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Office case study cibse AwArd winner
The design of the offices
incorporated the idea of
keeping the supply of fresh
air to a minimum
Predicted vs actual energy use
John Williamson’s prediction
for energy consumption was
unnecessarily high. Two years of
monitoring has shown the total
operational energy consumption
to be just 80k Wh/sq m/yr. He
says that this is probably because
computer use has been lower than
expected.
Monitoring showed that internal
summer temperatures did reach
26C maximum in the first summer.
However, the reason for this was
found to be due to an external
38
ventilation fans. His premise was that the
scheme would use less energy and the
building would be more comfortable if
the supply of air was kept to the absolute
minimum. This small amount of fresh
air could then be cooled, perhaps using a
small heat pump, before it is supplied. In
summer, this solution would keep heat
out of the building during the day and
enable the ventilation fans to be turned
off at night. He is currently applying for
research funding to test his premise on part
of the building’s ventilation system to find
out whether this would be a more energy
efficient ventilation solution for future
Passivhaus offices.
sensor, damaged by a football,
shutting down the night purge
ventilation too soon. For heating,
through two of the coldest winters
on record, temperatures varied
between 20C and 22C, depending
on the occupier’s control of the
radiators using thermostatic
radiator valves.
However, when the building is
fully occupied the heat gains are
sufficient to keep the radiators
turned off which means the boiler
is only used for a short time on
calculation Methodolgy sq m kwh kwh/m 2 /a kwh/
Co 2 m 2 /a
very cold mornings. As a result of
this, and because the solar gains
were higher than expected, the
building’s space heating load of
14.8 kWh/sq m is also slightly
lower than the 15 kWh/sq m/
yr predicted. To put this into
perspective, the building’s gas bill
was £130 for a recent 12-month
period.
The photovoltaic panels have
also performed better than
predicted. ‘We installed the PVs
to show how a small area of a
The ventilation design was further
complicated by Powys County Council’s
last-minute decision to add a computer
server room to the scheme, which added an
additional 720 W of heat. The council also
decided to stick with its existing computer
framework supplier rather than purchase
ultra-low energy machines.
‘Suddenly, IT energy use rocketed,’
Williamson laments. What’s more, the
increased ventilation needed to offset the
additional heat gains pushed the scheme’s
annual energy consumption up from 112
kWh/sq m/yr to 184 kWh/sq m/yr, far
above the 120 kWh/sq m/yr allowed by
Passivhaus, jeopardising the building’s
certification.
Following these changes, Williamson
was forced to refine the design at the last
minute. As a result, a brise-soleil was added
to the ground-floor glazing on the southern
elevation. Extensive daylight control was
added to the T5 lighting to push its energy
consumption below 10W/m2. Mechanical
timers were installed to shut down all
electrical sockets at night to eliminate
standby losses.
Movement detectors were added to the
MVHR systems serving the computer
rooms to enable the lights to be turned off
and the ventilation turned to ‘low’ when
the rooms are unoccupied. These units
will run on medium speed when the room
is in use; the high setting will only kick in
when temperatures exceed the Passivhaus
low maintenance, reliable
technology can make a big
contribution to a low energy
building,’ says Williamson. The
panels have produced 5,987 kWh/
yr, which equates to about 20% of
building’s needs. Unfortunately,
because the PV installation was
grant-funded, Powys County
Council cannot claim a feedin
tariff; had it done so, says
Williamson, the tariff would have
been ‘more or less equivalent to
the gas and electricity bills’.
SPaCE HEatIng total oPEratIonal EnErgy total PV gEnEratIon (7kw array) total
fuEl
CarBon
Gas 08/10/09 - 08/10/10 (0.194kg/cO /kwh) 2 electricity 08/10/09 - 08/10/10 (0.568kg/co /kwh) 2 CoSt
08/10/09 - 08/10/10 EmISSIonS
£/yr kwh kwh/m 2 /a kwh/
Co 2 m 2 /a
£/yr £ kwh/a kwh/
Co 2 m 2 /a
approx fit
income £
Passivhaus 335 Predicted 5,025 15.0 2.9 48,240 144 81.8 5250, 8.9 1,895.00 75.8
Canolfan Hyddgen 335 Actual 4,973 14.8 2.9 131.1 26,860 80 45.5 2409.82 2540.93 6,493 11.0 2,600.00 37.4
Canolfan Hyddgen Part l2 391 Actual 4,973 12.7 2.5 131.1 26,860 69 39.0 2409.82 2540.93 6,493 9.4 2,600.00 32.1
Bldg reg notional Part l2 391 Predicted 17,986 46 8.9 15,640 40 25.2 5,250 7.1 1,895 127.1
kwh/
Co 2 m 2 /a
CIBSE Journal April 2011 www.cibsejournal.com