Peder Vejsig Pedersen Director, M.sc.
Cenergia Energy Consultants
Herlev Hovedgade 195, st., 2730 Herlev, Denmark
Phone: +45 44 66 00 99, fax: +45 44 66 01 36, e-mail: pvp@cenergia.dk, www.cenergia.dk
Abstract
The first Danish passive house building project, Rønnebækhave II in Næstved approximately 100 km south of Copenhagen, was finished in February 2006 [1].
The project included a small two storey housing block with 8 apartments.
Builder was the Danish housing association Domea, and Cenergia Energy Consultants was responsible for the overall energy design which included use of a small ground coupled heat pump and use of solar DHW heating, as well as use of 5 kWp roof integrated PV modules which on a yearly basis should be able to cover the electricity use for the heat pump.
Monitoring of the energy use in the dwellings since the beginning 2007 has confirmed a low energy use in accordance with what was expected based on calculations.
The same concept with use of a solar energy roof to match the yearly energy use for operation was used in the SOLTAG project where a CO2 neutral rooftop apartment was developed and exhibited in Copenhagen from the summer 2005 in a co-operation between the Velux company, Kuben Urban Renewal Denmark, Rubow
Architects and Cenergia Energy Consultants, here according to the Danish low energy class 1 standard, (see also www.soltag.net).
And it has now been decided to realise a SOLTAG passive house project with 24 dwellings in Roskilde, about 35 km west of Copenhagen, based on this experience.
1. Rønnebækhave II in Næstved, the first passive housing project in Denmark
The Danish passive house project Rønnebækhave II in Næstved comprises a small housing block with 8 apartments realised according to the German passive house principles (fig. 1.1.).
The project was realised with support from the EU-Resurgence programme (www.resurgence.info) and it was connected to the “Builders for Sustainability” co-operation connected to the Danish Agency for Commerce and Housing.
Builder was the Danish housing association Domea with Suenson Architects as architect and with civil engineer Peder Vejsig Pedersen from Cenergia as initiator and responsible for the energy design. Erection of the passive housing project in Rønnebækhave II in Næstved was finished by February 2006.
To be able to live up to the German room heating demand which should not exceed 15 kWh/m², year it was necessary to purchase low energy windows from Germany with a documented U-value of 0.8 W/m² °C
(manufacture Haußler), and an individual only 26 cm thick heat recovery unit R200, from the Danish ventilation company EcoVent, (see fig. 1.2.) was placed in a small technical room to enable a “dry” heat recovery
efficiency of 85 % together with a very low electricity use.
EcoVent utilises a Danish produced air to air heat exchanger which clearly has a better performance than imported HRV heat exchangers which have “dry” heat recovery efficiencies around 72 – 75 % measured at the Technological Institute in Denmark except a Dutch plastic heat exchanger which is 82 % efficient but have a too high electricity use for the fans.
For two of the apartments in Rønnebækhave II ventilation air is preheated in the ground.
The apartments utilise a 28 m² shared solar DHW system from Arcon Solar Heating and individual 240 litre DHW tanks. Besides is used a ground coupled shared heat pump from IVT/Bosch in combination with air heating and floor heating. This is matched by PV electricity from a 5 kWp PV system in the roof on a yearly basis. (Gaia Solar manufacturer), so a CO2 neutral design is obtained.
In fig. 1.3. is illustrated the energy frame value for the project. To this can be added that with a calculated energy use for heating and DHW of 23 kWh/m², year only 23/3.5 = 6.5 kWh/m², year will be needed of
electricity for the heat pump with a COP of 3.5. This is the same as the yearly PV production of the PV-modules which is 4250 kWh or 6.6 kWh/m², year.
The experiences with the passive housing project in Næstved has been very good, and here it can be mentioned that especially the balanced HRV systems have been very popular with the tenants where actually two families claim that they have avoided asthmatic symptoms since moving into the apartments.
Due to the limited knowledge concerning passive houses in Denmark, and the general policy concerning energy, at the time of erection it was very difficult to get the project financed and it was also difficult to get funding for monitoring and follow-up. However, it has been possible to realise monitoring since the spring of 2007 where also an extra electricity meter was installed for the heat pump so it was possible to document the actual COP value. The measurements document that it has been possible to obtain results very near to what was expected from calculations with an energy use for heating and DHW near 20-25 kWh/m², year.
Concerning practical operation experiences they have overall been good although there was a problem with a too simple floor heating control which had to be replaced to include temperature monitoring of the floor as basis of a good control.
Besides a problem of missing over temperature control of the solar DHW systems have also been mended.
Fig. 1.1.
50 m² PV-modules in Rønnebækhave II is mounted in the roof facing south in connection to a solar collector area of 28 m².
Fig. 1.2.
Heat recovery unit from EcoVent placed in a small technique room in the dwell-ing.
Energiramme for Passiv Hus boliger i Rønnebækhave II i Næstved sammenlignet med gamle og nye energiregler i bygningsreglementet samt lavenergiklasse 1 og 2.
15 11 11 11 11 11
Energy frame for Passive House dwellings in Rønnebækhave II in Næstved. Here compared to low energy class 2 and 1 inclusive a passive house standard.
2. The SOLTAG prefabricated CO
2neutral rooftop dwelling
A prototype of a new CO2 neutral rooftop dwelling, which was build according to the new Danish low energy class 1 standard, was exhibited at Ørestaden in Copenhagen from August 2005 until the spring 2006 (see fig.
(2.1))
.The prototype development has been supported by the EU-Demohouse project, The Copenhagen Urban Ecology Fund, The Danish Energy Agency and Elkraft-PSO together with a group of sponsors lead by the Velux
company from Denmark. Co-ordination of the project has been facilitated by Cenergia and Kuben Urban Renewal Denmark, who together with Velux and Rubow Architects have developed the prototype housing unit.
The innovative solar roof with air solar collector and PV-panels has been made by Roofing.dk/Ruukki and Danish Solar Energy, while the innovative heating and ventilation system has been made by Gilleje Cooling&Energy together with EcoVent.
The prefabricated rooftop dwelling was manufactured by the Danish company Jytas. (See also www.soltag.net)[5.6].
Fig. 2.1.
Prefabricated SOLTAG CO2 neutral rooftop dwelling exhibited in Ørestad, Copenhagen from August 2005 till the spring 2006. It is now situated at Velux headquarters in Hørsholm.
CO2 neutral roof top apartment minimum demands (year 2015 target ). Same quality
as roof top apartment w ith 0.5 kWp PV panels.
(equal to 3.5 m² crystaline PV modules)
New low energy standard 1 calculated as electricity use by a factor of 2,5
Yearly electricity production from 2kWp PV panels to the south (equal to 17.5 m² crystaline PV modules) is in balance w ith low energy standard 1.
kWh/m² 48 kWh/m²
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Table 2.1.
Energy balance of SOLTAG CO2 neutral rooftop apartment.
The CO2 neutral rooftop dwelling was designed according to an
“Energy Quality Design” philosophy: 6 steps to reduce energy consumption 1. Prefabricated constructions without cold bridges and with a good airtightness.
(Better than 0.6 l/s,m2 as natural ventilation rate)
2. Use of heat recovery ventilation (HRV) with low electricity use. Extra costs of item 1 and 2 are only 10.000 – 15.000 DKK per apartment (1.350 – 2.000 Euro), based on use of a new thin EcoVent HRV unit which is easy to integrate. This is considered the cheapest way of obtaining the new Danish 2006 low energy demands with a 25 – 30% reduction in energy use.
Experience from realised Danish housing projects has shown that item 1 + 2 alone can lead to a 50% reduction of the yearly heating bill and an improved indoor air climate without moisture problems.
3. Use of low energy windows with a good daylighting transparency and at the same time avoidance of overheating problems.
4. Use of solar domestic hot water (DHW) system to obtain a 50-65% reduction of the energy use for DHW. Extra costs 10.000 – 25.000 DKK per apartment (1.350 – 3.300 Euro).
5 Use of Photovoltaic (PV) modules to reach a desired or even a climate-neutral low-energy level.
With 0.5 kWp PV panels, equal to 3.5 m² crystalline PV modules, a low energy class 1 quality can be obtained for the rooftop dwelling (50 % better than building regulations demand). Extra costs today 20.000 DKK (2.700 Euro).
With an extra 2.0 kWp PV panels, equal to 14 m² crystalline PV modules, a zero energy and climate neutral energy design can be obtained on a yearly basis.
Extra costs today 100.000 DKK (13.300 Euro).
The use of PV energy is considered a very interesting energy option, because we know that we need to depend on renewables in the future and also because there has been a trend of a 50% price reduction in a 7 year period.
In Germany 30.000 new jobs have been created in this industry in the last few years.
6. Use of an adapted energy supply for heating and DHW.
For a low-energy class 1 housing unit you only need a very small energy supply level on a yearly basis. All existing energy supply options can in principle be used (gas furnace, district heating, a small heat pump or electric heating). When a small air and solar roof based heat pump is used you obtain a good energy “quality” and at the same time avoid a separate energy supply (besides electricity). A competitive investment cost of the energy supply system at around 25.000 – 30.000 DKK per apartment (3.300 – 4.000 Euro) is possible. In any case it is very important to avoid heat losses from the energy supply system because a normal-size heat loss will mean a much higher relative percentage in low-energy dwellings.
3. SOLTAG power roofing and new CO
2neutral passive house – housing project in Roskilde
Based on the very good results from the realised SOLTAG CO2 neutral rooftop apartment (receiving the Danish Energy Saving Price 2005 and the Energy Globe Award for Denmark 2006), and which is now placed at the entrance to the Velux company headquarters in Denmark, it has now been decided to go into the development of a modular system for SOLTAG power roofs which can incorporate all necessary functions (PV electricity, solar thermal, daylight, ventilation, insulation etc.).
At present Velux already have modular systems for their roof windows and solar thermal collectors but a modular system which can also be used for PV production is missing.
Fig
3.1 Soltag prototype. Bredablik SOLTAG passive house design.
During 2007 a SOLTAG power roofing secretariat has been established at Rubow Architects in Copenhagen and besides the actual work on developing new SOLTAG power roofing solutions on a new passive housing project (Breidablik) with 24 dwellings has been prepared to be established in Roskilde near Copenhagen.
Here it is the idea to utilise a new developed SOLTAG power roofing system as basis of making the housing project CO2 neutral.
The here mentioned activities and the general work on passive housing and SOLTAG designs are also very important in relation to a new Danish co-ordinated, EU-Concerto project, Green Solar Cities, where there will be demonstration activities in Valby in Copenhagen as well as in Salzburg in Austria. (See
www.greensolarcities.com ) [2], [4], [7], [8].
4. Proposed low energy classes for passive houses in Denmark
The German passive house standard is with respect to energy use for room heating a very strong tool to realise low energy building projects in the future where heating of a housing unit can actually be obtained by help of air heating. This can be done from the air you will anyway supply through your balanced heat recovery ventilation system (with 10 W/m² in energy supply).
In the same way the new Danish energy frame value system can also be considered as a strong tool to support low energy building. Here you calculate the energy frame value by adding the energy use for heating and domestic hot water together with the electricity use for operation, where the last item is first multiplied by 2.5 to take into account the higher primary energy value of electricity.
This is especially true for the new introduced minimum demand values combined with the use of the low energy classes 2 and 1 which at the same time are presented as the expected new minimum demands in year 2010 and 2015.
Since the passive house standard for room heating with15 kWh/m², year is approximately 40 % better than the typical room heating level, connected to low energy class 1, then it is suggested that the low energy class level that is connected to a passive house design should also be better than low energy class 1. One idea could e.g. be to propose 3 improved low energy classes connected to passive house projects. This could e.g. be:
A: 50 % of low energy class 1
B: 33 % better than low energy class 1 C: 25 % better than low energy class 1.
Here B represents an improved level which has the same increase in the energy frame value as low energy class 1 has compared to low energy class 2.
As an example of how this would work we can look at a 160 m² house which according to the Danish energy rules has an energy frame value of 70 kWh/m², year + 2200/(area) m² = 84 kWh/m², year which means that low energy class 1 will be 42 kWh/m², year. If we then choose a passive house low energy class B then the energy frame value can be calculated as: 42 kWh/m², year x 0.67 = 28 kWh/m², year with 15 kWh/m², year for room heating and use of domestic hot water with 6 kWh/m², year inclusive of solar DHW heating. Then there is only left: 28 – 15 – 6 = 7 kWh/m² year for electricity use for operation of pumps and fans.
To be able to have a reasonable value of 4 kWh/m², year for electricity use for operation equal to 10 kWh/m², year the difference of 10 – 7 = 3 kWh/m², year can be covered by help of PV-modules. This is equal to 480 kWh/year or in electricity 480/2.5 = 192 kWh/year. This can be covered by 0.25 kWp PV-modules equal to 1.5 – 2.5 m² PV-modules.
References
1. Pedersen, P. Vejsig (2006). CO2 neutral low energy housing by help of PV- modules ISBN nr.: 978-87-90314-40-8.
2. Pedersen, P. Vejsig, Ingeborg Strassl (2008). Green Solar Cities. Paper for International Solar Cities Conference 2008 in Adelaide, Australia.
3. Pedersen, P. Vejsig (2002). Solenergi og Byøkologi, Nyt Teknisk forlag
4. Pedersen, P. Vejsig (2007), Green Solar Cities, Description of the EU-Concerto II project, Cenergia, Herlev, Denmark
5. Pedersen, P. Vejsig (2007), Solar low energy building in Denmark, SB07 Conference – Torino – Italy, 7th – 8th June 2007, Cenergia, Herlev, Denmark.
6. Pedersen, P. Vejsig (2006), SOLTAG CO2 Neutral Rooftop Apartment, Cenergia, Herlev, Denmark.
7. Pedersen, P. Vejsig (2005), PV and Architecture – Solar City Copenhagen, Solar City Copenhagen, Cenergia, Herlev, Denmark.