The following chapter starts with a brief discussion on lighting. Good lighting principles are so often forgotten it seems, with horrible glaring pinpoints of light, but are as crucial in MDH as in any house. My knowledge around lighting has been mostly gained through years of experience, and then honed in the design of bars I have frequented around the world, where good hospitallers understand the crucial difference between the three types of light.
This chapter may be the most useful of all to architects and architectural designers, given that it has had the extensive input of three experts in their field. We have an extensive guide from Peter Downey from HSCNZ in Auckland who has very helpfully set down a comprehensive list of do’s and don’ts around plumbing and drainage principles. Get these right and the building consent should sail through. We then have the benefit of expertise around ventilation, heating and cooling from Patrick Arnold, Director of E-Cubed in Wellington, with excellent breadth of experience in the field. Then finally we have Simon Hoyle from mechanical ventilation experts Ventüer, giving a manufacturer’s viewpoint on ventilation as well – a different approach perhaps, but identical in the understanding that this is a crucially important area for MDH in New Zealand. There is a lot in this chapter, but no pictures.
Many architects will be used to doing their own lighting plans, often sprinkled with recessed downlights in the ceiling. While it is good that we have moved on from halogen bulbs (nasty!) and onto LED (much better), we also need to design lighting differently in MDH from the way we do in a stand-alone home. Let’s recap on lighting generally.
For any room, three lighting layers are necessary: ambient lighting, accent lighting, and task lighting. Task lighting remains the same in MDH, with LED strip lights above kitchen benches, in bathrooms, or desk/ table lamps for reading/working etc. Accent lighting is to create a focus on the wall (or floor) and is often via directional spotlights mounted on the ceiling or the wall. These accent lights can be much brighter than the ambient lighting and can create a sense of drama to a room, providing contrasts and interest.
It is the layer of ambient (background) lighting that holds the most potential for change in MDH, as recessed downlights are not really a good fit for ITF. The penetration of any ITF built-up system by cutting holes into the acoustic and fire-resisting underside for downlights is a real problem, so avoid this if possible. Recessed downlights do provide a sprinkle of light but are never really very good ambient sources, as their light output is solely downwards which leaves the ceiling dark, as well as ruining the integrity of the fire resistance and creating an acoustic path for noise to trace through.
Install pendant lights on the ceiling (minimal holes for wiring) or up-lighters set onto the walls or mounted on floor lamps, bouncing light off the ceiling. Pendant lights can be very simple and affordable, with the option of the client selecting their own choice of shade, and a pendant light can provide both up-lighting and down-lighting at the same time.
With wall lights, the lamp size may need to be bigger as the light has further to go (upwards to bounce off the ceiling and then down to illuminate the table), but the ambient glow from the entire ceiling being lit provides a much nicer feeling in the room, and no annoying bright pinpoints of light against a grey ceiling plane.
Are they necessary? Ask yourself this one question: where do the majority of fire-related fatalities occur? It’s a simple answer. Not at work, where we are awake and are mobile, and where sprinklers are compulsory in multi-storey office buildings. Smoke and fire-related incidents and fatalities occur mainly at home, at night, typically from a fire or heater, from faulty wiring or from smoking in bed. Our senses are dulled when asleep, so we are at our most vulnerable and cannot smell the fire or hear the flames till it is too late. Fire-rated construction is one important answer, while the other is to install smoke detectors, alarm systems and best of all, sprinklers.
Residential sprinkler systems are rare in New Zealand houses due to their perceived extra cost, but they are never cheaper to install than at the time of construction, when the base structure is easily accessible. Multi-unit residential buildings (MURBs) should have sprinkler systems installed if they are in the form of apartments and especially if they are over three storeys high. They need to be designed by a professional, but a good architect will be thinking about their placement from day one. Plan for routes for pipework to be placed so that surface mounting and multiple penetrations are not necessary through beams or slabs. With an average spread radius of 2m for each sprinkler head you can work on a pattern of sprinklers every 4m in each direction to every room. On a large building these will be the standard steel sprinkler pipes you see in commercial buildings, while for a small project like a two or three storey terraced house there are lower-spec solutions made from thermally-resistant plastic piping. Specify pop-down sprinkler heads if you can, for a very discreet and almost unnoticeable solution.
Plumbing and Drainage
This sub-chapter is authored by Peter Downey of HSCNZ
Advice from an experienced industry insider. A few things to consider!
Ownership title structure
- Ownership structure affects the type of drainage system needed: fee simple, unit title, or leasehold
- Fee simple requires each lot to be serviced by a public drain.
- Public drains don’t require easements.
- Private drains crossing an adjacent private lot need an easement (and subsequently negotiation with the current owner).
- For a unit title with a body corporation in place, common private drainage can be extended to service each title.
- Leasehold is similar to unit title.
- The above advice should be checked with a surveyor.
Cold water and fresh water
- If fee simple ownership, ensure a separate public water meter for each lot.
- Unit title and leasehold can have private water meters downstream of the public water meter. Ensure these meters can be easily read. Battery operated, remote read, pulse capable meters are available.
- Water pressure requirements. A mains pressure of around minimum 400 to 500kPa maximum is expected by most purchasers these days.
- Don’t run water pipes serving Apartment A through Apartment B (the adjacent apartment). This is a biggie. Just don’t do it.
- Don’t set plumbing fixtures on fire separation walls. Instead, build a wall-on-a-wall, and put the services in there. This reduces the fire rating.
- Make sure all valves are easily accessible.
- Use plastic pipes internally, as they generate less sound.
- Keep the pipes separated from the structure by rubber insulation, to reduce noise transmission.
- Public water meters are public property and thus belong on public property – usually they are located just outside the boundary on the footpath. Each fee simple house needs its own separate public water meter and a private run of pipe to the dwelling entry. The pipe should not carry over onto someone else’s property.
- In unit title situations, the private water meter can go anywhere, as long as it’s accessible for reading and repair. Most private meters in multi-unit dwellings these days are battery-operated and are read remotely. See the page on water metering at waterware.co.nz.
- Probably the most important thing is to have the apartment water shut-off valve visible to the owner. Nobody cares until a flex-service pipe on a faucet blows, then everybody is in a hurry to find the shut off valve. But no one can ever remember seeing it!
- Site the hot water generating unit sensibly. It and its valves need regular servicing. The manufacturer requires the owner to ease expansion valves every six months. Don’t build the cylinder into a corner and cover it with a heavy cover with 88 screws in it.
- Make sure the hot water cylinder (HWC) cupboard can fit the size of the cylinder and its pipework. Allow space for servicing the pipes.
- Don’t put an external gas unit so high that it can’t be reached for servicing.
- Don’t put the cylinder too far away from the fixtures it serves, especially the kitchen sink.
- Put another 15 litre cylinder under the kitchen sink if it’s too far from the main cylinder.
- Dead-leg HWC systems don’t require pipe lagging so long as the pipes are inside the thermal envelope.
- Consider the TPR and CWEX drains to the cylinder in terms of their final outfall.
- The old Housing New Zealand standard was a 135 litre cylinder for a single bedroom dwelling, and 180 litre for anything bigger. That’s still a pretty good yardstick. But the new 180 litre is a 250 litre in any upmarket house.
- Provide sufficient vertical passage as every graded offset generates noise. This is particularly difficult in townhouse type construction at midfloors.
- Provide enough depth for the pipe diameter and its associated falls.
- Consider fixture overflow. Floor waste gullies are not the only way to achieve compliance with E3. Use internal overflows in fixtures and/or dry type floor waste system.
- Consider terminus location of main vent pipe. It must be 3m away from any openable window or trafficable deck.
- Consider acoustics treatment to pipes. There is nothing necessary to meet NZBC, but to achieve today’s expectations, wrap horizontal pipes over noise sensitive areas, or use special acoustic pipework.
- Vertical pipes don’t require additional treatment if a builder’s duct is constructed properly and the pipes go straight down without bends.
- If fee simple, provide a public connection to each lot.
- Consider the slab construction. Rib-raft is particularly troublesome for pipework.
- Coordination with structural elements.
- Identify outfall.
- Ensure sufficient fall to outfall.
- Provide each building with an overflow relief gully trap (ORGT), the grate of which must be at minimum distance of 150mm below FFL.
- Provide adequate maintenance access.
- Consider 1:60 as the ‘normal’ pipe gradient.
- A floor waste is a great thing, so long as water flows to it. This is such a simple concept but ignored by many. The preference these days is for large coverage floor tiles which are hard to lay at falls, so they are laid flat. This means that any floor waste grate sitting in this floor will probably never see water. Funnily enough, water flows out the door before it flows down the FW grate. Surprise, surprise!
- To counter this, a threshold tile is a good idea. Say 75mm wide at the door threshold and sitting say 3mm above the area surrounding. But even this logical addition is too ugly for many, so they choose to add nothing. Be warned – the bathroom will flood out onto the carpet.
- A dry floor waste system is when a separate system of pipes carries overflow water throughout the building. It runs from the small 40mm diameter grate in the kitchen, bathroom, laundry (or whatever else needs a floor drain), with no water trap, to discharge over a gully trap, or extend through the wall and terminates with a vermin flap. The good thing about them is that they are completely separate from the sanitary system, so a blockage in the sanitary system is successfully dealt with.
- Dry floor wastes are described in G13/AS1 Clause 3.4 Floor outlets (figure 3). There is no water trap, so no water seal to evaporate away and consequently, they are sometimes a sound/smell conduit between apartments. Do not connect directly to the main sewer.
Storm water drainage
- If fee simple, provide public connection to each lot.
- Consider public overland flow path and maintain.
- Consider the slab construction. Rib-raft is particularly troublesome for pipework.
- Coordination with structural elements.
- Identify outfall point and ensure sufficient fall to outfall.
- Provide adequate maintenance access.
- Consider 1:100 as the ‘normal’ pipe gradient.
Roof, balcony, and deck drains
- If fee simple, separate out the catchment areas – there should be no shared areas.
- Serve each catchment with its own downpipe. Fix this downpipe entirely within the title it’s serving.
- Every downpipe in an internal gutter must have its own associated overflow pipe. This overflow must be the same cross-sectional area as the downpipe it serves.
- Ensure the overflow is set at the correct height to discharge overflowing water, well before that water builds-up and enters the building.
- Each balcony/deck MUST have either: TWO outlets – or ONE outlet and ONE overflow.
- The overflow should be visible when in operation.
- Get the set-down at the level-entry right.
- Drain the level-entry drain to the correct outfall.
- Make sure the balustrade fixing does not compromise the waterproofing.
- Gas meters are ugly, particularly public ones. Make sure they are set near the very front of the allotment and provide an accessible, vented, architectural alcove to house and conceal them.
- Gas pipes can go unvented in most locations these days, as long as the joints are welded, or at least have a fully-compressed type joint, with no mechanical screwed manipulation used to make the joint.
- Generally, gas meters need venting.
Heating, cooling and ventilation
This sub-chapter is authored by Patrick Arnold of eCubed
Heating and cooling – Passive design
The best heating system to design into the building is to design out the need for heating through sensible passive design. The inventors of cheap heating systems and heat pumps (remember that in almost every other country, what we in New Zealand call a ‘heat pump’ is called an air conditioner) have a lot to answer for. Before an efficient and reliable source of heating was available buildings were designed passively out of necessity. Now however, designers are able to paper over creaking designs with efficient heating equipment. A ducted heat pump will take the fresh outside air and bring it inside before heating or cooling it, but most New Zealanders have non-ducted heat pumps, that just recirculate the existing internal air.
There are a myriad of good design guides available for designers to refer to, however, the general principles are:
- Orient the house and arrange the windows to make the best use of the sun (too many houses are sited so that first and foremost the garage is facing the road and then the living areas arranged from there).
- Insulate, insulate, insulate. And of course, ventilate, ventilate ventilate.
- Once a building is well insulated then thermal mass becomes important, even an exposed concrete slab can make a significant difference to both the heating and keeping a room cool in summer.
- Once well insulated, take care to avoid overheating; external shading will be needed on north and west-facing windows, along with some means for the occupants to securely ventilate the house during the day (when they may not be home).
The three traditional pillars of passive design for residential buildings are glass, mass and insulation, with airtightness a reasonably new (to New Zealand) addition. A good balance of all these aspects will result in a low energy house. In most parts of the country it is possible to design a house which should require no heating (except the North Island Central Plateau, and perhaps the lower half of the South Island).
A designer wishing to satisfy themselves or their client that this is the case may struggle, as heating is ingrained in our psyche, however tools such as The Passive House Planning Package design guides (or PHPP) or perhaps on larger developments, computer simulation from a sustainability consultant or engineer can be used to validate and optimise the design to minimise heating requirements, while ensuring that overheating is within acceptable limits. This is an important aspect to check – there is evidence from overseas where increases in insulation levels have resulted in significant overheating in not-too-dissimilar climates to New Zealand.
The fundamental principle is to have the building fabric do the heavy lifting in terms of providing acceptable and healthy internal conditions, and only provide active systems once the fabric has been optimised. One of the prime purposes of any active mechanical ventilation system is to control the moisture in the building. As an indication on how far away we are from American standards of air conditioning, while many in New Zealand may use a dehumidifier, in the USA they require humidifiers to add water back into their internal air.
System types and selection
Once a need for heating has been identified, the trick is then to select an appropriate heating system for the building. This will depend on the design of the building and the other systems within it. Some general approaches are:
- If a building has been designed with natural ventilation or high air change rates, then a radiant system should be used so the warmed air doesn’t disappear out the windows.
- Ideally the response time of the heating system should match or be faster than the thermal response of the building.
- The size of the system (measured in wattage) should be appropriate for the dwelling or room.
- Any heating should be thermostatically controlled and include timers to reduce energy wastage.
Sizing a heater (or air conditioner for cooling) depends on the level of insulation, the amount of solar and internal heat gains expected, and the climate the house is located in. On a reasonably-sized development there may be a services engineer who can carry out sizing calculations for heating, or alternatively the installing contractor can select appropriately-sized equipment.
A rather old, but easy-to-remember rule of thumb is that heating systems should be sized at 100W/m² of conditioned floor area, however, a well-insulated building with outdoor air provided via a heat exchanger will have a much lower heating load. In a well-designed house some rooms might only need a couple hundred watts of heating, which is about as small as heaters get. It may actually be better in the long run to alter the design of the building to reduce the heating load completely.
World Health Organisation (WHO) guidelines recommend temperatures for the home should range between 18°C and 24°C for a comfortable and healthy home environment, but notes that temperatures below 16°C with high humidity increase the chance of respiratory diseases and below 12°C are a real health risk to the sick, elderly, and pre-school children. University of Otago research indicates that New Zealand’s considerably lower indoor temperatures are doing considerable damage to the health of our most vulnerable communities (Howden-Chapman, Home Truths, 2015). On the other hand, escaped refrigerants continue to do extraordinary damage to the ozone layer – a single kilogram of CFC gases can destroy 70 tonnes of ozone (Wilson, After Cooling, 2021), so heat pumps are not the answer for everything either.
Where loads are low, smaller electric radiators can be used. This is about as simple as a heater gets and is therefore the cheapest option. Radiators can combine well with natural ventilation as they are a fast response system and don’t immediately heat the air. However, this creates a significant disadvantage in that the occupants of the room will still be breathing colder (and therefore damp) air, which can contribute to poor respiratory health. For dwellings where there is little chance of the windows being open during the winter and/or with balanced heat recovery, small wall-mounted convective heaters can be used.
Underfloor heating is a slow-response system which makes benefit of the thermal mass of a concrete slab. It should not be used in glassy buildings or even lightweight buildings without high levels of insulation. If the building warms up quickly naturally (on a sunny winter’s day for example) the floor will still be part-way through its own warm-up cycle, leading to an overshoot and overheating in the afternoon. Ideally a heated floor should be left at a constant, moderate temperature and the occupants taught to resist the urge to play with the thermostat. On multi-unit developments several dwellings could be served by a central plant room – though this might then raise the need for some kind of metering strategy to apportion running costs between the tenants.
The slab can be heated using water or electric mats. While more expensive up front, hot water is by far the most efficient option and gives excellent controllability. These days the most common way to heat the water is through an air-to-water heat pump. This would have to sit outside in a spot where the noise won’t bother anyone, is well ventilated, and it gets washed by the rain (nearly every town in New Zealand is prone to salt-laden air, which quickly corrodes mechanical equipment).
Of course, the typical heating solution these days is a heat pump, or split air conditioner. This is made up of an indoor unit, which normally hangs on the wall inside (though concealed versions are available), split from an outdoor unit which again needs some careful placement outside. A heat pump does just that – sources heat from the colder exterior and pumps it to the warm interior in the opposite direction to which the heat naturally goes (or vice versa when in cooling mode). This process is actually very efficient as the ‘source’ heat outside the building is free and the homeowner only has to pay for the power to run the pump. Heat pumps warm or cool the air in the room quickly, and when in cooling mode can carry out a degree of dehumidification. It is important to remember that non-ducted domestic heat pumps do not provide any outdoor air, they simply recirculate. They also only tend to include coarse filters.
Most people are familiar with the heat pump controllers, which can set the temperature and fan speed. It can be a good idea to get the controller ‘locked’ so that the possible temperature range is limited. Similarly, it is possible (depending on the make and model) to lock the outdoor so that it runs in heating mode only.
The unfortunate thing about heat pumps is they rely on refrigerant to transfer the heat from one place to another. Nearly all refrigerants have a high global warming potential (GWP), with the 1.5kg of refrigerant in a typical domestic heat pump being equivalent to around 1000kg of CO₂ – and that’s with R32, a modern, good (or less bad) refrigerant. Older refrigerants have higher GWPs and have typically been slated for phase-down under the Montreal and Kigali Protocols, which is another reason to avoid older or cheap heat pumps. New refrigerants are being produced constantly, so we hope that their GWP will come down, but in the meantime this aspect needs to be considered when examining overall carbon savings (for more reading on this, refer to Wilson, After Cooling, 2021).
Refrigerants can also potentially be flammable, or toxic, or act as asphyxiants, so the volume of refrigerant used in a system may be limited for a given room size. Again, an installer or consulting engineer are the best people to check this.
Generally speaking, the ventilation of a house comes in two forms; background ventilation, which is constant low-level turnover of air, and comfort ventilation, which is ventilation used to cool down a room or dwelling during summer. A well-ventilated home is not only ‘fresh’ but should also be drier, easier to heat, and therefore healthier for the occupants. Currently ventilation requirements are set for general life safety and measure carbon monoxide. They do not take into account occupant comfort and moisture loading or condensation control when establishing air changes. Base design includes mostly passive ventilation reliant on occupants, or active ventilation in the form of bathroom/kitchen fans.
These are most often occupant operated, but could be easily tied to humidity sensors, or CO₂ sensors. It would be good to identify the issues with so much being reliant on the occupants when the design can be done better. We need to do better
Traditional New Zealand houses have excellent levels of background ventilation – but for all the wrong reasons. The leaky timber construction, lack of insulation and building wrap means that air effectively passes through the walls, not to mention around windows and doors.
While obviously highly detrimental to energy efficiency and all attempts to keep the house warm, this infiltration means that the air in the building gets turned over regularly. This background ventilation helps to dry out the building, removing water vapour inside the house which is generated through cooking, bathing and laundry carried out inside, and drying out any rainwater which inevitably gets into the walls through cracks and gaps in the construction.
New houses are built with much more attention to weathertightness and air-sealing, which brings the opposite effects into play – while excellent for comfort and energy efficiency we now have to be deliberate about providing ventilation and can’t just rely on fortuitous (and completely uncontrolled) infiltration.
Just leaving the windows open will offer very high levels of outdoor air, though again the amount of air is hard to control and will only be whatever temperature and humidity the outdoor air is. Cold temperatures first thing on a frosty morning are not conducive to making one want to open a window! Furthermore, it’s often undesirable to leave a window open during the day for reasons of security, or the inevitability that it will start raining once you’re ten minutes from the house. This means that spaces don’t tend to get ventilated year- or day-round.
Best-practice is to provide mechanical ventilation using a heat recovery ventilation unit (often abbreviated to MHRV, though it does vary by the brand). It is important to realise that this is a different system to various air-transfer systems available on the market. The important parts and principles of an MHRV system are:
- It brings in ‘fresh’ air from outside, typically through a grille under the soffit or on an exterior wall, or through a roof cowl (some single-home domestic MHRV just draw air from the roof space, which is not fresh air).
- This air is ducted to the unit itself, and ideally filtered to remove pollutants. At the same time ‘stale’ extract air (sometimes, but not necessarily from the bathroom) is removed from the dwelling and ducted back to the MHRV unit.
- Within the unit are normally two fans (one for supply and one for extract) and a heat exchanger, where the cooler incoming air is passed alongside the warmer extract air, and the incoming air is pre-heated to a more comfortable temperature (the reverse occurs in summer, with the incoming air being cooled, but this is less effective). Modern units advertise recover efficiencies of up to 90%.
- The incoming and outgoing airstreams should be separated by the heat exchanger membrane so that only heat energy is transferred from one to the other, not pollutants.
- The pre-heated supply air is ducted from the unit throughout the house to the living areas.
- The exhaust air is vented to the exterior through either a grille or cowl, in a location well clear of the intake so the airflows do not short circuit.
There is a trade-off – in that the unit costs energy to run, and it should run continuously. However, in nearly every instance the cost to run the MHRV unit is outweighed by having a warmer, drier house to start with, before the need to heat it occurs. There are also health benefits in the constant background ventilation preventing mould growth, and removing VOCs from the indoor environmen
There are, however, some important design considerations, most particularly the need for ductwork throughout the house. Because the unit is only providing background levels of outdoor air these ducts do not have to be large, typically no more than 200mm diameter including the insulation, however, these still need to be worked into ceiling voids and over lintels, and between the floors in multi-storey units. Typically, designers make use of lowered ceilings over wardrobes or other joinery, bulkheads at the edge of rooms, and hide duct risers between floors in the corners of windows or hot water cupboards.
It is also important to make sure that all rooms being served by the MHRV system can ‘talk’ to each other in terms of ventilation. The outdoor air supplied to the living areas needs to be able to make its way to the extract point. This may mean extract grilles strategically placed throughout the house, or door undercuts.
The MHRV unit itself is normally small enough to conceal within a joinery unit, at the cost of a cupboard, however, the duct routes need to be as direct as possible. Remember there will be four ducts: intake, exhaust (from the unit to the exterior), supply, and return (from the rooms to the unit). Keeping the duct as straight and as large as possible will reduce not only the amount of energy the unit uses, but also the noise from the air flow.
Another factor in the amount of energy the unit uses is the level of filtration. The higher the grade of the filter, the greater the pressure drop on the intake (or more simplistically, the thicker the shake, the harder you have to suck on the straw). Various grades of filter are available, and unhelpfully there are several scales used to classify them. The minimum grade of filter which should be used is a MERV-13 (or you might still see the older code of F7).
Increasingly MHRVs are being supplied which include HEPA filtration. This is hospital grade and a step above that used in typical buildings, however, it is increasingly common due to current concerns around Covid-19 and other airborne infections. By definition a HEPA filter blocks 99.97% of particles 0.3 microns in size. A typical airborne water droplet carrying a nasty virus is around 1.0 microns. For comparison, a MERV-13 filter will catch 80% of these particles. While most Ministries of Health believe that MERV-13 filters are enough to minimise the spread of infectious aerosols, the only downside of using a HEPA filter is the higher pressure and therefore fan energy.
The last, but most important thing to consider with MHRV is the final install needs to be commissioned and balanced to ensure that the system is operating correctly. The airflow in each duct or at each grille of the system needs to be measured and checked against the design. This is an essential step in achieving a high performing system that does what is intended and achieves the positive benefits described above. This will require the services of a genuine mechanical services or commissioning contractor – it may be that the selected MHRV supplier will have recommended or even certified installers.
The ventilation system should be balanced. This ensures that as much air is brought into the home as is being extracted. If the system is out of balance then the remainder will be drawn in or out of the building through the building fabric in an uncontrolled way which, aside from being unfiltered and untampered, could potentially also bring water vapour into the building envelope. Balancing of the system can get difficult when additional ventilation systems are used for a specific purpose, for example kitchen or bathroom extracts. These are discussed on the next page.
The absolute minimum level of ventilation to provide for a house is extracting at the common sources of moisture: over the cooktop, in the bathrooms and possibly laundry. Removing moisture as it is generated, where it is generated, is the most effective and efficient way to prevent excess moisture entering the general areas of the house, the lungs of the occupants, and the depths of the building fabric. So, integrate your sensors into the design of the ventilation systems, so the occupant will always be drawn to remove moisture directly at source, in order to maintain a comfortable and healthy environment.
We are familiar with cooktop rangehoods, and specifiers will be familiar that some rangehoods are better than others. Some seem to make a lot of noise but generate little air flow – which is obviously best avoided. While easier to incorporate into a building and allowable by the current building regulations, recirculating rangehoods should also be avoided. Depending on the type of cooking and skills of the chef, the air the rangehood is dealing with can contain a lot of water, grease, smells, and possibly smoke. This needs to be ducted directly to the exterior to an external wall or even roof (which would then require a cowl) to reduce the pressure load on the fan. Unfortunately, the fans on rangehoods typically aren’t very powerful and they need all the help they can get. Keep any pipework as straight as possible and as short as possible, with 150mm diameter straight ducts far better than 100mm flexiduct.
Integrating the operation of a rangehood with an MHRV unit means balancing the extract air with the outdoor air supply. This is tricky as the MHRV unit needs to be oversized for day-to-day operation just to have the spare capacity to make up for the rangehood for the short time it’s used, plus most MHRV units are not designed to handle possibly greasy or smoky air. There is also the controls complication of having the two different systems (which have their own individual controllers which work perfectly well) somehow talk to each other.
Ideally the rangehood has its own supply or make up air, possibly through a second external grille with a damper which opens when the rangehood operates. The more expensive hood options can include their own supply air system.
Bathroom extracts should be located nearest the largest source of moisture, which is most likely the shower. These can be stand-alone fans for each bathroom, or even incorporated into an MHRV system. When using this approach care does need to be taken to specify a unit which can handle moisture-laden air. The heat exchanger of some makes/models of MHRV doesn’t like getting wet. When included as part of the MHRV system, remember that the air being extracted from the bathroom needs to come into that room from elsewhere in the house.
If using a stand-alone fan, make up air is still required, as is some type of switching. Often this is wired to come on with the light to ensure the users actually run the fan, however, some people find this annoying as they may not want the light coming on during the day, or may not need the fan when simply brushing their teeth late at night. The client will of course have a preference, but separate labelled switches are usually the most reliable option.
It may be easy to assume from the discussion so far that we aren’t allowed to have opening windows. Fortunately, this is not the case. New Zealand designers and homeowners both prefer large windows (by international standards) and doors which open out onto the deck or terrace for highly valued indoor- outdoor flow. We also have a lot more heat in our sun, even in winter, than most Northern Hemisphere countries in particular. This normally means that even in a well-designed dwelling with sensible levels of glazing and shading, there will be times when the occupants will seek cooling.
The background ventilation of an MHRV unit will go a long way to reducing the likelihood of overheating despite the relatively low air-volumes; the heat exchanger can take ‘coolth’ from the outgoing air and use it to cool down the incoming outdoor air (note that some models may simply have a bypass), but over time the indoor temperatures will start to creep up. High solar gains will also introduce so much energy into a space that it becomes very hard to counteract without higher air flows.
User-operated natural ventilation apertures (engineers’ talk for opening windows) can provide very high air change rates which provide comfort cooling during summer – within the boundaries of some fairly fundamental laws of physics: no matter how much air you push through a space, you will never get it cooler than the outside air temperature.
If you do have a design with a lot of thermal mass, that can be used to draw heat out of the air and keep the rooms cool – though the ventilation will have to continue once the temperatures have fallen to help reset the thermal mass for the next day (on commercial buildings this is called a night purge cycle). This might mean windows open at night, which then raises a security concern, although less so with upper- floor MDH.
As some of the scenarios suggest, the use of opening windows can become rather fickle, and the occupants will have to understand how best to use the windows to their advantage. Never underestimate the value of a bit of user training – there will inevitably be some responsibility on the homeowner to learn on the job! Where you can, remove the possibility for ventilation to be seen as an ‘option’ – make the building work, with or without the occupant. Small, cheap, discreet sensors can now easily be linked to the MHRV systems.
A common mechanical method of bringing in cooling which may suit some building types are ceiling fans. As we’re all familiar with, the air movement generated sets up a breeze, which then gives the sensation of cooling on the skin. Obviously, this doesn’t actually cool the air down, but the breeze means that people can tolerate higher temperatures while still feeling comfortable. The advantage of ceiling fans is that they don’t require the windows to be open, and therefore provide less interference with an MHRV system. Some care needs to be taken to ensure that the blades of the fan are not directly below a light, or else the fan will generate an unpleasant strobing effect. User controls are also important, with on/off and a speed controller normally preferred.
Ventilation and acoustics
An awkward acoustic problem to deal with is the issue of ducts and machine noise. Sound can travel along an air duct, so avoid having ducts connecting different rooms (obviously, ducts connecting different units are illegal as they could spread smoke and fire). A duct can also bring noise from the outside into
a dwelling, such as a car horn outside, the rumbling of a truck, or even people talking on the footpath passing by. It is important to consider stopping sound coming in as much as stopping sound getting out, and acoustic baffles can help solve that problem.
Ensure complete isolation between source and enclosure, and as much absorption of sound within the enclosure as possible. Mount motors on springs, or hang them from resilient fixings such as rubber mounting points. There is a reason why all those heat pump adverts on TV keep claiming that they are “very, very quiet” – that’s because noisy heat pumps can be very, very annoying, both to you and to your neighbour. Good siting of the unit outdoors is crucial to consider, to avoid the irritating constant hum. Muffle the sound at source, and isolate all potential vibration. Design in an enclosure for the outside heat pump so that it is both co-ordinated with your design and does not cause acoustic irritation to the occupant or their neighbours. For high sound reduction over a wide frequency range, the requirement is for high mass and low stiffness (Sharland, 1972).
Ventilation for MDH
This sub-chapter is authored by Simon Hoyle of Ventüer
Ventilation design for MDH
MDH ventilation systems require careful planning to ensure effectiveness. Prior to beginning your MDH ventilation design, there are three areas that need to have been decided upon and the relevant analysis carried out:
- Structural design methodology (how the mid floors, external walls, internal/inter-tenancy walls and roof will be constructed)
- Acoustic requirements
- Fire safety requirements
Identifying ventilation zones
Different rooms within the building will require different ventilation rates, dependent on their use. These rooms/zones may include the following categories:
- Living rooms
- Common areas such as lobbies
- Access paths such as lifts and stairwells
If utilising natural ventilation in your MDH project, the next step is to identify which zones must be mechanically ventilated (i.e. kitchens, bathrooms, rooms where the windows can’t be opened for acoustic reasons etc). The design and layout of the remaining zones that can be naturally ventilated should then be carefully considered. How can the building shape/location/orientation/design features be used to maximise the natural ventilation? Will this be adequate, or should mechanical ventilation be considered for these areas as well?
Ventilative cooling capitalises on the ‘free cooling’ provided by ventilation. A few considerations here:
- With the building design, how much cooling can be achieved via ventilation?
- How much ventilative cooling is practical and cost-effective, and how much cooling may need to be taken care of via a heat pump?
- How is the ventilation interacting with the insulation and interior environment regarding condensation and air quality?
Designing the system & selecting the system type
There are three primary types of MDH mechanical ventilation systems:
- Mechanical extract ventilation (MEV)
- Balanced pressure ventilation (BPV)
- Mechanical ventilation with heat recovery (MVHR)
Once you have selected your preferred ventilation system (which is typically driven by budget and climate zone), you can progress to the next stage in your design.
Laying out a ventilation system involves identifying the most appropriate location for the various components and equipment, and routing the required ductwork to link it all together.
Some of the considerations to take into account when doing this are:
- Proximity of intake and extract points to each other (NZS 4303 specifies minimum distances which vary dependent on airflow rate)
- Location of kitchen exhausts (don’t position these near washing lines or entrance doors)
- Position of façade penetrations relative to fire protected zones (if fire rated walls and spandrels can be avoided, fire dampers are not required thus reducing cost)
- Ensure duct runs are as short and as straight as possible, to minimise pressure loss and enable small fans to be used.
Selecting and sizing the equipment
Some of the equipment that needs to be selected and sized in a typical MDH project is as follows:
- Heat recovery units
- Fire dampers
The specification of this equipment often requires site-specific engineering and appropriate expert advice should be sought.
Detailing the system
Once the equipment is selected, the following details need to be included in the design documentation:
- Weathertightness details for exterior elements (cowls etc.)
- Duct support and bracing
- Fan locations
- Seismic restraints
- Make-up air location for extraction-only systems
- Maintenance/access points
Designing the system & product selection
All right, so you’re naturally ventilating some parts of your MDH project. What type of product is best suited for what you’re trying to do? There are many options, and no one-size-fits-all! Some product options are:
- Aluminium weather resistant louvres
- Double-glazed glass louvres
- Openable windows
- Trickle vents
For advice on the most appropriate natural ventilation device for your MDH application, contact a specialist ventilation product supplier such as Ventüer.
Detailing the system
Once you’ve selected and sized your natural ventilation equipment, the following details need to be considered and shown on your ventilation design:
- Weathertightness details showing how the products integrate into the façade
- Structural fixing details ensuring the system will comply with the site-specific wind loads
- Safety from falling – when the ventilation device acts as a barrier from falling (as many do), a set of specific engineering calculations may be required to demonstrate compliance with NZBC Clause F4
- Controls – if your preferred system is operable, will this be manually operable or linked to an automation system?
- Security – open ventilation devices can provide entrances for burglars and other threats. Ensure your design takes this into consideration.
- Prevention of insects, vermin and pollutants coming indoors. Bug screens (and – for certain systems – panel filters) should be considered to ensure occupant comfort is maintained when the natural ventilation systems are in operation.
At this point, pat yourself on your back – congratulations, your MDH ventilation system is designed.