Do U-Values matter

fclauson

There is always a lot of questions on the board about U-Values, levels of insulation and airtightness etc so I thought I would share this with you all - I have been modelling my new build for some time - and have recently adapted the PHPP spread sheet with a small bit of VB code to allow me to loop through various U-value settings and to see what my Kw/M2/Year. It will also show me my BER rating (having taking the DEAP excel version and cross loaded it with data from PHPP)

So with this it shows something quite interesting

Based on 0.6 ACH
a Wall 0.1, Floor 0.1, Roof 0.1, Window 0.8 with glazing of 0.6
Kwh/M2/Annum = 13 (below the magic 15 - so no significant additional heating required)

but if I build a
wall of 0.18, Floor of 0.18, Roof of 0.18, windows 1.6 with glazing of 1.6
Kwh/M2/Annum = 48
so for this (despite the airtightness) you will need to push somthing like 1500 litres of oil (based on a lot of energy efficiency assumtions in the heating system) past the building each year to heat it.

If you then change the ACH to 3
for the first case 28.4
and the second 62.8

So the conclusion - well - you cannot guess at what impact the various elements have with out modelling it all.

Just thought I would share so those who are struggelling with "does it all matter" have some numbers to look at

sinnerboy

Exactly. U values are only one part of the mix.

BryanF

its the hierarchy that matters, building fabric first.. etc
IMHO deap is not great to look at your issue, consider what CABE has said on how the energy consumptions/gains are rated.

Mellor

Everything matters, each one perfected alone is useless if the others areas are lacking

gears

As others have said viewing modern construction simply in terms of u-vlaues is missing the point, the best description I have heard is that it's more a holistic approach that needs to be taken.

sinnerboy

It is noteworthy to re state / re present the impact of Air Tightness

Looking at the 2 option only

Kwh/M2/Annum = 48 at Passive house Standard (0.6)
Kwh/M2/Annum = 62.8 at "Good" Standard (3)
Kwh/M2/Annum = 14.8 difference

So if the house is 250m2

( area X difference x factor for fuel efficiency of boiler x storage and distribution losses x €oil

250 x 14.8 x 1.1* x 1.1* x 0.10 = €447.70 extra for heating ( hot water not included ) every year. ( If oil prices don't rise )

Of course U Values are important.

Don't neglect air tightness.

fclauson

and building on Syd's numbers

if oil rises 10% a year (my chrystal ball tells me these type of facts )

then his 447.70 cost in year one adds up to €28,000 over 20 years

I have not discounted out the interest you would pay on this from a mortgage etc - but an additional 10% on your build in year 0 (say €25k on your 250sqM build at the nominal rate of €1000/sqM) - and €25 buys a lot of U-value/airtightness prevention materials means its

a) probably a good investment to get that additional U value/air tightness benefit day 1
b) protects you from my 10% oil price above being just wrong (there just might be a flaw in my chrystal ball :mad:)
c) does your bit to save the planet
d) save you getting an early onset of rheumatism and arthritis from the draughts

fclauson

Have played with this further

if this build was built at current regulations it would use

112Kwh/M2/year
:mad::mad::mad::mad::mad::mad:
So conclusion - with attention to airtightness and insulation I can reduce my heat demand by 80+%

sinnerboy

Which also underscores the foolishness of undertaking the biggest financial burden of your life without seeking professional guidance. The internet is no substitute.

Carlow52

sinnerboy wrote: »

Which also underscores the foolishness of undertaking the biggest financial burden of your life without seeking professional guidance. The internet is no substitute.

i thought when you hear " I do" crystalised the biggest financial burden of your life.:D

The title on the post is a bit irish daily starish which is a bit disappointing in this serious side of the forum.
The discussion is not just about u values but about ach/at/insulation.

Nice to see SB has morphed into Syd

..and building on Syd's numbers..
then his 447.70 cost in year one adds up to €28,000 over 20 years

You can cut all the VB code u like and look at as many crystal chandeliers u like but if the specified products are not used properly in accordance with the various certs and required building practices then its all for nothing.

25k will buy a lot of AT/insulation measures but it needs to be installed properly.

I have said this before but when u see a builder using exp foam to seal triple gazed windows....

fclauson

Carlow52 wrote: »

i thought when you hear " I do" crystalised the biggest financial burden of your life.:D

The title on the post is a bit irish daily starish which is a bit disappointing in this serious side of the forum. ....

Hmm - and your comment about burden of you life is not !!

Carlow52 wrote: »

Nice to see SB has morphed into Syd

Typo accepted

Carlow52 wrote: »

You can cut all the VB code u like and look at as many crystal chandeliers u like but if the specified products are not used properly in accordance with the various certs and required building practices then its all for nothing.

25k will buy a lot of AT/insulation measures but it needs to be installed properly.

Totally agree

Getting back to my OP - at design stage you have to think about the factors which will create a performance build - and there are a number of these.

sinnerboy

Play the ball not the man guys...or the thread will be locked.

sinnerboy

fclauson wrote: »

and building on Syd's numbers

I've been called worse

sydthebeat

Carlow52 wrote: »

Nice to see SB has morphed into Syd
..

quite a compliment!!!

Slig

U-values have their place but its all down to workmanship and detailing, having a wall made completely out of polyurethane board will probably give you a great U-value until its washed away or blown down.

I think insulation has gotten way too much spotlight and drawn too much attention away from the other essentials like correct ventilation and moisture proofing.

AMG86

Three aspects - ventilation, insulation and air tightness - must be addressed as a package. They impinge on each other.

fclauson

Thought I would share this with you all - have developed the PHPP/DEAP spreadsheets further so you can compare prices for each build

take the same build make up @ the same U values @ an oil price of 80c/litre which increases 8% per annum for 15 years

This tables shows how much saving over 15 years you could get

target build @.6 ACH €-
target build @ 1 ACH €1,367
target build @ 2 ACH €4,932
target build @ 3 ACH €8,688
target build @ 4 ACH €12,607

So you can analise if its worth spending 12K to move a house from 4ACH to 0.6 or spendning 1.3K to move from 1 to .6

puts a price value on doing airtightness

Of couse this makes lots of assumptions but it all helps to show you if spending €€€ on an airtightness program is worth the effort

and remember the price of oil may fall as well as rise :eek::D:p

galwaytt

fclauson wrote: »

Thought I would share this with you all - have developed the PHPP/DEAP spreadsheets further so you can compare prices for each build

take the same build make up @ the same U values @ an oil price of 80c/litre which increases 8% per annum for 15 years

This tables shows how much saving over 15 years you could get

target build @.6 ACH €-
target build @ 1 ACH €1,367
target build @ 2 ACH €4,932
target build @ 3 ACH €8,688
target build @ 4 ACH €12,607

So you can analise if its worth spending 12K to move a house from 4ACH to 0.6 or spendning 1.3K to move from 1 to .6

puts a price value on doing airtightness

Of couse this makes lots of assumptions but it all helps to show you if spending €€€ on an airtightness program is worth the effort

Now that IS interesting, I often wondered about that myself. I saw a prov BER last week that came out at 28.24kWh/m2/yr, based on ACH of 2. So, if, as I hope, it actually comes out around 1 or lower, there should be a 'quantum' leap in consumption and savings ?

fclauson wrote: »

...and remember the price of oil fall as well as rise :eek::D:p

I'll belive that when I see it !! (motoring perspective, ignoring all else !)

sinnerboy

Quick and dirty calc for infiltration losses

volume x air change rate x delta t x specific heat capacity of air

example

Floor area 200m2. Average Height 2.5m = Volume 500m3

air change rate (test ) = 5 . Divide by 20 for air change at normal pressure = 0.25

Delta t . ( Bear with me )

Take indoor temp at 20 kelvin ( celcius )

Average year round temp in Ireland is 9 degrees so Delta t is 11
x 24 x 365 to get hourly annualized total = 96,360 kelvin-hours / annum

Specific heat capacity of air ( at 20 degrees ) is 0.33 w/m3K

So

500 x 0.25 x 96,360 x 0.33 = 3,974,850 w/annum or 3,975 kw/annum.

Lets say one has a 90% efficient boiler
Oil costs ~ 11c/kw = €437
Gas costs ~ 7.5 c/kw = €298


If AT test was 2 then

500 x 0.1 x 96,360 x 0.33 = 1,589,940 w/annum or 1,590 kw/annum.

Lets say one has a 90% efficient boiler
Oil costs ~ 11c/kw = €175
Gas costs ~ 7.5 c/kw = €119

just do it

fclauson wrote: »

This tables shows how much saving over 15 years you could get

target build @.6 ACH €-
target build @ 1 ACH €1,367
target build @ 2 ACH €4,932
target build @ 3 ACH €8,688
target build @ 4 ACH €12,607

sinnerboy wrote: »

Quick and dirty calc for infiltration losses

example

Floor area 200m2.
air change rate (test ) = 5 .
Oil costs ~ 11c/kw = €437


If AT test was 2 then
Oil costs ~ 11c/kw = €175

Apologies fclauson & sinnerboy for chopping but I'm just trying to compare the 2 separate ways at coming at this.

So taking Fclauson's calculations are based on 250m2 over 15 years (open to correction) and taking Sinnerboys figures:
Annual difference in oil = €262
For 250m2 = €327.50
Over 15yrs = €4,912.50

(Fc - have you factored in a 10% in oil in those figures?)

So there is a €5k over 15yrs by bringing your AT down from 5 to 2 for a 250m2 house.

Both approaches show a substantial saving to made from good attention to air tightness!

(All open to correction;))

just do it

BryanF wrote: »

its the hierarchy that matters, building fabric first.. etc

Bryan
Fancy listing the items in order of priority? Could open up a good debate...:D


.

sinnerboy

1 €262.00
2 €288.20
3 €317.02
4 €348.72
5 €383.59
6 €421.95
7 €464.15
8 €510.56
9 €561.62
10 €617.78
11 €679.56
12 €747.52
13 €822.27
14 €904.50
15 €994.94
€8,324.39

That is €262 increasing 10% year on year

Rule of thumb

70 / % rate of increase = approx doubling

So anything increasing at 10% constant will double each 7 years ( roughly )

sinnerboy

just do it wrote: »

Bryan
Fancy listing the items in order of priority? Could open up a good debate...:D

A bit like asking which of your fingers is most useful ( Abondon smutty thoughts and say 3 Hail Marys ) They all act together.






......stop sniggering :rolleyes:

just do it

sinnerboy wrote: »

A bit like asking which of your fingers is most useful ( Abondon smutty thoughts and say 3 Hail Marys ) They all act together.






......stop sniggering :rolleyes:

I'd put quality of workmanship at the top of the list!

just do it

just do it wrote: »

Apologies fclauson & sinnerboy for chopping but I'm just trying to compare the 2 separate ways at coming at this.

So taking Fclauson's calculations are based on 250m2 over 15 years (open to correction) and taking Sinnerboys figures:
Annual difference in oil = €262
For 250m2 = €327.50
Over 15yrs = €4,912.50

(Fc - have you factored in a 10% in oil in those figures?)

So there is a €5k over 15yrs by bringing your AT down from 5 to 2 for a 250m2 house.

Both approaches show a substantial saving to made from good attention to air tightness!

(All open to correction;))

sinnerboy wrote: »

1 €262.00
2 €288.20
3 €317.02
4 €348.72
5 €383.59
6 €421.95
7 €464.15
8 €510.56
9 €561.62
10 €617.78
11 €679.56
12 €747.52
13 €822.27
14 €904.50
15 €994.94
€8,324.39

That is €262 increasing 10% year on year

Rule of thumb

70 / % rate of increase = approx doubling

So anything increasing at 10% constant will double each 7 years ( roughly )

Both methods of calculation are coming up with pretty much the same results! Even if there is no increase in the price of oil, there is still a substantial saving, particularly if you're hoping it will be your family home for the next 30, 40, 50 years

galwaytt

just do it wrote: »

I'd put quality of workmanship at the top of the list!

Exactly. A 'lower performance' product, built well, will out-perform a 'higher performance' one, built poorly.

I heard someone say once that he judged AT to be the arbiter of quality: i.e., how well the building was put together. The lower the number, the better it was - so even if you ignore energy etc, it's still a good yardstick.

No point in having high 'on-paper' u-values for walls, say, if there's gaps all over the place - it still won't 'work'.

fclauson

sinnerboy wrote: »

Quick and dirty calc for infiltration losses

volume x air change rate x delta t x specific heat capacity of air

example

Floor area 200m2. Average Height 2.5m = Volume 500m3

air change rate (test ) = 5 . Divide by 20 for air change at normal pressure = 0.25

Delta t . ( Bear with me )

Take indoor temp at 20 kelvin ( celcius )

Average year round temp in Ireland is 9 degrees so Delta t is 11
x 24 x 365 to get hourly annualized total = 96,360 kelvin-hours / annum

Specific heat capacity of air ( at 20 degrees ) is 0.33 w/m3K

So

500 x 0.25 x 96,360 x 0.33 = 3,974,850 w/annum or 3,975 kw/annum.

Lets say one has a 90% efficient boiler
Oil costs ~ 11c/kw = €437
Gas costs ~ 7.5 c/kw = €298


If AT test was 2 then

500 x 0.1 x 96,360 x 0.33 = 1,589,940 w/annum or 1,590 kw/annum.

Lets say one has a 90% efficient boiler
Oil costs ~ 11c/kw = €175
Gas costs ~ 7.5 c/kw = €119

Simple spread sheet attached to match Sinnerboy''s maths

fclauson

just do it wrote: »

Apologies fclauson & sinnerboy for chopping but I'm just trying to compare the 2 separate ways at coming at this.

So taking Fclauson's calculations are based on 250m2 over 15 years (open to correction) and taking Sinnerboys figures:
Annual difference in oil = €262
For 250m2 = €327.50
Over 15yrs = €4,912.50

(Fc - have you factored in a 10% in oil in those figures?)

So there is a €5k over 15yrs by bringing your AT down from 5 to 2 for a 250m2 house.

Both approaches show a substantial saving to made from good attention to air tightness!

(All open to correction;))

yes about right - an my calc was from the PHPP sheet - with oil starting at 80c per litre and going up 10% per year

sinnerboy

fclauson wrote: »

Simple spread sheet attached to match Sinnerboy''s maths

Saves paper and ink ....

sinnerboy

Just one two things - I would cost electricity @ 17c/kw for heating

http://www.seai.ie/Publications/Statistics_Publications/Fuel_Cost_Comparison/Domestic_Fuel_Costs_Comparison_Apr_2011.pdf

( Avg domestic consumption for is 5000kw/year )

Note the 14% increase in oil since new year. If constant doubling time will at 2016.

.

just do it

fclauson wrote: »

Simple spread sheet attached to match Sinnerboy''s maths

There's a work colleague who has a mug he's very proud of with "I LOVE SPREADSHEETS" on it:D

fclauson

sinnerboy wrote: »

Just one two things - I would cost electricity @ 17c/kw for heating

.

I was assuming some usage of overnight cheap electricity

sinnerboy

To be safe then I'd cost @ 14c/kw. The difficulty with proposing electricity for heating ( assuming a heat pump is used ) is the time lag between the time the "switch on time" and the "user requires heat time".

Quite often specifiers will seek to use a thin screed ( floscreed / beades ) to cut down on the lag time for UFH. If using a dual tarrif meter to reduce running costs in this scenario then what one is doing is shifting the warm up phase from night rate to day rate - and losing the cost advantage. It would be better to use a conventional screed and maybe even up the thickness from 75mm to 100mm . This way you move the warm up period back into the night period.

But even when doing so , in the midst of our long heating season , one will inevitably be demanding energy at day rate.

I can't demonstrate this by calculation ( sorry ) . but it was a heat pump vendor who gave me this heads up about this at an SEAI Energy Show.

galwaytt

sinnerboy wrote: »

To be safe then I'd cost @ 14c/kw. The difficulty with proposing electricity for heating ( assuming a heat pump is used ) is the time lag between the time the "switch on time" and the "user requires heat time".

Quite often specifiers will seek to use a thin screed ( floscreed / beades ) to cut down on the lag time for UFH. If using a dual tarrif meter to reduce running costs in this scenario then what one is doing is shifting the warm up phase from night rate to day rate - and losing the cost advantage. It would be better to use a conventional screed and maybe even up the thickness from 75mm to 100mm . This way you move the warm up period back into the night period.

But even when doing so , in the midst of our long heating season , one will inevitably be demanding energy at day rate.

I can't demonstrate this by calculation ( sorry ) . but it was a heat pump vendor who gave me this heads up about this at an SEAI Energy Show.

Exactly. Irrespective of what technology is in the house, and what tariff you're on, if the system is calling for (power) during the day (off-night) then you can't very well 'deny' it. And when this happens, you end up paying a lot more for your electricity, as the day-rate is much higher. For this reason I think you should predicate your costs on the higher rate, not the lower. If it works out at that higher, you're elected if the end-cost turns out ot be the lower - but not the other way around..........

I know of a couple of house with ASHP that have fallen into this trap.

sinnerboy

sinnerboy wrote: »

Which also underscores the foolishness of undertaking the biggest financial burden of your life without seeking professional guidance. The internet is no substitute.

Are architects qualified for this ? Or do you need to see air tightness/insulation experts for this design ?

just do it

Deleted User wrote: »

Are architects qualified for this ? Or do you need to see air tightness/insulation experts for this design ?

Some are. Use of PHPP is still new here but gaining momentum. If you have recommended architects in mind give them a ring and you'll quickly find out! Others will work with an energy consultant who uses PHPP. Designing the layout and look of a build is completely different to deciding what construction type to use. Architects are trained in the former.