Ventilation and heating in Passivhaus schools

[Claire Thomas]

(this topic has been split from 'Passivhaus form' http://www.aecb.net/forum/index.php?topic=1871.0)


Nick
I was intrigued to hear your comment about radiators in Passivhaus schools rather than incorporating heating in the ventilation system - is this common practice - in so far as Passivhaus schools can be common ie in Germany!
I'm doing a talk at work on Passivhaus shortly to try and get us to start looking at it for building projects however schools are more likely targets for us than resi - your opinion on how Passivhaus schools are different to houses would be interesting to hear.  
And does anyone know why with the massive schools/academies building programme going on there's no mention anywhere of Passivhaus? It's all nat vent and with noisy city centre sites surely turning mech vent to your advantage is the way forward?
Claire

[Steve Simm]

I was intrigued to hear your comment about radiators in Passivhaus schools rather than incorporating heating in the ventilation system - is this common practice - in so far as Passivhaus schools can be common ie in Germany!
I'm doing a talk at work on Passivhaus shortly to try and get us to start looking at it for building projects however schools are more likely targets for us than resi - your opinion on how Passivhaus schools are different to houses would be interesting to hear. 
Claire

Claire,
I don't know if it's common practice but I know one PH school uses radiators for heating purposes - Aufkirchen - and I believe a few others do as well.  There is excellent information on PH school construction in the 10th International PH Conference Proceedings - PH Schools group section.  In summary they stress the importance of thermal mass in construction to damp external air temperature effects.  In addition they point out the significant differences in occupancy to residential buildings (i.e. dense occupation for a short period of time) and the need to pre-heat in winter time.  I am involved with the construction of a zero-carbon school in Devon which we intend to aim for PH levels of airtightness and energy consumption.  Please feel free to get in contact if you wnat further information.

Steve

[Nick Grant]

Claire

Agree re mech vent for schools, natural seems very hit and miss although there are many enthusiastic advocates. Proof will be in air quality and energy demand when monitored.

Small radiators are the way to go although I have seen radiant wall panels in one passive renovation school. Rads would not be big and contrary to normal practice should actually placed away from windows to reduce heat loss if window opened for any reason.

Working on a library at present and is similar situation. Cold winter day is highest heat load but with few people, lowest ventilation requirement. If heating with air would need to ventilate at full rate when empty to warm it up - wasteful of heat and electric and would struggle in cold weather due to 10W/m2 power limit.

Underfloor heating also inappropriate due to lack of controllability unless the floor is run at only a couple of degrees above desired room temp so self regulating. Would also mean no thermal mass available to mop up the excess gains when occupied and sun shining.

Lots are talking about 'Passivhaus principles' and 'designed to passivhaus levels of energy use' but in my experience this can be very different to the real deal. Need to use PHPP to calculate even if backed up with dynamic models. Reason being, IMHO, that whilst relatively simple, PHPP does take a conservative default view on geometric thermal bridges, internal gains etc. 15kWh/m2/year according to SAP or TAS may be way off real PH performance.

[Paul Teather]

I designed a ventilation system for a community centre/offices last year and decided to take the following route:

Daytime occupancy would be up to 8 people
Weekly peak up to 30 people
Events up to 100-150 people.

There is a baseline ventilation requirement for an empty building to prevent build up of pollutants (although defining what this is is not so clear). Each person requires 8l/s (Domestic is 4l/s).

This led to the following design:
64l/s normal operation for the HRV system
Boost capability - 240l/s (Ducting sized for this). CO2 sensors and manual switching, CO2 switching would also have been good but limited budget.

Above this level of occupancy there is no need for heating - even at winter loads, so two summer by-pass fans were added to work above the HRV capability (Building slightly over-pressurised but expect lots of door opening. I also added an extract 'dump' fan in a highly glazed area (option to operate using a thermostat)

Roof lights had trickle vents that could be opened in summer for passive stack

Then the ultimate ventilation option - Open Windows!

For this type of building, or any variable occupancy this stype of multi mode operation is the way I am going.

Thermal mass is an issue for Solar gain / fluxuation mitigation but does need user intervention to control shading and adapt the environment, easier in a home than in an 'institution' type building.

I am considering using a combination of HRV supplied heating and Radiant heat panels. I am also discussing linking the heating controls to a web site that willoperate the heating systems based on a booking sheet for halls.

Having looked at PH for this type of building my view is that you need to model in different modes of operation - I am planning on re-writing parts of PH for this type of requirement (I have written commercial simulation software in the past and, forgive the heresy, the PH worksheets could be easily improved)

[Mark Siddall]

A bit off topic:

Paul,
Have you emailed PHI to suggest the improvements? I've emailed them some feedback and they were most accommodating i.e. will add to list that shall be reviewed for future tweaks of next edition.

Mark

[Claire Thomas]

Many thanks all for extremely useful responses.

In response to getting feedback on nat vent schools, i am hearing that on noisy sites where acoustic baffles have been used the CO2 levels have been getting too high in classrooms and pupils are falling asleep.  Has anyone else heard similar?

Would add a smiley face but there isn't a sleepy one.

[Andy Simmonds]

Is this 'off thread'?:
The zero carbon hub's energy efficiency standard working group(advising ministers) seems to have come up with a min. standard that does not include any form of mechanical ventilation - as this is deemed too difficult to incorporate into a min new build standard + 'concerns' about 'health risks' of MVHR?!. Rather the proposals are based on 'natural ventilation' and an air leakage rate to match, even though there is no proper evidence that natural ventilation consistently provides adequate air quality. Also the heat recovery benefits of MVHR are not being utilised to reduce carbon emissions.

I have not had enough time to really take this in and develop a view of the proposal (saw the draft proposals this week), but it seems ironic that proponents of MVHR claim better air quality and those for natural ventilation claim reduced health risks. The debate is an 'emotional' one and could do with the air quality and health claims being backed up by evidence.

can anyone help - research, monitored projects etc?!

[Matthew Richards]

Hi

I thought I would add to the debate and share some of my recent experiences in designing low energy educational buildings. We have been working with the Instritute of energy and sustainable development from De Montford Uni (professor Kevin Lomas and Malcolm cook) to develop the ventilation strategy on a large post 16 centre in Leicestershire.

Your concerns about indoor air quality for naturally ventilated buildings are correct in my opinion. The typical solution of trickle vents to provide replacement air in winter mode is pretty ridiculous when you consider that they have no calibration, or sophistication - the  too much/not enough syndrome. also, users close them to avoid draughts. My hunch is that many schools fail on indoor air quality in both winter and summer. Also, the nature of funding means that achieving passivhaus fabric standards is nigh on impossible at present.

I am most interested in mixed mode systems that dont rely on mechanical systems at all times. There is also a different approach required for classrooms, and other more communal spaces with communal areas requring more automation. Furthermore increasing IT loads are making some rooms impossible to naturally ventilate. Just too much heat to dissipate if you consider 30 pupils each with a lap top in a room of 54sqM. I think this is a real challlenge unless IT breakthroughs in terms of heat output are around the corner.

In the classrooms we are using an e-stack system. This is effectively a monodraught system with a 2 compartment stack/shaft with 1 of the comaprtments having a low energy fan.  In winter co2 sensors control the minimum amoutn of fresh air brought into the space. As fresh air is brought in at high level it also mixes with the inside warm air to make it more comfortable. In summer mode traditional opening windows provide the fresh air and the e stack acts as passive stack exhaust. In summer the fan can be used for extreme days. A further benefit is secure night cooling though the e stack.

My feeling is that e stack could combine this into a true heat recovery system for winter mode but they are not quite there at present. Larger open plan spaces are more problematic.

One other point on the thread is that we should not be designign buildings (and cheating) on thre fact that they arent used in summer. Future trends suggest that a school will be used over greater periods of the year in future and probably means that many school buildings have a lot of problems already built in.

I would certainly like to know more about passivhaus design for schools!

[Mark Siddall]

Andy,
Are you interest in ANY research or UK research? I have PH Conf papers from 2009 nat vent vs mech vent CO2 was of the scale in the nat vent version, both were super insulated to PH standards - energy consumption was similar. So for me the compromise between MVHR and nat vent is health and well being.

I've been thinking about the possible health benefits of MVHR. Research in Scotland has shown that MVHR helps reduce the causes of asthma - particularly dust mites (research by Stirling G. Howieson). When you consider that asthma is reported to cost UK plc £2.3 billion a year (http://www.asthma.org.uk/search_clicks.rm?id=18&destinationtype=2&instanceid=312760). If MVHR managed to reduce the burden on the NHS, keep people in work and reduce benefit payments then you could be on a winner before you even start to think about the energy/carbon savings. 

Mark

[Andy Simmonds]

Mark,
as you know I have been living with MVHR for about 9 months now, in my near passivhaus refurbished victorian home. First, my own experience:

What I like about MVHR:

1 It consumes only c. 25 watts on middle setting (from the reading off my powersave electricity monitor when I turn it off/on) when running (currently practically 100% of the time) - I accept the argument that using this much electricity is outweighed by the energy and carbon savings from reclaiming c. 80-90% of the heat that would otherwise be wasted from expelled stale air.
2 Air quality is good
3 With windows kept shut I can have fresh air whilst not having to listen to car noises, trains, passersby, etc at night (although sometimes this is welcome - the rattle of the goods train, the drunken conversation reminding me why it's ok to not have a social life based in the pub.. ). However most nights we sleep with a window ajar - why? To hear the wind, hear the birds in the morning - doubt from PHI reseacrh that this does much to our heating energy consumption, and we don't do it in the colder weather.
4 with heating not turned on yet (end Nov) and not sure when we will turn it on, am pleased that the heat recovery (recycling the solar [nature's rhythms - see below] and internal heat gains) is keeping the house at a consistent 20-21 degrees (yes, we are logging temperatures and utility bills to substantiate this)
5 I can open the windows and doors...and even leave them open (people often ask if in a house with MVHR you are 'allowed to open them'), without the whole low energy strategy coming apart - which is nice

The concerns that I understand (but mainly think are silly and probably not the concern of most overworked, over-charged UK citizens, although do have an emotional reality, ) about MVHR  from 'the Romantics' (I thought I was one - but I begin to wonder..):

5  there are no draughts in the house with which to 'connect to natures rhythyms' - unless we open a window. So the nostalgic feelings we remember from childhood (either too hot/ too cold draughty houses) cannot be drawn upon.
6 it is a consistent temperature in the house (see above re natures rhythms, nostalgia etc)

The initial issues that I am interested in research about, although it has not put me off living with MVHR are:

6 is there any validity in health risks concerning air quality arising from poorly maintained MVHR filters - other filter/intake issues
7 as above but relating to potential cleanliness/dustiness issues etc of MVHR ducts over time
8 case studies of air quality achieved in 'naturally ventilated' buildings - domestic in the first instance
7 a comparison of the benefits of MEV (central unit, mechanical whole home, extract only) - with natural ventilation
8 other ventilation strategies, e.g mechanical systems that can also switch to act as natural ventilation systems outside the heating season, without the hassle/security issues of opening windows..

What I dont like:
8 cost of filters - not major, but wish they could just be washed (maybe I am just being wishy washy)
9 extra cost of design and comissioning - but mustn't grumble...

Thanks for your Link, will have a look at it....

[Doug McEvers]

Andy,

I hope your MVHR intake is designed better than the standard one used in the US. What is used here is just a 6" round duct with a hood attached that goes through the outside wall. The opening (intake) is covered with 1/4" hardware cloth and can easily be clogged with cotton from trees and the like. In a cold climate on the coldest days this hardware cloth can also be covered with a layer of frost that stops the intake of air.

What is needed is an intake duct that has a large and easily serviced pre-filter and a MVHR control that reminds the user to clean the filter at regular intervals.

Doug

[Nick Grant]

Interesting observations Andy and we know know why you are so rushed off your feet, relax you have just gained a month, it's end of October not November.

:-)

Nick

[Andy Simmonds]

"it's end of October not November."

Thanks Nick - now that is a really interesting observation.....are you absolutely sure (because that could explain some stuff that I have been finding really weird recently)?

[Andy Simmonds]

interview with Soeren Peper regarding following queries:

'Widespread concern in UK about health problems of poorly maintained MVHR
and tenant ability to understand/operate them.  Can you help with any studies
in Germany or elsewhere?  This is becoming a policy issue at the highest
level. It is vital we make "Comfort ventilation" a positive thing in the
UK.'


He said that this issue was heavily researched about ten, fifteen years
ago, and you will find a huge variety of - German - literature on this topic, by
Wolfgang Feist (still working at the IWU Institut Wohnen und Umwelt -
institute for living and environment) and Witta Ebel, as well as architect
Schulze Darup and Uwe Muenzenberg from AnBUS (Analyse und Bewertung von
UmweltSchadstoffen - Analysis and evaluation of pollutants).

These being the main documents:
- Wolfgang Feist, IWU 1994 Air quality in Passive Houses 'Luftqualitaet im
Passivhaus'
- CD by Schulze Darup ISBN 3-9808428-1-9
- Conference proceedings, 7th Passive House conference in Hamburg, page
191: Article from Uwe Muenzenberg: indoor air quality in Passive Houses
'Raumluftqualitaet in Passivhaeusern'.
- Passive House Institute: Protokollband Number 8 'Materialwahl, Oekologie
und Raumlufthygiene', 1997 = Volume 8 of Research group cost-efficient
Passive Houses: choice of materials, ecology and indoor air
quality/hygiene.

Key is that filters are regularly replaced. In the first Passive House,
this was done, and the ventilation ducts were examined after several
years: no dust, no mould, no humidity insided the ducts.
If there are concerns that users would not change the filters themselves,
then there should be a maintenance contract between the house owner and an
external company to ensure that the filters are changed on a regular
basis.
During construction, a proper site supervision is crucial so that the
ducts are clean at the time they are installed.

[Dave Howorth]

I came across a paper that may be relevant:

Ventilation and health in non-industrial indoor environments: report from a European Multidisciplinary Scientific Consensus Meeting (EUROVEN)

P. Wargocki et al

Indoor Air, Volume 12 Issue 2, Pages 113 - 128
Published Online: 26 Jun 2002

The abstract is at http://www3.interscience.wiley.com/journal/118921079/abstract
I've asked permission to post some extracts from the paper. It's been cited 97 times but I haven't checked any of them yet.

Cheers, Dave