Online Seminar Questions - Thermal Mass
To help you understand the Code for Sustainable Homes, The Concrete Centre and our technical team have produced answers to the questions we have recieved from our online seminar.
This section will cover all questions relating to thermal mass.
1. "I am curious to know your views on the fact that as the world temperature increases and seasons are changing do you think that the off peak seasons will create too high a temperature and thus make thermal mass idea inappropriate as the heat will be too strong?"
Response - Andrew Minson, The Concrete Centre: "Thermal mass is of benefit in buildings as a heat sink/heat recovery on a time scale of days - typically one day or days. In the summer, the nighttime temperature must be low enough to purge the heat from the thermal mass. If there is a heat wave over a series of days and nights, the thermal mass benefit decreases, as it is less able to absorb heat during the hot period. The thickness of thermal mass you have determines how long a heat wave you can last. In the winter, if there is no mechanical heating, then the same argument applies. Thermal mass in housing is not storing summer heat and re-radiating it in the winter. The time scale is days not six months."
2. "What was the mass of heavy weight house per m sq?"
Response - Andrew Minson, The Concrete Centre: "The heavyweight house was a fair-faced heavyweight concrete block for external walls (inner leaf) and partitions, precast concrete floors for ground and first floor ceilings (fair-faced) and solid ground floor slab. Floor finishes were hard. Structurally the additional weight of the structure was small. It did not affect the foundations."
3. "Andrew showed the climate change/thermal mass study based on a starter home. Would we see similar results for a larger building, such as a concrete/masonry apartment building?"
Response - Andrew Minson, The Concrete Centre: "We would expect to see similar results for other housing, including apartments. For apartments a difficulty can be in the planning to have all dwellings facing approximately southwards."
4. " Does the MVHR meant that energy demands are higher in the property and if so by how much are the energy and CO2 figures affected?"
Response - Andrew Minson, The Concrete Centre: " MVHR - Mechanical ventilation heat recovery. The studies do not include MVHR in any of the houses. MVHR systems are likely to become more widely used and are most efficient when used in conjunction with thermal mass. MVHR describes a system where fresh air is preheated by exhaust air."
5. "For the future, are we generally looking to increase heat gain or decrease heat gain?"
Response - Andrew Minson, The Concrete Centre: "Heat gain in UK buildings is predicted to increase at all times of the year. Therefore, in winter we will expect to have to heat our houses less. With passive solar design and thermal mass we can reduce our heating bills even more. In the summer, we will have more periods of hot days when we will benefit from thermal mass keeping us cool. Without thermal mass, overheating and subsequent installation of air conditioning will be more common."
6. " What is the optimum amount of thermal mass in a house, and what is its relationship with size of south facing windows?"
Response - Andrew Minson, The Concrete Centre: "There is increasing benefit to be gained from having more thermal mass in a house, in the reasonable designs likely to be built. Therefore, there is not an optimum - the more the better. By reasonable: we have looked at concrete slabs and walls with the thickness needed for fire, acoustics and structural performance and found that all of this thermal mass is of benefit."
7. "Is a cement particleboard a viable but better thermal mass-providing alternative to plasterboard?"
Response - Andrew Minson, The Concrete Centre: "The thickness of boarding is an order of magnitude (approximately ten times) less than the amount of thermal mass needed. If boarding is on a thermally massive substrate, i.e. a concrete block, the conductivity of the board is the most significance property."
8. "Does plasterboard on dabs not reduce the benefits of thermal mass? Would wet plaster not be better?"
Response - Andrew Minson, The Concrete Centre: "Wet plaster is much better and we have this as an option in our study. It is in our 'heavyweight house'. Wet plaster provides better thermal linkage to the thermally massive walls. The same applies with floor finishes: tiles are better than carpet; and ceilings: avoid suspended ceilings. Internal acoustics must consequently be considered, but there is a design balance to be struck to get the energy efficiency required and acoustic performance."
9. "When do you anticipate overheating being covered by Building Regulations?"
Response - Andrew Minson, The Concrete Centre: "Overheating is currently loosely covered in the regulations. It was added with the last amendment. There is every indication that it will be more rigorously covered in the next round of changes."
10. "The full heavy weight house is at Hockerton 2.5 t per m² . At this mass heating systems can be left out. How can we convince people that zero heating is the way forward?"
Response - Andrew Minson, The Concrete Centre: "The Code for Sustainable Homes will start convincing people that zero heating is the way forward."
11. "How much south facing glazing in relation to optimum heating of thermal mass?"
Response - Andrew Minson, The Concrete Centre: "For passive solar design with normal double glazing, up to 50% of the southern façade can usefully be window, this equates to about 25% of the floor area in a typical dwelling. For more information see p5 Thermal Mass for Housing."
12. "Currently, there are phase changing materials, which provide thermal mass and avoid pollution -in comparison to concrete. Could you let me know what advantages concrete has against these phase changing materials?"
Response - Andrew Minson, The Concrete Centre: "Phase change materials are yet to be developed to overcome disadvantages related to: prone to damage, expensive, contain kerosene, how long do they function as intended, etc. The concept though is very strong."
13. Does increased thermal mass mean greater non-repeating thermal bridging values?
Response - Andrew Minson, The Concrete Centre: "No. Thermal mass work must be inside the insulation. By definition then, it is not cold bridging. There are construction details for heavyweight construction to avoid cold bridging."
14. "If concrete produces more carbon dioxide in the first 11 years compared to light frame, and only benefits are after 11 years. Would a different way of thinks about replacing houses every 10 years be more energy efficient and keeping up with the light designs and recycle light steel homes instead of building for 100 year?"
Response - Andrew Minson, The Concrete Centre: "After a ten-year life, the majority of the 40 tonnes of CO2 of a house has been caused by building it - no matter what construction material was used. Therefore, replacing houses every ten years will cause much more significant impact. After twenty years the CO2 emissions of build and operation is approximately 60 tonnes. If the house has been knocked down after ten years and replaced, the overall impact would have been 2 x 40 tonnes = 80 tonnes."
15. "With Durox thin bed joint system and the insulation on the outside is there a significant reduction on thermal mass over say a dense concrete block?"
Response - Colin Marshall, Tarmac Topblock: "The study of the benefits of thermal mass in housing referred to in the presentation by Andrew Minson of The Concrete Centre, did not specifically include aircrete products but was based on lightweight (timber frame), medium weight (medium density blocks), medium-heavy weight (as before but with concrete first floors) and heavy weight (dense block and concrete first floors) constructions.Whilst aircrete has a relatively low density (460-730 kg/³m), it still provides a very useful amount of thermal mass. When finished with plaster, an admittance value of 2.86W/m²K is achieved. This is around three times higher than a timber frame wall with plasterboard, which has an admittance of 0.85W/m²K. More importantly, it has a very similar admittance value to medium dense aggregate blocks (2.95W/m²K) which the study showed performed similarly to a dense block construction. In short, the use of Durox will still provide significant benefits on a par with more heavier forms construction whilst, in addition, providing inherent thermal insulation benefits."
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