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\begin{document}

\title
{Remarks on a pilot project of renewing the
Oblá 14 house in Brno, Nový Lískovec}
\authjenhv
\date{12. dubna 2003}
\maketitle
%\begin{multicols}{2}
%\noindent

\tableofcontents

\section{Ventilation}

Within the whole project just one part seems to me as being rather 
imperfect: the mechanical ventilation system.


\subsection{Cross-sections of ducts are to be several times larger}

The key for mechanic ventilation aiming at maximum comfort
and preventing energy wasting is using just very low velocities of the 
airflow, and consequently little electricity consumption for 
ventilators.
The upper power limit which a really good ventilation is to obey is 
 0.4~W\pmc{}s. The top-quality (passive)
houses do always obey it (see e.g. Stärz \cite{Starz}). For a 
ventilation with a proposed flow of some three thousand cubic metres per 
second for the whole house (I quite agree with this flow, as a maximum 
one) it implies a maximum allowable electric input of all ventilators 
of just 1.2~kW.

The 0.4~W\pmc{}s value is 
\old{\new
{not contained in the April Czech version}
{probably -- there is one differing 
opinion, and the true installed power and real flows are to be 
checked)}}
considerably exceeded for the analogous renovated houses at
Oblá 2 and Kamínky 6 already, where the airflows are perhaps just half
that large \new{not contained in the April Czech version}{probably below
1800\mc/h, with two ventilators 650\,W each (using Atrea Duplex N2400 heat 
recovery unit)}. In spite of that, the Oblá 14 project supposes
using ducts of the same  size, which are too narrow even in the above
mentioned houses. No wonder that the planned electricity consuption
results unpleasantly high,  quite untenable for a pilot project. There
is a marked difference from   the Prof. Streicher's analysis 
\cite{Schmidl}, which speaks about a necessity to keep the velocities
below 2.5\,m/s (also from acoustic reasons) and gives the needed 
minimum duct cross-sections 
(1.0\dmsq{} for each of the two branches to a flat, 
16\dmsq{} for the sum of the cross-sections of both ducts in a 
shaft).

Fortunately, the remedy is easy and should not add much to the costs.
There is a possibility to have generously sized ducts. By avoiding 
any vertical separate ducts (as pipes) and using the 
\emph{whole installation shaft area as ducts}. It is sufficient to 
separate them in two halves (in a fire-resistant way) and eventually to
attach there a suitable cladding (say a glass wool with an aluminium 
foil at the surface). Even with all the pipes for another purposes
(wastewater, insulated cold and warm water pipes, gas, power and
measurement cables)  the remaining areas are so large that even in the 
top floor the velocity won't exceed two metres per second. In detail, 
the whole shaft cross-section is 4\dm\mtimes8\dm, the insulated pipes
take 4,2\dmsq{} from it, after adding a halving bar between the fresh and 
exhaust air and adding some sort of cladding 2.5\cm{} thick (they will 
take max.
7\dmsq) still over 20\dmsq{} remains.  Even with local obstacles like 
armatures, branches and measuring devices the condition of the flow 
velocity below
2.5\,m/s will be obeyed with a good safety margin,

The only condition of the functionality of such solution is a sufficient
tightness of the control doors to the shaft in each flat. There should 
be two doors, to each duct separately, ideally made in such a way that 
it would not be possible to open both of them at once (a shortcut would 
result and the ventilation would cease to 
work, \new{not contained in the April Czech version}
{the wanted pressures in the ducts could not be maintained, 
what should be indicated by a measuring system}). A switch indicating 
which door is not properly closed would be suitable, attached to the 
whole measuring and control system accessible by Internet.

The reason to use vertical ducts of just 20~cm diameter in the 
preceding reconstructions has been the wish to avoid the necessity of
installing fire valves to each flat. The current project includes such 
valves already, so there should be no obstacle for using large 
cross-sections for vertical ducts. The pressure losses per the house  
height should be not over three pascals, and the necessity of any 
initial balancing (or regulation) of flows into the branches in 
various floors would disappear. The varying distances to ventilators 
should play almost no role, the pressure drop on the outlets and 
on the input filters for exhaust air (they are maybe not included in 
the project, but I'd be in favour of them, also because of their 
acoustic damping effect) should perfectly do.

The project should be adapted also as the branches cross sections are 
concerned. The Streicher's value of one square decimetre for each 
(fresh and exhaust air) one is lower limit, double cross-sections are 
better, to keep the velocities pronouncedly below 2~m/s. If possible, 
all the components should have such a generous size, incl. the fire 
valves and the heater. A suitable diameter for circular ducts would be 
15~cm, but a solution without any pipes would be much better -- using 
suitably divided false ceilings (from gypsum boards probably) of the
central parts of the flats. 

The project does not contain ducts to the pantry cupboards, pipes of an 
inner diameter of just 4~cm might do, see in more detail in the part 
Tightness and the Blow-door test. 

Of course, even on the roof should be the ducts large enough, having
approx. four times the cross-section given in the project.

There is no data on pressure drops on the proposed recuperators and 
some other components. Maybe, it will be necessary to choose another 
devices, ensuring velocities below 3~m/s.


\subsection{The ventilation should be adjustable}

The project goal to lower the heat losses so much, that no classic 
heating system is needed, is surely good. But as the project wisely
includes  letting one radiator inside each flat, we can think about the 
possibility than not all the heat load is to be always supplied just by 
the fresh ventilation air. 

It has namely one unpleasant property: it has to run full strength
just on those days, when it desirable to ventilate as little as 
possible, from a viewpoint of hygiene (and of energy savings).
I mean the case of frosts, when the fresh air contains less than 
four grams of vapour in a cubic meter. After being heated to 22 degrees
(a common temperature in passive houses, see e.g.
Thür \cite{Thur}) its humidity sinks below twenty per cent. But the 
ventilation is to rise the comfort, not to lessen it! By diminishing 
its rate in chilly weather the interior humidity can be raised to the 
beginning of the comfort range, at least to forty per cent -- assuming 
somebody lives in the flat and so there are sources of humidity, as 
respiration (people themselves humidify the air from 20 to 40~\%, if there are 
just 10\mc{} of fresh air per hour and person). 

By lowering the air exchange rate and the subsequent rise of humidity 
the inhabitants will perceive the interior temperature as suitable even 
if the air will have just 21\degC{} instead of 
22\degC, thanks to the diminished cooling of the skin by evaporation. 
Zdùraznìme, ¾e ani
Let's stress that even an incidental humidity around sixty per cent 
(entirely common in summer) cannot, in such a high-quality house, make 
any hygiene problems in winter, as there will be no cold surfaces where 
the water could condensate. 
Aside from getting a higher comfort, the fire risk will diminish\new{not 
contained in the April Czech version}{, when 
the humidity will be kept high}.

On the other side, the needed maximum heat input (10\Wsqm, i.e.
0.6~kW per a flat) may be easily supplied by a single radiator. 
Due to a missing thermal insulation inside a flat and a thanks to a thorough 
insulation of the building envelope, it is not very important where 
that radiator is placed.

Especially during a longer absence (winter holidays) it is suitable to 
reduce the ventilation of a flat, say to one tenth or even less, and to
let some slight  heating (not needed for the given flat, but considerate
to the  neighbours) to the radiator. The flux-reducing device can be
mounted  onto the outlets \new{not contained in
the April Czech version}{and definitely on the bathroom exhaust 
air inlet}, or in need just centrally into the branch from the vertical
duct. To put it on the outlets has a large advantage: it  enables, e.g.
at night, to ventilate generously just those rooms where  somebody is
sleeping in and to prevent drying another rooms in vain.   

Controllable ventilation in the flats implies a necessity to regulate 
the power of the fans. The easiest regulation is to keep a constant 
pressure difference (against an outer air) in the main duct just before 
the recuperator. In this case the airflow in each flat will be 
independent on the ventilation settings in the other flats. The 
regulation will bring further electricity savings. The pressure 
difference can be centrally lowered when the temperature sinks below 
zero, to avoid the need to lower it individually in all the flats to 
reach some comfort level.

(Such a central reduction of pressure differences 
can be inappropriate just if there are smokers in some flat, who smoke 
in a room from which the air goes to another living places and the inhabitants 
want to dilute it by the fresh air as much as possible. During a 
diminished ventilation period they could do it by opening the windows, 
what should be quite exceptional and short-timed in a frost. So it is a 
topic to be further considered. \new{not contained in the April Czech version}
{Maybe the experience shows what's 
the best strategy.})



\subsection{Central preheating of the air}

One important preheating is missing in the project, namely the 
anti-freezing measure. The exhaust moisture should not freeze at the 
recuperator outlet. A bypass for the fresh air is another solution, but 
preheating can be simpler and more reliable. It's easy to make it by a
a register using the freeze-resistant (solar) circuit. \new{not contained in the April Czech version}
{It would 
have excellent efficiency, as the solar collector could have a working 
temperature of perhaps zero degrees...}

On the other side, the heater on the outlet of the fresh air from the 
recuperator is very disputable. There is no need to heat the air to
twenty degrees. At least at night it should be switched off, so that 
people who want to have a less warm bedroom could have a chance to get 
it, without opening the window (this should not happen, as it is 
reaction to overheating in fact). They can't get a cold air anyway,
having a heat-recovery efficiency of 0.8 (if the recovery unit won't 
use a bypass as an anti-freeze measure), the least possible temperature 
is sixteen degrees. 

The heating registers in the flats will be able to heat the air by 
thirty degrees, they will be able to heat it by thirty four as well 
when needed. But they need not, there will be a radiator in a flat.  The
simplest solution is therefore, to  \emph{abandon the central heating
behind a heat recovery unit  altogether}.


\subsection{Solarwall}

Preheating (or, sometimes the whole heating) of the air 
by the solarwall seems to be very low-efficient together with a good heat 
recovery. Really, from the heat gained by the solar wall just 
twenty per cent would be used most of the time. The full thermal gain 
could be used just as an anti-freeze protection of the heat recovery 
unit.

This is a large difference of the solar wall (a bored black sheet metal)
from a warm-water collector. The gains of the latter one 
would be used completely in winter.

On the other side, the solar wall should have a comparable price to the 
common wall insulation -- the present one contains mineral wool and 
sheet metal cladding as well. It won't be the case in this project 
probably, as there seems to be no producer of suitable bored sheets in 
Czechia. The solar wall at Oblá 14 should become an important impulse 
toward Czech enterprises to start with its production. For buildings 
without heat recovery, but with a mechanical ventilation, it is namely 
the best solution for the insolated facades, apart from the windows, 
with a short payback time.  

Replacing the solar wall by using a hi-tech warm-water collector on 
the other side of the facade as well would be rather expensive. A lower 
insolation of the eastern half of the facade speaks against it as well, 
as it is almost half a day partly shadowed by a large tree -- for 
cheap black sheets it's no pity (just it is necessary to place it at 
the eastern half of the facade). 

In spite of that, considering all possibilities for the southern 
facade, I'm in favour of this alternative. Both continuous parts of the 
facade should be covered by a warm-water collector and just the 
cross-like areas between the windows should be covered by a Solarwall 
(like they are now, apart from the holes and black paint...). 
\new{not contained in the April Czech version}
{To demonstrate a transparent insulation, just the lowest part of the 
middle section of the facade should do, or perhaps a lowest part of the 
eastern continuous area, instead of a water collector. The transparent 
insulation is not at all as efficient as a hi-tech facade water collector, 
with a comparable price, so the area covered by this way should remain 
small.}


\subsection{Humidifying bathroom?}

A less significant topic is an installation of a circulation ventilator
in a bathroom, which would blow the vapour usefully to the rooms in chilly 
periods, instead of discarding it to the exhaust air. 
It's again a comfort-beneficial measure. The bathroom air is often free 
of unpleasant odour, and to rise humidity with no cost is always good 
in winter. 
60~\% is better than 40~\%. 

During the cold periods the exhaust air inlet in the bathroom 
should be opened just in case somebody wants to use the bathroom as a 
quick drying room. 


\subsection{Tightness and Blow-door test}

The basic condition of a functional and efficient ventilation with a 
heat recovery is, that all the air goes really through the 
recuperators. It means that there should be no 
other persistent ways for the air from the house and out of it, i.e., 
that the house should be tight otherwise. 

It is never sufficient to assume it, but it's necessary to prove it.
During such a proof, called a blow-door test, there are always some 
splits found and sealed. So long, that the air influx through then
sinks below six tenths of an apartment volume in an hour, with a pressure 
difference of fifty pascals
(see e.g. \cite{Feist}), really achieved tightness is usually twice 
better.

\new{not contained in the April Czech version}
{HOWEVER, this conventional limit for passive houses (or for a 
suitability to use heat recovery) is quite insufficient for a 
multi-storey building like that on Oblá 14! Namely, in a cold winter 
period, the pressure difference between the outer and the inner air
would amount to more than thirty pascals at the bottom floor. Most of the 
air would go in through the remaining cracks, instead of 
through the fresh heated air supply. Cold draft, lost of comfort and 
heat losses would result. Such a high building, with a central 
ventilation system, is to be at least thrice tighter. So the allowable 
limit is just \textbf{0.2 volume/h at 50 Pa}. It holds both for the 
bottom storeys (greatest convectional air suction) and for the top ones 
(largest wind velocities).} 

Because of the giant volume of the house it's recommendable to test 
each flat separately. And the bottom floor. At the end the tightness of 
the staircase is to be checked, i.e. of the all flat doors. These doors 
have to be very tight.  

A blow-door test is an easiest proof if the house
has been repaired without faults. It's especially important by 
such a plate concrete house, where the connection of panels are 
notorious for the cracks.  

The holes to the pantry cupboards would make a great problem
Their existence is in a sharp conflict with the idea of heat recovery.
The openings through the building envelope, contained in the project, 
have to be abandoned. The cupboard is to be ventilated by a separate 
branch for the exhaust air -- and as the presence of smokers near them 
is difficult to exclude, even the supply of fresh air should exist.
Thin pipes, with a cross-section of just quarter of a square decimetre, 
should do.  

\new{not contained in the April Czech version}
{When the ventilation system will be finished, an easy way of a
tightness test is possible: by closing the fresh air supply. Just a way
of measuring the airflow of the exhaust air should exist, a reasonable
option even for the normal operation of the system. (Another airflow
measuring device should be in the fresh air -- in this way, inferring
from the flow differences in freezy periods, any untightness in the 
bottom half of the building would be apparent.)}


\subsection{Opening windows and inner insulations}

... A suitable information would be a LED indicating that it's not 
suitable to let the windows open, fully or partly. It could be a part 
of a large display, reporting the middle temperature and humidity of 
the flat \new{not contained in the April Czech version}
{and the same parameters of the outside air}, see further below. 
Two degrees of unsuitability could be given -- the first saying that 
the heating runs or that it's too hot outside, the other warning that 
the energy losses through the untight window become substantial.

One of the reasons for opening the windows has been given
already in the part on the disputability of the central heating of the 
air up to twenty degrees -- namely the effort to cool down the bedroom. 
Apart from abandoning the central preheating, one other measure seems 
reasonable. It can but needs not be an integral part of the renovation.
I mean adding some inner insulation. Up to now, the outer envelope 
has been so conductive, that the inhabitants of neighbouring flats 
could keep the inner temperatures quite different, according to their 
wishes. But by the thorough outer insulation the building will become
almost isothermal, the thermal resistance of the ceilings and inner 
walls will become negligible. \new{not contained in the April Czech version}
{Interestingly, it could lead to a 
loss of comfort for some people.} The solution is to put some 
centimetres of insulating material on the walls and ceilings. 
\new{not contained in the April Czech version}
{Even thick carpets could help a bit.} Another option is insulating 
just the bedrooms, even from the surrounding rooms of the same flat. These 
insulations could be acoustic ones, as well. 

Modular insulation (as some 1.5\m{} wide, in the whole height of the
rooms) with a wooden frame and filled optimally by sheep wool (there are
two certified Czech  producers of woolen insulations), with a finished
surface in various  variants, according to the wish of the inhabitants,
would be perhaps  the best possibility. The inhabitants should have an
offer to order and  pay for it themselves. \new{not 
contained in the April Czech version}
{If they know there are
no differences of thermal  preferences in the neighbouring flats at the
moment, and no wish to  have a cold bedroom, there's no need to install
them now.}


\subsection{Roof room ventilation}

The planned room for the new heat technology on the roof has mechanical 
ventilation in the project. This is obsolete, a convectional 
ventilation is completely sufficient, just in freezy periods it should 
be damped very much. If the occasional workers wouldn't feel well 
there, an open door and another opening at the opposite side (a window, 
even if the project says no windows) would change the air there in a 
moment. 


\section{Measurement and distributing the heating costs}

In a house with a well insulated envelope there is no much sense in 
measuring the heat delivery to each flat, as far as the payments for it 
are concerned. In this way the inhabitants, whose neighbours try to 
have a lower temperature at home, would be penalised.

A fair accounting of the heat consumption, reflecting the true 
contribution of the flat to the total heat demand of the house, is just 
that one, which is based on the difference of inside and outside 
temperatures during the time when some heat is supplied. These 
temperatures are to be logged. Such a praxis has been described by  
M. Los \cite{lomex} in the projects in Blansko (a town some 20 km N of 
Brno) in mid-nineties, with a pronounced decline in the building heat 
consumption and a maximum satisfaction of the inhabitants. Such an 
accounting virtually eliminates overheating (this system won a  
Grand Prix on Pragotherm 2003). 

The condition for the system to work perfectly is that no windows remain 
unclosed in the house, i.e., the whole air from the flats flows through 
the heat recovery units. This is fortunately relatively easy to check, 
if the humidity is logged together with the temperature. Opening the 
windows in the cold period manifests itself by lowering the humidity in 
the flat.

Both values from electronic sensors, temperature and humidity, should 
be very apparently visible in each flat, the inhabitants should be able 
to see their history also. The collection of these data should be 
accessible (without recognising which flat is which) online on Internet 
as well, together with another values on the house operation. 

The display in the flat could show another values as well, esp. 
temperature and ev. humidity of the outer air (the users of the 
southern flats have no possibility to measure in the morning resp. in 
the afternoon, as there is no place in the shadow). The difference of 
the outer and inner temperatures implies if opening the windows is OK 
or unsuitable (a separate indication of the same fact would be useful 
as well, see above).


\section{I recommend better insulating and sophisticated windows}

The project proposes windows with still rather large thermal 
transmissivity. For passive houses, there is a limit for a maximum 
specific transmissivity 
(a total one, incl. frames etc.) 0.8\WsqmK. Just when this is reached, 
there is no more need to have a radiator below them. 
The 1.1\WsqmK{} value given in the project would result in unpleasantly 
cold window surface, which could be compensated just by an overheating. 
I know no way of advocating such a high transmissivity of the windows 
against an objection that it is an error in the pilot project. 

It's possible to reach the usual limits for passive houses  simply by a
triple hi-tech glazing. For the frames, one possibility is their subsequent insulation of
even the movable parts (the fixed ones should be
insulated  completely, not up to the remaining two centimetres, which
were left  uninsulated on the previously renovated houses, as on Obl
Oblá 2). Another possibility is using such frames, which insulate 
enough themselves already.

But the triple glazing needs not be a standard one, filled all with 
krypton. Contrary to that, I'm in favour of a solution which a pilot 
project would deserve. I mean that the first cavity should be an 
air-filled one, with an aluminium Venetian blind, unpainted (!), moved 
even automatedly, electrically. The ideal blind would contain myriads 
of very small holes, so that the view through it in a closed state would
be still  possible. I saw such a kind on the Wels fair. By closing a 
blind overnight the passive house limit is easy to reach (assuming the 
second, interior cavity is the standard hi-tech one). At the same 
moment the escape of the light outside is prevented, what means more 
light inside and less light pollution outside.  

Including the blinds into the project is necessary, as the main window 
area is not precisely southward, but the most inadvantageous eastward 
and westward one. These orientations causes overheating in summer.
The only efficient remedy are just clear aluminium reflection surfaces, 
installed as outwards as possible. \new{not contained 
in the April Czech version}
{If we won't choose the 
expensive possibility of outer ``Rollades'' (with unpainted Al surfaces 
again, of course),} the blind should be in the outer cavity of a triple 
glazing, so that the sun-heated glass (each with a hi-tech layer of a 
low emissivity is heated a lot by sun) does not heat the interior.  


\section{Solar system discussion}

is no polemics with the project, but its support... just the question 
of the planning of various surfaces on the southern facade is opened a 
bit. 

......... (the translation of the following subsections is obsolete for
readers with a profound  knowledge of solar technologies)........., 

\subsection{A substantial part of each building is to be a solar collector}

\subsection{Costs, ``Erträge'', aesthetic kriteria}

\subsection{Dimensions and using the rest of the facade}

\subsection{Remark on the collector types}

The business people in Czechia and Germany often claim, that ``more heat 
can be obtained with vacuum collectors, esp, in winter'',více tepla lze získat 
pomocí kolektorù vakuových, hlavnì v~zimì``. This statement could hold 
in the times when no good selective absorbers were used (i.e. such 
ones, which cool little or just negligibly by radiation). Today such 
a sentence is not true a long time already. Heating of a 
potable water or building heating means using temperatures below sixty 
degrees, and from a given facade or roof area it is always possible to 
get more heat when it is covered by hi-tech flat collectors 
(with vacuum-process deposited dark films on absorbers and covered with 
a ``solar glass'' without an iron content). A graph illustrating this
feature gives an efficiency of heating per brutto area of the 
collector. 

The reason is that using vacuum tubes the maximum absorption area
which can be placed on a given facade is rather low. The vacuum tubes 
could supply more heat just for working temperatures always over eighty 
degrees, it means for some other technology purposes. Of course not 
cheaper than flat collectors, because of their much higher price, 
vacuum tubes can be more 
economic just for working temperatures a lot over hundred degrees. 

\noindent
\includegraphics[width=\textwidth]{rapkols_en}

The graph is a synthesis of the data published by a solar test facility 
in the Swiss town  
Rapperswil \cite{spf}. It displays the roughly best types of flat and 
tube collectors. As for the  
low-tech collector, the data are taken from the first brochure by the
Arsenal Research from Vienna (study \cite{weiss} gives a higher 
efficiency of a  
low-tech collector, an unrealistic one in my opinion, with a
``\emph{k}'' lower than 5\WsqmK). For the bare absorbers, 
the author's estimates are shown
(\emph{k} or \emph{U} 13\WsqmK, resp. 20\WsqmK). Solarwall, i.e. the 
bored sheet metal, should have an efficiency close to the lowest curve, 
according to the link given in \cite{Schmidl}.

\subsection{No heating of the warm water over 60\degC{} is needed}

The project mentions a periodic heating of the water over 60\degC, 
as a prevention of legionellas proliferation. This is obsolete, a tight 
water pipeline system in Brno has always a chlorine surplus, which 
excludes a presence of bacteria. If the water temperature gets never over
60\degC, no mixing ventil is needed to save the users from getting 
boiled. (Apart from this, there can be doubts if heating below
80\degC{} sterilizes water substantially, but it's not important here.)

\subsection{Remark on glasses}

Solar collectors are assembled with e tempered glass of 4\mm{} thickness. 
It's something different from giant thick non-tempered glasses used as 
``glass facades''. I've noticed a mention somewhere, that the supposed 
thickness is
8\mm, such a solar glass (without iron) does not exist maybe, and if it 
does, it would be very expensive (so as its holding in the place).


\section{Thermal bridges}

\subsection{Balconies}

There is no evaluation of the remaining thermal bridges in the 
projects. The most serious are the balconies, hanged still on steel 
components.  They could be estimated by measuring the inner surface 
temperatures in the houses which are insulated already, but it would 
need cold outside temperatures. Computing them is not reliable due to 
the poorly known area of touch of the both components. There is no 
information on the materials, using the chrome-nickel steel with minimum thermal 
conductivity should be considered. 


\subsection{A roof over the entrance}

The project claims that cutting away the current roof would be 
expensive. I guess that it is cheaper than hiding it inside a thermal 
insulation. Even when insulated, it would still be a large geometrical 
thermal bridge. The area before the entrance would profit from a new 
roof, much larger, just staying by the building. It might be 
translucent or transparent, with four columns. These could be useful 
for both bicycles and people...


\section{Trifles}

I'm not sure if in the ``warm roof'' alternative any expensive XPS 
insulation is needed, instead of EPS.


\begin{thebibliography}{9}

\bibitem{Starz} Stärz, N.: Planungsgrunsätze für
Wohnungs-Lüftungsanlagen, \emph{Erneuerbare Energie, 2003/3}

\bibitem{Schmidl} Schmidl, J.: Energy budget on a demonstration object Oblá 14,
E.V.A., Wien 2003. Made by a team from the University of Technology in  
Grazu, Institute of heat technology, led by 
a.o. Univ.-Prof. Dipl. Ing. Dr. techn. Wolfgang Streicher.

\bibitem{Thur} Thür, A: CEPHEUS (an)gemessene Ergebnisse, 
\emph{Erneuerbare Energie, 2003/3}

\bibitem{Feist} Gestaltungsgrundlagen Passivhäuser, Verlag Das
   Beispiel, 2001, ISBN 3-935243-00-6

\bibitem{lomex} Los, M.: method of accounting the costs of heating and 
 water supply, see \h{www.lomex.cz}

\bibitem{weiss}
Bergmann, I., Weiß, W.:     Fassadenintegration von thermischen
Sonnenkollektoren  ohne    Hinterlüftung, AEE Gleisdorf 2002. Viz
       \h{www.energytech.at/download/endbericht_bergmann_1302.pdf} 
       (209 stran, 3.413 kByte)

\bibitem{spf} Institut für Solartechnik SPF, viz \h{www.solarenergy.ch}

\end{thebibliography}


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