Follow the crew at Compound as they build an energy efficient home with passive house principles. In this 4 part series we will go into minute detail on what it takes to build a house like this in New Zealand. Treated Floor Area : 146.9m2 Heating Demand kWh (m2a) : 23.9 Heating Load W/m2 : 12.6 Frequency of overheating (+25 ‘c) % : 1 Airtightness: 0.21 ACH In this episode we cover our mechanical ventilation heat recovery, Solar energy & Tesla battery. We talk about the considerations when striving for the Passive House standard. How does it feel? What its like to live in a Passive House Low Energy Building and does the level of comfort match what was predicted in the PHPP modelling.
See previous 3 episodes: Watch Us Build a Passive House – Episodes 1 to 3.
YouTube Video Transcript:
Since the blower test, we’ve completed the house and, you know, we’ve done our isolation, final layer, linings, paint, joinery, and now we’ve finished the final piece of the puzzle, and that is the mechanical ventilation system. So we know we’ve got a certain amount of cubic meters in the house, now we’ve had the blower test, we’ve got 0.2, so we have a very, very little amount of air leaking in this house. Passive house standard is 0.6, so the increase in performance huge there, and we can easily manage that air in this environment because it’s so airtight – it’s a mechanical ventilation system and can just work efficiently 24 hours a day in the background just supplying and extracting that air, filtering it. Supply, extract, and you just turn it on and let it do its job.
A normal house with openable windows – as you open a window on one side and on the other side, and the air passes all the way through and that’s kind of what happens, so in a high-performance house that’s airtight like a passive house, we have to do this mechanically. So we inject fresh air into bedrooms and into the living rooms, effectively that becomes a positive pressure zone, and that spills out into your hallways, and it travels down onto your wet rooms, which is your bathrooms, your laundry, your kitchen, and they are negative pressure zones. So we’re drawing air out of those locations all of the time, so that’s 24 hours a day, seven days a week, those areas become negative pressure so any moisture in those locations – that’s contained in those locations and also removed. So the ventilation unit will extract from your wet rooms, but it’ll bring all of that back to the unit. It’ll recover or strip the heat out of that, it’ll send the heat across to the incoming air supply, but the moisture just passes outside but just disappears.
So I’m commissioning this MVHR unit, so right now, I’m going around and measuring the air speeds, so I’m just getting an average reading what’s coming out of every single extract and intake.
I’m going to read it on the master bedroom over here, and the master bedroom came through at 16 on my reading, and right here, according to Steve, we’re looking to achieve 30, and then we’ll carry this out across the whole house, getting the readings of what we got, have what we have now, and then we will adjust each dropper to achieve the right reading, right 19?
If we look at all of the living spaces and the air volumes being injected into those spaces versus the wet rooms and all of the return air volumes added together, those two total bottom-line values must be the same. And what that means is that we’re not pressurizing the house and we’re not depressurizing the house. But also, what’s happening with the heat exchanger core is that the same volume of air is passing through the heat exchanger core on both sides, and that gives us our maximum heat recovery efficiency.
You know, doing higher levels of air tightness and higher levels of insulation, high-performance windows for that matter, those are pillars. And one of the pillars is also your heat recovery ventilation. So they all work together to get this high level of comfort that we’re desiring. So you can do one thing or the other, but really what you need to do is do all of them together.
We’re thinking about the insulation being continuous and thermal-bridge free from when we design it all the way through to when we complete the structure. And that goes the same for the air tightness, and that goes the same throughout the whole building process. So as you can see, if we don’t do this correctly, that’s not going to work as well. Or, if so, if we don’t do the air tightness and Vapor Barrier correctly, insulation over time will deteriorate. And if the home isn’t airtight, the mechanical ventilation isn’t going to work efficiently. So all of those five principles, all complementing each other, one’s not working solely like on its own. So you can see this idea of continuity between the principles and passive house standard. It also applies in the planning and design phase with the relationships between each party; you’ve got your builder, you’ve got the owner, the architect, those parties complement each other at the initial design phase.
How’s the design going to reach the standard or be energy efficient? How’s it going to be built? How are we going to get the mechanical ventilation services throughout the home? Say, for example, here at Moonlight, it’s a two-story, and we’ve got to get all our ductwork into each room through a mid-floor – so that’s where we use the posi strut floor. So without the builder being on board early, the likelihood of reaching the standards is at risk – as well as, you know, without a certified designer using PHPP, you’re probably going to miss some of those key areas.
So a lot of people ask, “so why did you use posi strut flooring and why do we recommend it to clients?” It is, you know, known as a bit more of an expensive floor joist system. If you look up there and see what we’ve been able to achieve, and yeah, much easier our sub trades job is with this flooring system. They’re not drilling any holes, it’s easy to run their cables, their pipes, and just knowing that I don’t need to worry about my subbies drilling holes anywhere because there is endless opportunity for them to run all their services. The floor system, the supply of posi strut might be a little bit more expensive, but your cost savings for your builder and project management is huge because, you know, I’m not having to worry about where these ducks and plumbing and supplies and where our subbies drill holes is going – I just know that they have the room to do it all, so the cost savings for me is in your builders project management.
Having a builder involved in the process as early as possible was a really good thing from a cost perspective. The later in the process and the design process that you make changes or even in the construction process, the more expensive it’s going to be, so just naturally through administration costs and rework and things like that. So having a builder involved in the process early can identify details within the drawings where it might not be possible, like from a buildability perspective, and then also find efficiencies and designs for building. The upfront cost is very small to get a builder involved in a few design meetings, and it can have a big impact on “like a compounding effect” on the price at the end of the job, so that’s highly beneficial.
So you can see how continuity is an idea that runs through throughout building to the passive house standard – from start to finish, just from planning to the design to execution to completion, and then it continues on afterward once you’re living in the house and you start to see how the home is working to its modeling. You know, when in winter, you’re getting that low sun, you still know this home, we still have a heating demand of 21 kilowatt hours per square meter, so we still have some heating, and then you’re seeing how that modeling works and how those windows bring in that low sun into the house and then warm up the space for a limited time in winter, but then, okay, so I need to time my heating on to cater to my heating demand in those shaded hours, and then you just work out slowly how you work out the more efficient way to be living in the home.
We installed a solar system with a Tesla battery on the home. So, on this property, we’ve got 14 Hyundai 390 watt panels, and obviously, it’s a really high-performance home. We’ve looked at some of the modelling, and we’ve created our own modelling about its energy demand. Typical homes in New Zealand, I suppose, in Queenstown, we’re installing probably slightly higher than that, kind of 18 to 24 panels with a battery set up. But in this situation, the demand in the property is quite low because it’s so efficient, and so we’ve started off with a smaller array that we’re confident will cover the demand and have ample access to charge that battery in the day.
We model every home, and from plans, if we can get a hold of them, especially with a new build, it’s nice and simple, and that model takes into account the angle to North, pitch of the roof, weather data from the local area, and any shading from any trees, and we can create really accurate data of how many kilowatts and the system will produce annually on average per month and average per day as well, and so it’s really accurate. We’re expecting this system to cover kind of 70 plus percentage of demand of the home, and so that’s something around six to eight thousand kilowatt hours a year, and the net result for the homeowner should be a dramatically reduced bill. I imagine their power will be something like 20 to 30 percent of what it would be without solar and a battery.
So here we have the connection to the Tesla Gateway, you’re showing us live data from the solar production, the loading in the house, and the state of charge of the power wall. This is showing right now that the solar is powering everything inside the house, any excess has been directed into the power wall to charge it. Yeah, we’re on a sunny day, we’re producing, in winter short days, but suddenly we’re producing 10 kilowatts, and the battery can store at 13 and a half. So you know, in winter, we can charge that battery, use the solar to kind of take care of any of our energy small energy needs in the middle of the day, and then obviously at night when everyone gets home, we use that battery.
Another thing we’re actually incorporating is on our energy contract, but we get free power for a time period, and we just put our heating on and charge our battery. Being a passive house and being so airtight and energy efficient, that heat just doesn’t evaporate once the heating’s off, so yeah, it’s a bit of a win-win at the moment.
So we’ve got a 24-hour period here: midnight to midnight. Above the line is demand, the battery discharging, or solar production. I’ve got three colours: blue for the battery, yellow for the solar, and red for grid.
In the early morning, the battery’s discharging and meeting the demand of the household up until the grid tapped out a little bit – you can see this red spike here, the demand at that moment in time is higher than the battery can discharge, and so it’s working in combination. About nine o’clock in the morning, the sun’s come up, and the solar has had enough power to cover the loads in the home, and so it’s reversed, and the battery here has started charging up again.
“In the later afternoon, once the battery’s got up to 100%, because it’s grid-tied solar, then exports to the grid and you get paid a small amount from your energy retailer – a little bit of extra help to cover the return on investment. The reverse happens when the sun sets; batteries discharging again. A couple of periods where the grid’s helped out again; demand at that period of time has been a little bit higher than the peak output of the battery, and then at nine o’clock here, time-based controllers has happened so the battery knows, “Right, I’ve got free power, I’ll charge from the grid again, but it’ll also cover the load in the home.”
So, in a 24-hour period, we’ve taken a little bit of grid power here in the early morning, probably with breakfast. A little bit of grid power here, well probably when we’re having dinner, but in effect off-grid for 23 hours of the day, something like that, and then with a cost to the client of probably net zero. A little bit of cost from drawing the grid here and here, but have exported some power here so probably dollar value about a zero.
So just stoked on the performance. It’s better than I thought, and also I’m stoked on like what we achieved in the design and how we fell short of passive house, and we have a small heating demand winter, but that’s already very small, like $100 a month including it’s a fully electric house. And we have a very, very low one percent heating requirement in summer, so I’m looking forward to seeing how that goes. I’m just stoked on the comfort, performance. The modelling is accurate, and yeah, like it’s the numbers don’t lie, so yeah, it’s been pretty awesome to live in it and experience it, and it’s freezing outside, you open that door and it’s just like, and you just don’t want to leave.
From what we’ve learned, it’s worth striving for that passive house principle and incorporating those five principles into your build. You don’t necessarily have to achieve the standard, but using all of those five things and modelling your home is going to make a huge difference to your comfort and a huge difference to the environment and a huge difference to the longevity of the building, and if you’re thinking of these things from the start, it’s going to pay off in the comfort in the long run. So, yeah, even if you don’t get to the passive house standard, you’re going to have a home that is five times better than most houses in New Zealand.”
