Editor’s Note: This is one of a series of blogs by David Goodyear describing the construction of his new home in Flatrock, Newfoundland, the first in the province built to the Passive House standard. The first installment of the GBA blog series was titled An Introduction to the Flatrock Passive House. For a list of Goodyear’s earlier blogs on this site, see the “Related Articles” sidebar below; you’ll find his complete blog here.
The day-to-day operational costs of this building should be less than a code-built home. Lower energy use means lower energy bills. In principle this should lead to simpler mechanical heating systems. This aspect of Passive House design was always considered to be a way to tunnel through the cost barrier of all the extras, such as triple-glazed windows, high R-value walls, etc.
The choice for a heat source is often simple: a minisplit could provide all the heat required. However, my choices were influenced by many factors:
- Using photovoltaic panels provides a way to offset some of the source energy requirements of the building, but since net metering wasn’t allowed in the province at the time of my decision, future installation of PV seemed like a pipe dream.
- With electricity costs rising, using a locally available fuel source could offset some or most of the energy costs associated with being connected to the grid. This could be made possible by targeting the site demand required by heat and hot water.
- Having a heating source that uses minimal electrical energy would make heat and hot water available during periods of extended power outage.
- Use a fuel source that would dramatically decrease the source energy requirements of the building.
This all added up to “wood.” Wood is available locally, it can be burned to provide massive amounts of heat for both heating and hot water, and it can be used to offset source energy. Living in a province where wood burning is prevalent provides a natural choice.
The big problem with a wood stove is that they are too powerful. Finding a stove to meet small heating loads (i.e. less than 5 kW) is not easy. It also is challenging to find a stove with hydronic heating capabilities. The only wood-fired hydronic stove in Canada for a living room is the Walltherm. While firing, it dumps about 12.7 kW into heating water and only 2.2 kW into space heating. This requires a large thermal storage tank.
In my case I opted for the Logix24, which has a solar thermal exchanger built in.
Eventually I plan to use a Geyser-R (Nyle Systems) heat pump. That will help supplement hot water production in the summer by running the heat pump through the solar heat exchanger. There are many configuration options with a storage tank like this. It can be used for any type of radiant hydronic system including low temperature radiators, in-floor heat, etc. The connections on the tank also allow for supplementing electric elements.
Mechanical rooms are too small
I bought the stove and components seven months ago. I was happy when it was time to install the tank and start arranging the mechanical room. My HVAC contractor, Adam Rickert (Hot Water & Fresh Air Systems), has said multiple times, “Mechanical rooms are too small!” Finally, after months of planning, I believe him.
At only 7 feet square, it’s a pretty small room, mainly because the Logix24 tank is so big. The original layout of the mechanical room involved some assumptions that led to some problems. The main assumptions were about the size of the tank and the inputs on the tank. There was no way for the layout to work. It seemed fine during our design stage but once I received the tank, I realized that our plan should have been a little different.
The floor drain was not in the ideal position. The HRV would have to be relocated in the room. The well pump pipes are in the wrong place — the list goes on. This being said, I think we found a way to rearrange the room: The thermal store is now at the center of it all. This tank is commanding in every way! It uses almost one-quarter of the floor space in the room but it works!
The PAW pumping station is the mechanical guts of the system (see Image #2 below). It will push water from the tank to the stove and back to the return on the tank. The station includes a Grundfos Alpha low-energy pump. It draws between 8 and 45 watts, depending on the setting. I expect it will run somewhere in the middle, at between 30 and 35 watts.
The Viega distribution manifolds for the low-temperature panel radiators are also installed (see Image #3 below). The outdoor reset and mixing valve still need to be installed. We are expecting that the outdoor reset setting will be such that the water moving through the distribution system will be about 120°F in the dead of winter. The reset will adjust temperatures accordingly as exterior temperatures get warmer in the spring.
Moving the ERV incurs an energy penalty
The energy-recovery ventilator (the X24 ERV ECM by Venmar) looks like a great machine. It appears to be nicely built and has some decent ventilation features. It is a little on the large side, and because of its size it became a thorn in our initial layout plan. The initial plan was to place the ERV on the exterior wall directly below the Reversomatic dual intake/exhaust duct. Instead, it had to be moved almost 6 feet away from the initial position.
This uses about 6 feet of extra duct. This duct will be cold in the winter and warm in the summer, and therefore there is an energy penalty associated with moving the ERV to the interior of the mechanical room. The penalty is about 127 kWh per year, according to WUFI Passive. Adding another inch of insulation saves about 25 kWh annually, so it’s probably not worth the hassle.
As of now, the machine has been running just to help with the moisture load in the building. Once we are ready for diffusers to cap the supply and return ducts, the system will be balanced and the air flow will be matched to the WUFI model.
The ERV seems to be behaving as expected. The latent recovery varies but will be around 68% for our setup, according to the Venmar documentation. Altering interior moisture levels is slower than it would be with an HRV, but it is more effective at higher ventilation rates. At maximum, the recovery rate is only 48%.
When I purchased the unit I was concerned about the effect of higher interior humidity levels. However, there has been no condensation on the triple-glazed windows with the interior relative humidity hovering around 55%.
Options for the well tank
I toyed with several options for the well tank setup. Around here, people often install a 30-40 gallon tank with a pressure switch that cycles on and off at 40/60 psi. There are advantages and disadvantages for choosing a large tank. One advantage is always having a large water store on hand during times of the year when the water table drops or if the well is simply drilled in a low water table.
One disadvantage is, if left uninsulated, all of that cold water in the tank absorbs heat from the house; you dump it down the drain every time you draw from the tank.
Another disadvantage is size. In our mechanical room a large tank is not an option. Several of the tradespeople working on the house mentioned a VFD (variable frequency drive). This is a piece of electronics that turns a normal pump into a variable-speed pump. The tank is much smaller and the pump is on demand. The pump speed maintains constant pressure in order to meet that demand. This allows multiple fixtures to be on at the same time.
Another option is a CSV (cycle stop valve). The inherent simplicity of this system led me to my final choice: A Pside-Kick kit (see Image #4 below). The valve with this kit maintains a constant pressure to vary the flow rate. This is much better for the pump and just throttles the flow. The pump impeller still turns at the speed it was designed for but moves more or less water and draws more or less power. The benefits over a VFD are described here.
I installed the Pside Kick kit along with two sediment filters. As filters clog the resistance to flow increases. A parallel run would provide less resistance to flow than having two filters in series so I plumbed the filters in parallel with the same PEX runs so the static pressure along each of the filter runs would be the same. Ball valve shut-offs were plumbed on either side of the assembly so future servicing would be much easier.
The installation is compact and it all fits under the ERV. My electricians pointed out that we can also mount the well motor control and the well disconnect under the ERV in order to keep all the well-related gear in the same place.
That is the current state of the mechanical room for now. I am expecting there to be much more progress in the weeks to come!
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