers advertise. They will undoubtedly tell you their tested/certified/non-certified/wishy-washy values if you ask but I'm using 1.85 because it's the only value that I could find based on any sort of test.

This basically means that the system is 1.85 times more efficient than a standalone direct immersion which has a COP of 1.0 (give or take).

delfagio spends E70 a year on the "solar thermodynamic system" **



Electric Immersion alone
This means that with an immersion alone it would cost 70 x 1.85 = E129.50 per annum so delfagio has (from this rough calculation) saved E59.50 per year by having this system as opposed to an electric immersion only.

If it cost E2000 more to install this system than an electric immersion it will pay for itself in 33 years (assuming it costs the same to maintain as an immersion ...)



Oil
A little bit of extra work required here.

Assuming the OP pays circa 20c per KWh for electricity means his system uses approximately 350kWh per year on hot water. With a COP of 1.85 this means that 350kWh comes from the electricity and an extra (0.85 x 350 297.5kWh comes from the "sun."

So it takes 350 + 297.5 = 647.5kWh to heat the OPs water each year.

I'm going to conservatively assume that an condensing oil boiler system and the pipework from it is 80% efficient. (N.B. - cylinder losses are the same for each system so this is just boiler efficiency and pipe losses).

This would mean that it would take 647.5 / 0.8 = 809.4kWh of oil to heat the water.

According to SEAI figures here there is 9.821 kWh per litre of oil.

This gives 809.4 / 9.821 = 82.42 litres of oil to heat the same amount of water. At 65c per litre this would give E53.57


Summary
Solar thermodynamic: E70.00
Immersion only: E129.50
Oil: E53.57


** Usage
delfagio's usage seems to work out at about 33 litres of hot water per day which seems on the low side. SEAI suggest about 40 litres per person per day. A scaling up of the above figures from 33litres per day to 120 litres per day for three adults would give:


Solar thermodynamic: E254.54
Immersion only: E470.91
Oil: E194.80



Note: It would be interesting to include in this calculation people who get hot water from their Air-Source heat pumps but I don't have the figures to hand.


P.S. - I should add that there is the possibility delfagios consumption figure is so low is because his unit is much more efficient than the figures I was able to find above. I haven't been able to find measured data indicating this level of efficiency though.

Thanks. Useful comparison.

BryanF

Should we factor environmental cost (co2/tons) into these figures?

How will oil fare against Grid electroc for example

Are we accounting for the BER renewable requirements ?

Metric Tensor

My calculation (if it could even be called that) was a financial one only.

No account taken for tonnes of CO2 produced.

Although it goes without saying that the 1 Vs 1.85 efficiency translates directly to tonnes of CO2 for the immersion and "solar thermodynamic" as they are both powered by grid supplied electricity.

gooner99

BryanF wrote: »

Should we factor environmental cost (co2/tons) into these figures?

How will oil fare against Grid electroc for example

Are we accounting for the BER renewable requirements ?

Of course Part L on new builds will result in some form of renewable being used (or at least planned for). But for refurbs it might throw the cat among the pigeons.

Casati

I think one of the big factors often missing from the calc's are servicing and repair costs for heating systems.

For example I was told by an Irish solar manufacturer that I needed get their solar tubes serviced annually (at a cost of circa 260 quid) to keep the warranty. I obviously didn't get it serviced and then in year three an error forced me to get their service engineer out - 340 quid for the pleasure.

I presume that Heat Pumps also have service or repair costs but I can't find information on that

Oil - as we know generally v reliable for 20+ years but needs an annual service - 60/80 quid seems to be the going rate

Electric only heating i would presume needs no servicing at all? I might look at this - anybody know roughly how installation and running costs of storage heaters compare?

Im starting another build shortly and my head is already wrecked going through all the options!