Ventilation With Heat Recovery System Problem Statement Engineering Essay
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Architects don't know so much about ventilation systems and what to think about in the planning - but it's important to think about the ventilation and the demands for it already in the early stages of planning. Enough space for the ducts, the service room and equipment is required and has to be planed in outline phase. It is also important to know where the system will be placed because of the load calculations that have to consider the heavy weight of the system, especially if it is placed on the roof or in the attic.
This should be like a guideline for architects to know which points to check on in planning.
In my own purpose:
I am studying architecture and I'm interested in the topic sustainability and passive houses - so I wanted to improve my knowledge about the different topics related with that.
Ventilation is one of them. I have heard about it a lot, but I didn't know so much about it. It's very new and common in passive houses, so I wanted to go deeper into this topic.
In our modern world were the global warming is a big issue and climate change is the most popular topic in different professions and discussions, green energy resources become more and more important.
In the building industry several new rules and a very tight energy frame making it necessary to plan a new building with the new technologies for low energy buildings.
There are several technologies that can be used in a passive house or buildings of low energy class such as geothermal energy, heat pumps, solar panels and mechanical ventilation with heat recovery system for heating the house and avoiding heat loss. Wind energy and solar cells for electricity. Rainwater reuse, green roofs and the choice of sustainable materials are also things to think about, when planning a modern building.
Mechanical ventilation with heat recovery system is one that is now common in passive houses. It is a method to heat the house or just avoid the heat loss due to the inlet of fresh air through opening up the windows.
Ventilation was in earlier times mainly used to cool the offices and living spaces in warm regions or to get clean air in working places.
But due to the tight energy frame and the fact that most of the energy lost is from gaps in the buildings and opening the windows to let fresh air in, mechanical ventilation becomes more and more common in apartments along with the airtight shelf of the buildings. Today the use of ventilation with heat recovery system is becoming more usual in domestic buildings and multistory houses.
III. Main part
"Ventilation is the process of exchanging indoor (polluted) air with outdoor (presumably fresh and clean) air. Its main purpose is to create optimal conditions for humans in indoor environments, taking into account their health, comfort, and productivity by providing air for breathing, for removing and diluting indoor pollutants, for adding or removing moisture, and for heating or cooling."
From EUROVEN (multidisciplinary group of European scientists)
out of the document: Ventilation and health in non-industrial indoor environments: report from a European Multidisciplinary Scientific Consensus Meeting (EUROVEN)
heat recovery systems explained
Purpose of ventilation is to fulfill the needs of hygiene and comfort. It has to supply air of acceptable quality and control moister and temperature in the room.
definition of heat exchanger
A heat exchanger transfers heat from the outgoing used air flow to the incoming fresh air stream!
3. different systems
There are 6 different heat exchange systems, which I will explain briefly:
cross flow heat exchanger
It has up to 60 - 70 % efficiency.
In this system the heat from the outgoing air is transferred to the incoming fresh air throughout thin sheets of metal with small room in between them.
The incoming air is floating through every second slit and the outgoing air through the rest of the slits in opposite direction. The warm outgoing air is giving its own heat to the sheet and these are heating up the fresh cold air coming inside. There is also a transfer of heat, because of the condensation on the metal sheets.
The two different airflows are completely separated from each other, due to healthy reasons. To avoid overheating there is a bypass for the fresh air which can switched on. Filters to clean the air before it goes through the heat exchanger on both sides are necessary to prevent the metal sheets of getting dirty.
(from: E-book "Baukonstruktionen" (springerlinküberfhA07052010))
Heat pipe - heat exchanger
This system is mostly used in industrial processes.
The heat from the outgoing to the incoming air is transferred throughout a liquid, which evaporates and condensates again.
Composite circuit heat exchanger
If the fresh air supply is in the basement and the exhauster is in the attic this system can be used to have a heat exchange in between the two air streams.
It is often installed in old ventilation systems, which were designed without heat recovery and now updated to the new energy standards.
The heat is transferred with a heat carrier fluid which has to be prevented from freezing, because the outside temperatures can be under 0° C.
rotary heat exchanger
This system provides a heat recovery up to 85% and transfers the humidity from the outgoing to the fresh air.
The heat exchange is done by a slowly rotating heat storage made out of aluminum foil organized in a wavy shape with hexagonal holes. The in and outgoing air is sought by fans in opposite direction through the holes of the heat storage mass, which goes through the stream of outgoing and incoming air. The heat from the used air is given to the heat storage mass and the humidity condensates at the "hygroskopischen" surface of the aluminum foil. When the rotating mass goes next through the incoming cold air it heats up the incoming air and gives the stored humidity to it. Between the two airflows the heat storage mass passes a cleaning phase, where the rest of the outgoing air is blown out of the holes to avoid the mixing of already used air into the new fresh air.
(from: E-book â€žBaukonstruktionen" (Bild vom springerlinküberfhA07052010))
heat pump system
The outgoing air is cooled by an evaporator of a heat pump and the gained energy is used to heat up the incoming air. Because of the fact that there is more heat as needed, this system is also used to heat up the water.
Sometimes a heat pump is connected to a ventilation system after the heat exchanger to heat up the water and have the most heat recovery possible.
earth-to-air heat exchanger
The incoming air is led through the ground and heated up through geothermal heat. In summer when the air outside is more than 22° C it can be used as a cooling system.
This opportunity of heat recovery should only be considered the latest, if everything else is already used.
4. Product examples of two different producers
There are several producers of ventilation systems in different countries of the world.
I think the best way to choose one is to look at the ones in the area of the newly build building (or where the restored/ renovated building is), because mostly the company mounting the system can also do the service of it. And the way to the building site is not too long.
Another opportunity to find the right one is by looking at the products (especially if a certain, special or an innovative system is required) or choose one that is suggested by a college.
Here are two products of different companies:
exhausto - Vex 280
The first on is from the german company "Exhausto GmbH" which is located in south-west Bavaria but international operating.
The system is "Vex 280" with a rotary heat exchanger and heat pump (additional if wanted).
(from the homepage of the company www.exhausto.de)
dantherm air handling - DanX
This one is from a danish company "Dantherm air handling A/S" which is located in Skive and also international operating.
"DanX" is a system that can operate with cross flow or rotary heat exchanger and a heat pump if required.
(from the producers homepage - www.dantherm-air-handling.com)
5. Examples of multistory houses that use ventilation with heat recovery systems
a. Trondheim, Norway
multistory-house as passive-house in Trondheim, Norway
20 apartments (1650 m²)
It was the first multistory house in Finland where ventilation heating concept is used.
It was tested one year and the results proved the targeted energy savings and the good indoor air quality.
New innovative solutions for ventilation in this project were:
"Ventilation heating unit with counter flow heat recovery, integrated optical freezing control and air heating coil for district heat, and DC fans."
(from the document: report from the VTT Technical Research Centre of Finland )
Technical specification on ventilation:
(table with results from the technical research center of Finland)
Multistory house as passive-house in Hamburg, Germany
8 stories & 3 basement stories
19 subsidized apartments (1491 m² heated area) and parking
Central ventilation with heat recovery system cross flow heat exchange system with hydraulic freezing registering
Ventilation service room placed in the attic - 2 down pipe shafts
bypass for summer
air exchange: 1700m³/h
The ventilation system used too much electrical energy because there were problems with the system (the machines) due to missing service of the Service Company which was responsible for the ventilation system. After fixing the problem areas, cleaning the parts of the machine which where messed up and a new service company in charge, the system worked properly again and with the results expected.
C. important things to think about in architectural planing
1. Principles of ventilation
a. displacement system
The incoming air is exhausted into the room throughout pipe openings near the room floor. It has a lower temperature as the air in the room itself so that it develops a "cold lake" of air in the room. Near to heaters the air will become warmer and rises up to the ceiling, where the used air is taken out.
This principle of ventilation is suitable for ventilation and cooling but not for heating!
So for the heat recovery system it is not useful, but it has the benefit that the hole used air is taken out of the room and is not mixed with the fresh air coming in.
b. mixing system
This is the mostly used principle because it is suitable for ventilation, cooling and heating. The incoming air is exhausted into the apartment on specialized points in the supply zone (explained later on) and mixes up with the room air. On other places in the apartment the air is taken out. The problem is that there is always a mixture of fresh and used air and the quality is not as good as it is with the displacement system, but this can be balanced out through a higher air changing amount.
2. Zones in the apartment
To have an optimal function of the mechanical ventilation it is important to divide the apartment in different Zones.
These are zones that are supplied with fresh air like living area, sleeping rooms and the rooms of the children.
Zones were the exhausted air is taken out are kitchen and bathrooms.
Hallways and sometimes dining rooms are zones in between to exchange the air from the air supported zone to the zone were the air is taken out.
3. Arrangement of the in- and outlets
The inlet of the air should be placed to avoid draught and to make sure that the air is properly spread out. It is important to have the whole volume of air in the apartment taken out to prevent the air from becoming bad quality.
Velocities of more than 15 m/s should be avoided to prevent the feeling of draught!
4. Air amount change
"Overall, the Building Regulations require that the air change in any habitable room and the house as a whole is minimum 0.5 per hour. At a room height of 2.3 m this air change corresponds to an inflow of outdoor air of 0,32 l/s per m² net floor area."
(from: "SBI direction 189" - page 82)
The air amounts taken out should be:
Bath 15 l/s
Kitchen 20 l/s (> 40 l/s extra extraction demand-contolled)
The same amount has to be supplied into the apartment. 35 l/s
Laundry 20 l/s mostly in the basement in multistory houses!
Continuous ventilation throughout night and day should be supplied. And an extra extraction through the cooker hood which can be switched on is favorable, because of the more pollution during cooking process.
5. Things considered in technical planning
In the technical planning there are different things that have to be considered by the architect previous to the extra precise plan that is made by a ventilation technician (mostly the producer company of the ventilation system).
dimensions of duct size and service room
The architect has to make enough room in the shaft to fit the pipes in.
The placement of the ducts has to be made according to the use of the building and the fire divisions. Materials should not be contribute to fire and smoke.
Dimensions of main ducts are:
ø 160 mm max. 67 l/s (242 m³/h)
ø 200 mm max. 121 l/s (436 m³/h)
ø 250 mm max. 218 l/s (785 m³/h)
ø 315 mm max. 401 l/s (1443 m³/h)
ø 400 mm max. 751 l/s (2704 m³/h)
ø 500 mm max. 1355 l/s (4847 m³/h)
There is also a space for the service room of the ventilation system to consider.
The space for the service room for ventilation should be twice the length of the ventilation unit and 2,5 times the width of the unit!
The architect has to decide if it will be on the roof or in the basement. Due to fire issues it is better to have it on the roof, but the weight of the system has then to be included in the load calculations.
The ventilation system can spread fire and smoke throughout the multistory building. That is the reason why it is extremely important to make sure that the fire demands are abided.
prevent fire and smoke spreading through the ventilation system with fire related seperations
prevent risk of fires beginning, caused by the components of ventilation system
reduce risk that ventilation system contribute to fire development
Fresh air intake and exhaust has to be placed that the risk of fire spreading between several fire-related units in the same house as well as to the neighbor buildings or external stores are not increased.
Smoke dampers on fresh air intake are required if extraction and inlet are close together or not the same fire compartments.
The materials used should not contribute to fire and smoke.
The ventilation service room has to be an own fire compartment as well as the main ventilation ducts. The service room shall only be used for ventilation and technical purposes and not as storage. There can be more independent systems without further fire protection. If the ventilation system is placed in the free, it has to be minimum 2,5 m away from the property lines and it has to be made sure that fire spread through the facades is prevented.
Ventilation system must not pass fire walls class (R)EI 120 A2 - s1, d0
A smoke ventilated system should be used:
It means that the Smoke in the system is conducted away to the free in a safe way.
There is also the possibility to use a ventilation system which can take the smoke out of the apartment through both exhaust and inlet pipes in case of a fire.
demands on sound impact
The architect has to make sure that the ventilation system is sound improved and that he chooses a system which is not making too much noise.
Sound demands are:
In habitable rooms (and shafts) 30dB (A)
In the service room (and on outlets to the surroundings) 40 dB (A)
Due to sound reasons there cannot be more than one branch out to the dwelling on one floor.
It is important for the comfort of the habitants that the sound level of the ventilation is kept as low as possible.
Laws and standards related
By planning the ventilation system several rules has to be followed like the newest building regulations (BR 08), DS 447, DS 428 and DS 452!
insulation of the system
Ducts have to be insulated to minimize the heat loss from the duct system and prevent condensate.
(example of insulation from the document domestic insulation from "via uc" > Fronter)
If the ventilation machine is placed on the roof or in an unheated service room the unit itself has to be insulated additional to the normal system insulation.
Something very important in the architectural planning is that an airtight building envelope is required for efficient heat recovery! The architect and the contractor are responsible for this.
positive and negative aspects and experiences
Important things for the occupants on the ventilation with heat recovery are:
good control system, easy maintenance work, low noise level and good indoor climate (including moisture)
it shouldn't be easy to turn off because the occupants forget to switch it on a gain and the air get's bad
need for automatic, operation-stable and airtight bypass; should be controlled based on a well chosen outdoor temperature or be permanently activated in summertime!
System should be controlled and the energy savings and electricity amounts needed should be measured to find out problems in the system or with the machines which are not obviously seen.
It is also important that the ventilation system is monitored and the great amount of service has to be considered as well as the costs for this has to be thought of along with the operation costs.
Most important advantages of the ventilation system:
optimal dehumidification prevents damages on the building (e.g. through mould fungus)
filters keep dust, pollen, insects, smell, etc. out because of filtering of the air
health and comfort because of fresh and pure air with the right amount of humidity and no noise problems
no house dust mites because of lower humidity
no cold air feeling and draught as when windows opened up for ventilation
lower energy costs due to the heat recovery
There are so many products and producers that it is important to compare the individual products and talk to the producers to find the best one for the own project and the special building.
V. List of references
E-books from Hochschule Augsburg (home university)
Springer Verlag (springerlink)
Chapter heat recovery from the book
Chapter ventilation from the book
www.passiv.de > Passivhaus Institut Darmstadt
MERA Multi-storey Building - Finnish Passive House?
Documents from the internet
Ventilation and health in non-industrial indoor environments: report from a European Multidisciplinary Scientific Consensus Meeting (EUROVEN)
Indoor Air 2002; 12: 113-128
Printed in Denmark. All rights reserved
Copyright _ Blackwell Munksgaard 2002
Documents from the university (via university college - from fronter)
Domestic ventilation (Jens Peder Pedersen, Vitus Bering Denmark)
Ventilation and indoor climat (Jens Peder Pedersen, Via University Collage)
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