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\begin{document}

\title
{Second remarks on a pilot project of renewing the
Obl� 14 house in Brno, Nov� L�skovec}
\authjenhv
\date{May 7, 2003}
\maketitle

\tableofcontents

\section*{Introduction}

Describing my English text made in a hurry as a very crude draft has 
proven, unfortunately, true. Namely, some new sentences, missing in the 
Czech draft, have not been printed into the pdf file (due to my error). 
There have been contained just in the \LaTeX{} source file as parameters 
of the command \verb"\new". I repeat them here and add comments on the 
Lari et al commentary from 2003-4-29 (document AV-513-07.pdf).

I agree with the commentary mostly, so some sections remain empty. 
Still, I leave them here, to retain the numbering.

A reaction on the proposal concerning the measurement should be included 
as well, but it remains to be done. Just generally, I consider the 
measurement proposal as hardly sufficient. A total lack of information 
of what happens in the already renovated houses Obl� 4 and Kam�nky 6 
became a grave problem and this should not be repeated. With lots of 
data, the Obl� 14 project could become an invaluable source of 
education and an opportunity to become involved for a generation of
students and even postdocs. And even for some inhabitants maybe. 

\section{Ventilation}

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

I admit that using the whole shaft, divided into halves, as the 
vertical ducts may not be easy. Still, this is the solution which 
should be examined, as it brings substantial advantages. The only 
problem is, if it is possible to made it tight enough, in spite of all 
the pipes and wires going through its walls. It remains a challenge,
which, in  case of a success, would affect the future development of
passive  house technology. 

The main advantages are:
\begin{itemize}
\item a negligible dynamic pressure loss over the height of the house,
making any necessity to install throttle valves and to tune them up so 
that all the flats would be able to get just the wanted 90\mc/h.
The fire valves would be needed of course, producing about the same pressure
drop.

\item due to this negligible loss, the flats would become truly 
independent, as the air fluxes are regarded (limiting the flux in the 
top flats would not mean any rise in the flux in the flats below 
them)

\item Of course, the electricity efficiency would rise, detaching 
itself from the obligatory passive house limiting value

\item In the duct, no noise at all would be produced -- with the 
corresponding comfort gain for the flats
\end{itemize}


The objection, that convection in the ducts could make a problem, can 
be evaluated from this point: the surface of each duct would be some
35\ms{}. With an insulation of just 2\cm, the thermal conductivity of 
the walls is some 70\,W\pms. Even with the extreme possible 
difference of the 
fresh air temperature from the building temperature (16\degC{} compared 
to 22\degC), the heat flux to the fresh air would be some 400\,W. 
The air going down the duct, some 0.2\mc/s, would be heated by less 
then 2\,K. The only result would be, that the availability of a cool 
air in the bottom floors would be reduced a bit. Of course, just in 
case that central preheating would be abandoned, otherwise there is no 
influence at all, even almost no convection. Such a problem simply does 
not exist at all.

From the old text I quote just one paragraph, where a remark on the 
pressures have been missing:

``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.''



\subsection{The ventilation should be adjustable}

The case for lowering the ventilation rates and getting much more 
comfortable humidity has been strengthened by a participant of the 
seminar in Vienna (and of the broader Austrian team): he and a doctor 
of medicine, who is interested in the problem, think too, 
that 60\% humidity is much better then just 40\% one.

There remains no large controversy -- we agree that the ventilation 
should be adjustable. I would still insist that simple, perfectly 
visible adjusting devices (doors) at the outlets, are far better than a central 
adjusting, esp. if it would be electric (and therefore hardly working 
forever and hard to check how it works). Mechanic device, resembling
traditional control of upper ventilation  windows (not in this house,
but in the old ones everywhere), is  understood by everybody, its
position visible from the room with the  outlet, and is easy to make.
Yes, it would be another new, very useful  part of passive houses
technology. The only reason for an electric control would be, if it 
would enable easy central monitoring of the 
positions of the valves.

In the old text, two remarks were missing, so I quote the corresponding 
paragraphs:
 
``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. 
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}.''

``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.''

As follows from the second one, a mechanic door at one inlet as well, in
the bathroom, would be useful.

\subsection{Central preheating of the air}

The controversy is not visible well in the answer: in my concept, the 
radiator circuit would be running all the time. Not just as an 
alternative
 possibility to heat the building when the ventilation
system would not  work. Overheating should be excluded by another means
-- by the  measuring and accounting system, or even by controlling the 
heating water temperature centrally. 

The radiator brings some comfort as well: it's nice to have a warm 
surface at home. To heat the hands, to dry wet shoes. 

The problem of a possible condensation of moisture in the shaft is no 
problem at all. Such a phenomenon can never happen. The Czech air has 
never a dew point over 22\degC, the minimum possible temperature to 
which the fresh air could be cooled by the heat recovery system in hot 
summer. Even if in the future an option to cool it further (e.g. using 
the cold available in the potable water to be preheated) would be
implemented, the condensation would not happen further in the duct, as
the walls would be always warmer. Such a cooling is not so important 
now, but may become in future, as the climate change proceeds. 

\textbf{There is of course another problem of moisture, namely on the
entrance filter for the fresh air, as mentioned on the seminar in
Prechtlsaal on  April 28. Preheating the fresh air just as in the case
of anti-freezing measures seems completely reasonable whenever the fresh
air humidity is over say 90\,\%. One kilowatt would do, rising the 
temperature by 1\,K before the filter.} Of course, that one kilowatt 
would give just 0.2\,kW useful heat to the building at the end, just 
one fifth, like the solarwall considered below. Or even less, if the
heat recovery would have efficiency over 80\,\%.

In the old text, one remarks was missing, so I quote the corresponding 
paragraph:

``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...}''


\subsection{Solarwall}

The efficiency of Solarwall is really quite low most of the time, just 
some 7 per cent, as follows from the old text:

``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.''

The Streicher's simulation did not take into account the existence of 
the heat recovery with the 80\% efficiency. So the Solarwall has not 
the 35\% efficiency most of the time, but five times less.

I try to explain it on an example, for non-physicists. If 
the outer air would have 0\degC{} and the exhaust air from the house 
some 21\degC{}, the heat recovery system itself would rise the 
temperature of the fresh air by at least 16\,K, i.e., to 16\degC. The 
same increase can be reached by the Solarwall itself, without a heat 
recovery unit, as Streicher's example says. The heat flux to the fresh
air needed to perform this  rise of temperature is some
16\mtimes0.8\mtimes1.3\,kW, i.e., 17\,kW.  When the Solarwall is in a
series with the heat recovery unit, the  fresh air is heated 16\,K by it
at first and then another 4\,K by the  heat recovery unit (80\,\% of a
5\,K temperature difference of the  exhaust and preheated fresh air).
The difference between using just the heat recovery unit and a recovery 
unit with a Solarwall is just those 4\,K, i.e., the Solarwall adds just 
4\,kW. 

How is this possible? The exhaust air (Fortluft) is not cooled so much 
as without the Solarwall, and so 4/5 of the original gain from Solarwall 
go lost in form of rather warm exhaust air (it escapes into the 
0\degC environment with still 17\degC...).

The only full exploitation of the Solarwall gains would happen if the 
outer temperature would be some -20\degC. Then the preheating by 16\,K 
would be used completely, as an anti-freeze measure. However, this is 
not very usual situation... 100\% use of the solar gain by the 
Solarwall happens just when the preheating by it rises the temperature 
of the fresh air just to a couple of degrees below zero. It happens 
often in winter cloudy days. However, in the sunny days the 
efficiency sinks to a half, third or even fifth of that (as the outdoor 
air temperature nears the freezing point).

Anoher full exploitation might be possible using a heat pump for 
preheating the potable water (like in the well known compact units for 
passive houses) by cooling the exhaust air further. This is however 
beyond the scope of the project. Or is it not, perhaps in connection 
with some PV part of the facade?

I am much in favour of using Solarwall here. Just the area might be not
over 50\ms{} -- for demonstration purposes it would suffice. And it 
would not bring (justified) objections by future visitors and interested 
people: ``what an inappropriate use''...


\subsection{Humidifying bathroom?}

Letting just the door open after showering may do, I agree. However,
adding a door to the exhaust air inlet should be a part of the project.
Perhaps as an extra option for the inhabitants, if they want to raise
their comfort and pay for it as well. Just this comfort-raising option
should be  offered by somebody. 


\subsection{Tightness and Blow-door test}

I agree with the simplification to ventilate the cupboards just to the 
kitchen. Simplicity is nice.

In my original text two paragraphs marked as ``new'' have not been
printed, so I repeat them here; they are perhaps not entirely trivial, 
esp. the recommended value of 0.2 volume/h:

``\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 Obl� 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 \emph{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).}''

``\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 display with two temperatures and humidities would be no excessive 
technology, but a very relevant information both for the inhabitants 
and for supervision and publicising the whole project. The outdoor 
parameters will be measured anyway, according to the project, so why 
not make them available to the inhabitants. OK, the LEDs may be abandoned. 

The remaining paragraphs are just quotations from the old text, 
containing some sentences which have not been printed before (as the 
one on outdoor air parameters):

``... 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}

\section{Measurement and distributing the heating costs}

From the consultation at the May 6 meeting it follows, that as the only 
measurement of heat consumption in the old project there  has been a
flow meter on the heating register -- for the air flow being  constant
and also the water temperature being constant the used volume over  the
season would give the heat supplied this way to the flat. However, the
water temperature should be changing over the heating season (and kept 
as low as possible, to avoid drying the air and enabling better solar 
gains), so such a measurement would need online flow meters. With the 
controllable ventilation, this way of measuring fails completely. If 
the heat supplied to the register should be measured at all, a standard 
electronic device would be needed.

I guess that the alternative method, just measuring the temperatures of 
the air (say, of the exhaust air from the flat, which cannot be 
influenced by the inhabitants) online, would be  cheaper, more
just and informative. From the computed heat loss from the flat through 
the building envelope, the energy paid another way (gas, electricity, 
perhaps even warm water) could be subtracted to get really an amount
to be paid for (neglecting the differences in solar gains through 
windows).
 
Of course, the best possibility would be to measure both ways... The 
classic way would favour those ones, who keep lower temperatures and 
need not heat at all (having all the needed heat from the neighbours). 
Without knowing the temperatures in all the flats, we would know nothing 
at all about what the total building consumption consists of, what would 
be rather bad. Quite inappropriate for a pilot project.

Some measurement method which would favour those, who contribute less 
to the building thermal losses, should be a part of the realization in 
any case. The project should specify it of course.

\section{I recommend better insulating and sophisticated windows}

0.8\WsqmK{} should be the limit, including all linear thermal bridges. 
0.95\WsqmK{} is not satisfactory. The results from the Utendorfgasse 
tender show, there are producers which can offer true passive-house
windows for a unit price below 250 euro per square metre.

The option to have shading (and still lower night losses) as an 
integral part of the project, as I propose, seems to be a challenge 
which should not be missed just because lack of any effort. For the 
large east and west window area it's an important matter. The
inhabitants have  Venetian blinds now, at least an option to include
them to the windows  (the inhabitants can pay perhaps for it, rather
then just buy them  afterwards) should exist.

The paragraph from the old text, with a sentence missing in its first 
print:

``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}

My proposal for the whole southern facade is: if the money enable it, 
both sides should be covered by the most hi-tech flat collectors. Just 
the middle cross-like area should use the Solarwall technology for 
preheating (or even complete heating) of the fresh air. Some bottom parts
(as the eastern, most shadowed  corner of the facade, or just the area
below the windows) could and should be covered by TWD (e.g., that by Sto). 

Such a plan would give the maximum energy yield and would minimise 
those parts, which are a bit disputable in this case. Solarwall is 
excellent whenever a mechanical ventilation and NO heat recovery 
exists, but we will have a heat recovery of at least 80\,\%. TWD is a 
costly, but an interesting option, when the facade is not used to heat 
water. But we will use the facade for this purpose and extending the
size of collecting area does not increase the costs so much (or not at 
all, considering the high price of TWD). The  payback times, in
current prices, for each added square metre of water collector replacing
another solar-using or solar-rejecting insulation are below 20 years.

As regards the water collector area, the absorbers should be in series
in those cases, when some are shaded in the morning -- the shaded
should be the first ones. As they will reach stagnation in summer quite
often and their contents will  evaporate, all the pipes should be enough
sloped so that all liquid  could be pushed downwards by the produced
vapour. Unlike in the B�eclav  project, where there is no evaporation
(as no low-emissivity absorbers  are used), the hydraulic connection of
absorbers cannot be changed in  the future. The modules should have the
absorbers sloped according the  wanted hydraulic plan (2\cm{} per 6\m{}
should do I think, perhaps even  1\cm).


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

\subsection{Costs, ``Ertr�ge'', aesthetic kriteria}

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

\subsection{Remark on the collector types}

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

Just a comment for the tender: there is much larger difference between 
the low- and hi-tech collectors then I'd expect before I made the graph. 
At the left end, with zero temperature difference, it's due only to 
using either a standard or a solar glass (with low iron contents and high 
transmissivity). At the usual working temperature difference, 30\,K, or in case of 
such a large system rather 40\,K, the gain is really substantial -- due 
to the much lower emissivity of the hi-tech absorbers. The best ones 
reach a value of just some 0.04, and these should be preferred of 
course over galvanic-treated ones with emissivities of more than 
0.1. 


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

I stress once more: the mixing ventil is obsolete and should be not 
payed for and installed.

\subsection{Remark on glasses}


\section{Thermal bridges}

\subsection{Balconies}

My remark did not consider geometric thermal bridges. The point bridges 
have not been evaluated, as far as I know. Neither in case of 
balconies, nor in case of a lightning conductor. In passive houses such 
bridges are not present, here they are. I guess they may be neglected, 
but a quantitative consideration would be useful. And of course all 
measures to make them lower, as through using the best materials. There 
is not a word about it in the project.

\end{document}
