Why is Thermal mass useful

From;
Thermal mass explained from Australia
"Why is thermal mass important?
When used correctly, materials with high thermal mass can significantly increase comfort and reduce energy use in your home.
Thermal mass acts as a thermal battery to moderate internal temperatures by averaging out day−night (diurnal) extremes.
In winter, thermal mass can absorb heat during the day from direct sunlight.
It re-radiates this warmth back into the home throughout the night.
In summer, thermal mass can be used to keep the home cool. If the sun is blocked from reaching the mass (for example, with shading), the mass will instead absorb warmth from inside the home.
You can then allow cool breezes and convection currents to pass over the thermal mass overnight to draw out the stored energy.
Conversely, poor use of thermal mass can reduce comfort and increase energy use.
Inappropriate thermal mass can absorb all the heat you produce on a winter night or radiate heat to you all night as you try to sleep during a summer heatwave. "
Also
"Thermal mass is the ability of a material to absorb, store and release heat.
Thermal lag is the rate at which a material releases stored heat.
For most common building materials, the higher the thermal mass, the longer the thermal lag.
"

From the link above:
> Thermal lag is the rate at which a material releases stored heat

I think that should say *inversely* related.  Since more lag yields a slower heat rate. And less lag yields a faster heat rate.  

> For most common building materials, the higher the thermal mass, the longer the thermal lag

I’m skeptical of that. When I calculate the thermal lag of a material, I find it’s a function of both heat capacity and insulation. https://en.m.wikipedia.org/wiki/Thermal_lag

> Materials with high thermal mass and long lag times are often simply referred to as ‘thermal mass’. These are typically heavyweight construction materials like concrete, brick and stone. Materials with low thermal mass are typically lightweight construction materials, like timber frames.

Except, timber isn’t lighter weight than aerated concrete.  They’re both about 600 kg/m^3. When I calculate the lag time of timber, it’s actually higher than solid concrete and stone.

Since I have a concrete slab foundation, I have learned that the slab is a thermal mass that helps keeps my house warm in the winter and cool in the summer.

Unheated rooms stay warm in the winter.

Currently, my part of Texas is experiencing triple-digit temps.  The cat understands about this thermal mass.  She comes into the house to lie on the concrete floor to cool off every now and then.

Mike, can you show me the figures about timber and solid concrtye please?

Anne, it is a misunderstood topic.
But if more understood about it they would perhaps;
- not carpet concrete or tiles that gets the sun.
- use more
- have some thermal mass in sun soaked interior walls

John C Daley wrote:Anne, it is a misunderstood topic.
But if more understood about it they would perhaps;
- not carpet concrete or tiles that gets the sun.
- use more
- have some thermal mass in sun soaked interior walls

Why is this a misunderstood Topic?

I have no carpet only concrete floors.

I have no sun inside my home or sun soaked interior walls as it is too hot here.

Use More? my house is already built I don't plan to add more concrete??

What is so hard about this if my cat can understand the benefits?

https://en.wikipedia.org/wiki/Thermal_mass

Anne Miller wrote:Since I have a concrete slab foundation, I have learned that the slab is a thermal mass that helps keeps my house warm in the winter and cool in the summer.

Except when there's no thermal break between that slab and the concrete knee-wall, and no insulation on the outside of the knee wall, and you live in a damp climate with no thermal gain on that knee wall.

Then it's just a nuisance... bad design which would cost more to fix than the building is worth.