Technologies for sustainable Built Environments
Zero Carbon Homes: Analysis of space heating demand
and thermal comfort
Robert Burzynski | Runming Yao | Victor M. Becerra | Martin Crane
Summary and lessons learned
Space heating
Thermal comfort
To achieve ambitious targets in CO2 missions reduction the UK
government tightens the requirements imposed on housing
developers to build new houses to the net zero carbon
Annual consumption
Overall experience
During the first and third year of occupation the houses
standard from 2016. This means that the houses should use
very limited amount of heat and electricity and still be able to
deliver acceptable, comfortable conditions to their residents.
consumed 340% and in the second 390% of the SAP 2005
calculated value. Electricity consumption and the number of
occupants were similar to the ones estimated in SAP therefore these
factors were unlikely to be the cause of the increased consumption.
In general the perception of the thermal comfort varied
between the residents. Most residents were generally satisfied
with overall indoor temperature and only one household used
auxiliary heating on semi regiular basis . The residents were
generally willing to adapt their behavior to the circumstances.
To meet those requirements a few companies started
designing and constructing low energy houses utilising
different technologies and energy solutions.
Unfortunately, few of them conducts a post occupancy
evaluation to verify real performance of their buildings.
The problem
There is growing but still limited evidence, especially from
residential sector, of a gap between design and real
performance [1-2]. According to data from the CarbonBuzz [3]
on average buildings consume between 1.5 and 2.5 times
predicted values. Therefore, there is an urgent need to
measure and analyse real energy demands of houses and
propose possible improvements for underperforming areas.
• Locating MVHR within the builing envelpe would cause
noticable reduction of space heating consumpiton and
improvement in thermal comfort.
• Adding radiators with TRVs in bedrooms would give
more control of the local temperatures and remove any
unwanted temperature differences between rooms .
Annual Space Heatng (kWh)
Consumption
Introduction
3500
• The residents undertook a combination of adaptive
Overall
temperature
3000
actions to mitigate the issues with their tharmal
3
2500
2
Humidity
2000
1
0
Temperature
fluctuation
comfort e.g. wearing more clothes, setting programmer
to keep constant temperature, temporally using
-1
1500
-2
auxiliary heaters.
-3
1000
Draughts
500
Temperature rise
dynamics
• Proper commissioning / balancing of the MVHR system
0
1BR
1BR
2BR End 2BR Mid
3BR Det
3BR Det
3BR End
3BR End 3BR Mid
Houses
SAP 2005
Measured
Satisfaction Levels
+3 - Very satisfied
0 - Neutral
-3 - Very dissatisfied
3BR Det- 3 Bedroom Detached House
Overall
ventilation
improved the system performance (both in terms of
Easiness in using
programmer
energy efficiency and thermal comfort) but this proved
to be beyond the abilities of a non specialist M&E
contractor.
Figure 2. Overall satisfaction levels with space heating and mechanical ventilation system.
Figure 1. Comparison of annual space heating consumption calculated with SAP 2005 and measured
from September 2011 to April 2012.
• SAP methodology should take into account significant
Analysis of data from eight occupied Zero Carbon Houses in
Slough has been used to investigate this issue. General analysis
show that the measured electricity consumption is very closed
Possible cause of high consumption
Problematic areas
heat losses from the ventilation system unless the
Indoor temperature – The average living room temperature
system is entirely located within the building envelpe.
to the predicted level. The energy used for domestic hot water
preparation was about 38% lower than the design estimation.
However, the energy used for space heating was about 3 .5
times higher than the design estimation. Additionally the
thermal comfort of residents was partly compromised.
was about 1°C higher than assumed in SAP 2005.
Room temperatures – The residents reported dissatisfaction with
the temperature difference between living room and bedrooms
which varied among houses from 1°C to 2 °C .
Characteristic of the houses
Airtightness - This was higher than design and varying from 2.1
m3/m2h to 3.9 m3/m2h with one outsider reaching 8.1 m3/m2h.
Limited temperature control – The heating system and
controls installed in the houses do not allow the residents to
independently adjust the temperature in bedrooms. The
response time to change in the temperature setting on the
programmer was found rather long.
Envelope U-values – Although not tested with co-heating test
the thermal imaging showed increased heat losses through
some parts of the building envelope.
0.8W/m2K.
and windows
To reduce ventilation
heat loss the houses were designed to achieve airtightness of
up to 2 m3/m2h. With high airtightness level the houses had to
be equipped with a mechanical ventilation system with heat
recovery (MVHR) . The heat for a space heating is provided from
local renewable energy plant via district heating network. In
each house there is only one main radiator in a living room, a
towel rail in a bathroom and a heater battery in the ventilation
system.
Drafts – The residents reported unpleasant cold draft from air
supply grills especially when the outdoor temperature was low.
the ductwork is located in the unheated loft which is outside of
the insulated envelope. For the average temperature
25.0
of 0°C and loft air temperature of 5°C the
24.0
heat loss from the ductwork, heater battery
23.0
and the MVHR unit was estimated to be
22.0
about 300W. This is 24% of additional heat
21.0
consumption if compared to the SAP 2005
20.0
estimated whole house heat loss of 1260 W.
Additional duct air leakage, clogged air intake
filters and ice forming in the heat exchanger
reduced the heat recovery rate thus adding to
overall heat demand of the buildings.
Living room temperature (°C)
0.12 W/m2K
MVHR noise – Most residents
reported noise nuisance from the
MVHR that was located just above
the main bedrroms.
18.0
1BR
2BR End 2BR Mid 3BR Det 3BR Det 3BR End 3BR End 3BR Mid
Show
Houses
Measured
performance in use, 2. Energy performance of the probe buildings’, Building
Research and Information, 29 (2) (2001).
2. Carbon Trust, Closing the gap Lessons learned on realising the potential of low
3. CarbonBuzz, www.carbonbuzz.org, Accessed on 13/06/2013
Acknowledgements
19.0
1BR
1. W. Bordass, R. Cohen, M. Standeven, A. Leaman, ‘Assessing building
carbon building design, CTG047 (2011)
MVHR system design , installation and operation – The unit and
The housing development consists of eight houses and two
flats. The construction is characterised by very high levels of
insulation with U-value for floors and roof of 0.10 W/m2K, walls
References
Set on SH programmer
SAP 2005
Measured Average
Figure 1. The living room temperatures assumed in SAP 2005 and measured in different houses.
The authors would like to thank EPSRC and SSE for funding this research project
Contact information
•
TSBE, University of Reading, Whiteknights, JJ Thomson Building, PO Box 220, Reading RG6 6AF.
•
Email: r.burzynski@pgr.reading.ac.uk
|
www.reading.ac.uk/tsbe