How fast does your house cool down ?

RelievedSheff

Deleted_User said:

RelievedSheff said:

Deleted_User said:

jacko220 said:

Depends upon two things, first of all the Construction and what is known as the U-value of the construction measured in Watts/,^2/Deg C, that is how many watts the construction will loose per square metre of area per Degree Centigrade of difference between inside and outside , the Deg K that is sometimes used is Degree Kelvin the difference in Deg K and Deg C is the same it starts from a difference place. The next is how leaky the house is due to air leaking from the house. I lectured in this for nearly 40 years, if anybody wants to ask questions please feel free. It also depends on the Admittance value of the structure, that is how much heat is stored by the insides of a building, If you wish to ask questions please feel free.

And another question that is baffling me. My street has 14 x 20 year old bungalows with concrete tile roofs. Some people have added to the loft insulation to get it up to standard. Others haven't. ALL houses have thick frost on them when temps are below zero overnight and NONE thaw out faster than others. 

That's an easy one to answer.

They are constructed with a "cold roof space". I.E the insulation is laid over the ceiling joists so that the roof space is left unheated.

Doesn't matter how much insulation they put up there, it will still be a cold space.

So the warm air escapes via gaps in the eves - which you don't want to block? Makes sense. Cheers. 

No. The warm air, in theory, doesn't make it into the roof space at all.

Sea_Shell

RelievedSheff said:

Deleted_User said:

RelievedSheff said:

Deleted_User said:

jacko220 said:

Depends upon two things, first of all the Construction and what is known as the U-value of the construction measured in Watts/,^2/Deg C, that is how many watts the construction will loose per square metre of area per Degree Centigrade of difference between inside and outside , the Deg K that is sometimes used is Degree Kelvin the difference in Deg K and Deg C is the same it starts from a difference place. The next is how leaky the house is due to air leaking from the house. I lectured in this for nearly 40 years, if anybody wants to ask questions please feel free. It also depends on the Admittance value of the structure, that is how much heat is stored by the insides of a building, If you wish to ask questions please feel free.

And another question that is baffling me. My street has 14 x 20 year old bungalows with concrete tile roofs. Some people have added to the loft insulation to get it up to standard. Others haven't. ALL houses have thick frost on them when temps are below zero overnight and NONE thaw out faster than others. 

That's an easy one to answer.

They are constructed with a "cold roof space". I.E the insulation is laid over the ceiling joists so that the roof space is left unheated.

Doesn't matter how much insulation they put up there, it will still be a cold space.

So the warm air escapes via gaps in the eves - which you don't want to block? Makes sense. Cheers. 

No. The warm air, in theory, doesn't make it into the roof space at all.

But does the escape of any heat into the loft depends on the level of insulation.    Surely more insulation means less heat can escape?

Green_Eye

Ballymoney said:

FreeBear said:

Last night, with the outside temperature down to 2°C, it took five hours to drop 1°C in the hallway (where the CH thermostat is located) from 18°C.

That’s incredibly impressive.

We currently switch the heating off at 22:00 at 19c and by 08:00 today the temp in the hallway had dropped to 13.5c. It was -2c here though. Took a good 1hr 45 to get the house up to 18c. 

130kwh of gas used in last 24hrs.

May I ask, what was the total cost and how long would you have had the heater on for to get it up to that usage?

jacko220

Deleted_User said:

jacko220 said:

Depends upon two things, first of all the Construction and what is known as the U-value of the construction measured in Watts/,^2/Deg C, that is how many watts the construction will loose per square metre of area per Degree Centigrade of difference between inside and outside , the Deg K that is sometimes used is Degree Kelvin the difference in Deg K and Deg C is the same it starts from a difference place. The next is how leaky the house is due to air leaking from the house. I lectured in this for nearly 40 years, if anybody wants to ask questions please feel free. It also depends on the Admittance value of the structure, that is how much heat is stored by the insides of a building, If you wish to ask questions please feel free.

I'll take you up on that offer!!

OK - so even a thermos flask will lose heat quickly in cold weather. I have a high performance flask and in milder weather boiling water put in the night before can be used to make a cuppa in the morning. But in this cold snap the water is only warm by morning.

So without a heat source houses with state of the art insulation will lose heat overnight.

If I put a tea cozy over my flask (analogy with topping up loft insulation) it probably slows down heat loss in a measurable way, but I still have luke warm water in the morning.

So I guess my questions are focussed around diminishing return on investment. If you have a house with decent insulation (lets say 20 year old standards) how would YOU go about working out the point at which further insulation is going to cost you more than you'll save in it's lifetime? If 90% of the year your insulation is performing well how much is it worth spending to improve it for 10%? Often it will be much cheaper just to accept the higher energy costs in cold snaps.

And another question that is baffling me. My street has 14 x 20 year old bungalows with concrete tile roofs. Some people have added to the loft insulation to get it up to standard. Others haven't. ALL houses have thick frost on them when temps are below zero overnight and NONE thaw out faster than others. 

So observation 1 is that this little bit of extra insulation isn't making enough difference to change the rate at which ice on the roof thaws?

Here's the puzzling bit - next door neighbour had an extension build in the summer. He commented on how thick the insulation was in the loft - he was amazed at the difference between old and current standards. In all other ways roof construction is identical to the original houses - watched it being built. Yet in this bitterly cold weather, every house has a thick coating of frost on the roofs - except his new extension. It frosts up overnight but thaws quickly in the morning. How can that even be possible?

Think of it this way water will find its own level, the level of water is the temperature, as you say temperature drops more quickly in colder weather. No matter what you are going to do heat will flow from hot to cold or cold to hot that is a matter of semantics. 

I have been asked to write in paragraphs, so here goes. The U-value of construction is determined from the thermal conductivity or k or lambda value of  a material, generally the less dense a material the lower the thermal conductivity, so hence mineral wool is a better insulator than solid brick and "breeze", they are not breeze but aircrete blocks, like an aero bar are better than solid bricks, the density of bricks if about 1700 kg/m^3 and that of modern aircrete blocks 440 kg/m^3. 

The reciprocal is 1/k which gives the resistivity and multiplied by the thickness gives the Resistance, the U-value in turn is 1/ Sigma (Sum of ) Resistances, so you are correct it is diminishing returns, ie adding 50 mm to 100 mm is better than adding 50 mm to 150mm. 

I do hope this helps, please feel free to ask any questions, for optimum levels of insulation look at Building Research Establishment Energy Conservation Unit (BRECSU). Please do not block up the vents in your roofspace it will cause condensation, hence the Building Regulations require air gaps at eaves level or other means to create a cross flow of air which will remove the moisture, the air in the roof space is colder and the Saturated Vapour Pressure of the air the temp at which it condenses is lower, condensation and mould do to timber what it did to that little boy the other day.

Sorry for the ramble but I still have not dealt with heat loss due to ventilation and condensation, heating and condensation are interlinked.

Sorry to be a geek. 

Ballymoney

Green_Eye said:

May I ask, what was the total cost and how long would you have had the heater on for to get it up to that usage?

Cost is about £14 for gas and that covered the heating being on from 08:00 to 22:00 at 19c and 2 showers. 4 bed 1950’s detached up north. 
 

Absolutely mental figures when you think about it…which is why I try to no longer do.

grn99

3 degrees lost over 5 hrs here 18 down to 15. Outside temp appears to have been -3

brewerdave

How fast does it cool down ? Today's Q should be how long before it gets warm enuf !!!

jacko220

Energy in buildings: 2.4.1 Calculating the total heat loss of a house - OpenLearn - Open University

Would suggest this as this is probably better than I could explain, but I will be willing to answer questions that come up.

diystarter7

RelievedSheff said:

Deleted_User said:

RelievedSheff said:

Deleted_User said:

jacko220 said:

Depends upon two things, first of all the Construction and what is known as the U-value of the construction measured in Watts/,^2/Deg C, that is how many watts the construction will loose per square metre of area per Degree Centigrade of difference between inside and outside , the Deg K that is sometimes used is Degree Kelvin the difference in Deg K and Deg C is the same it starts from a difference place. The next is how leaky the house is due to air leaking from the house. I lectured in this for nearly 40 years, if anybody wants to ask questions please feel free. It also depends on the Admittance value of the structure, that is how much heat is stored by the insides of a building, If you wish to ask questions please feel free.

And another question that is baffling me. My street has 14 x 20 year old bungalows with concrete tile roofs. Some people have added to the loft insulation to get it up to standard. Others haven't. ALL houses have thick frost on them when temps are below zero overnight and NONE thaw out faster than others. 

That's an easy one to answer.

They are constructed with a "cold roof space". I.E the insulation is laid over the ceiling joists so that the roof space is left unheated.

Doesn't matter how much insulation they put up there, it will still be a cold space.

So the warm air escapes via gaps in the eves - which you don't want to block? Makes sense. Cheers. 

No. The warm air, in theory, doesn't make it into the roof space at all.

Hi

With respect, when heat rises as it does, no matter how much insulation there is in the roof, some will escape and most of it will become worthless as we are not 9 foot tall people.

There is often a mass of heat within 9 inches or so to the ceiling. This is why people put ceiling fans to draw down the warm air.

Thanks

FreeBear

brewerdave said:

How fast does it cool down ? Today's Q should be how long before it gets warm enuf !!!

Heating kicked in for an hour this morning to go from 17.2°C to 18.4°C - Not too shabby in my opinion.