Energy Revolution in a Brooklyn Townhome
Monthly Archives: December 2009
We have been going back and forth for a couple months now, debating which backup gas heating system we should use for the solar hot water. What is set is using the Heliodyne flat plate collectors with the Heliopak heat exchanger. The collectors will be (3) 4’x6′ units that we have to line up on the roof laying at a roughly 20 degree angle but unconventionally with the long side against the roof. We have Landmark visual clearance issues from the street behind the building. The tank size we have assumed is 120 gallons and the system is roughly sized for 75-80% of the hot water annual demand for the 2 families. Therefore, it will cover close to 100% of the summer demand and probably 60% of the winter demand. For this reason, a backup heat source is necessary. We have been looking at the Phoenix Solar tank with a gas burner attached. It is a condensing direct vent burner which means that we can side vent rather than go up the chimney to the roof. This is good because we do not have confidence in the fire-proofing of the old brick and mortar chimney after seeing some of the areas exposed on upper floors.
However, the cost of the Phoenix is quite steep at around $6,500 after tax and shipping, so we checked into many other tank-less and condensing burners to supplement a water storage tank. While these will be cheaper in materials, the plumbing costs will increase and we will have more external parts to maintain. Something that I learned while researching the Navien and Bosch condensing tank-less burners (I think it applies to all of the tankless) is that they start their operation based on flow rate and not temperature. Why does this matter? If you are not using a solar thermal system to pre-heat your water, it doesn’t, because you always have 55-60% water coming from the city supply and for one faucet of hot water demand will need at least the lowest level of modulation on the burner for heat. If you have the water preheated to 100 degrees or even 120 degrees at your set point and the flow rate turns on the tankless burner, then you will get the base modulation for heat output (Navien is 15,000 BTU) that will bring your water higher than your set point. You will then have to have your mixing valve introduce more cold water to lower the temperature and you will have effectively reduced the efficiency of the system. We figured out a plumbing bypass to this problem which would be a separate temperature regulated zone valve, and while that would work it would add complexity to the system.
This week we are making the final decision, but it looks like we are going to push ahead with the Phoenix, do to the compact design and simplicity of operation. I will let you know if it changes and why.
Over the past several weeks, a lot of energy went towards getting the ductwork for our energy system ‘just right’ in efficiency. The passive house consultant and HVAC contractor had multiple conversation to specify even the smallest of details. For instance, one specification is to have the ducts lined with foam pads in lieu of the industry standard fiberglass. (FIBERGLASS? In the ducts that supply the air we breath? Not in this house!) With that detail and many others sorted out, the installation finally began today.
Also this week, the carpenters are installing framing for the windows. We’re days away from our window order and have our specifications ready. Since window openings are big holes in our air barrier, the framing and connections between the windows are super important. Any square inch left uncovered will compromise our barrier – allowing “ungoverned’ air flow into and out of the house.
We also anticipate a plumbing inspection this week and expect the solar hot water equipment to be ordered. Our cellar slab pour has been delayed awaiting an inspection because the sewer and storm lines will run below the slab. We initially dug down 12″ inches so that a proper drainage detail can be incorporated into the new slab and a layer of foam can be sprayed below it. As part of our sustainable practices we specify that 20% of Fly ash be incorporated into the concrete mix. Fly ash is a byproduct from the coal industry that has been proven to strengthen concrete when added. It’s essentially coal ash that would otherwise be dumped in landfills.
Stay tuned as we begin to close up walls and conduct blower door tests.
Stained glass windows:
We have 3 stained glass windows for this house that are in need of restoration. They have been sent to a local stained glass shop called Stain Glass Store on 5th Ave. in Park Slope. The windows are in such bad shape – broken pieces, bent all out of shape, etc., that it will take four weeks to fix. To wait the four weeks will delay our window manufacturing too much, so we are having a template made of the glass without the frame and sending that to Germany this week. Once the stained glass is fixed, it will be crated and shipped directly to Germany to be fitted onto the Optiwin windows. The stained glass will be siliconed onto the front frame of the windows, sealing them in place and allowing their full beauty to be visible from the outside (and meeting landmark requirements).
We have two skylights that we are replacing on the top floor. We did a search all around the country for skylights that would meet Passive House standards and could not find any that would be close. All of the window companies like Serious Windows, Thermotech, and even the German companies shipping windows to the US don’t make skylights, so we were out of luck there. We then contacted Wasco Skylights out of Maine since they are one of the larger North American skylight producers. I was connected to Alan Kinne from their Engineering division and I explained the tough requirements that we had to comply with. He said that they had recently tested and gotten approval for U-0.29 skylights for Energy Star, but didn’t have anything close to the U-0.14 that we are looking for. This was disappointing.
However, what was exciting and refreshing about talking to Alan was his immediate willingness to try to come up with a product that could satisfy our needs. He called me back the next day and said that he had located a triple-paned tempered glass from a Canadian company that would meet our U-value requirements and for the frame he thought that they could get a better U-value than they normally did by injecting their standard pvc frame with their nanogel technology. They are going to make and test the skylights in January and then we will see how close to Passive House standards they were able to get. Even if their skylight could not make Passive House Certification levels, based on a U-value in the 0.20’s we should be fine for our building certification because we have low enough loads in the rest of the building.