Modified hot water return systems in a green brownstone make a lot of sense. You want to minimize the amount of wasted water that normally goes down the drain while you are waiting for the water to heat up, thus the use of a hot water return, but you modify it from the normal hot water return system so that it also minimizes the amount of wasted energy.
Typically a hot water return system wastes lots of energy and the water savings is only secondary to its purpose. It is normally used not to save water but to provide instant hot water to the faucet – it is a typical convenience at the sake of the planet setup.
The most wasteful way, and actually pretty common way in “high end” homes is to have a return pipe situated on the hot water line near the faucet farthest from the boiler, creating one big circle to and from the boiler. Then you have a pump on that line.
The pump pumps the water in a constant circle so that the pipe is always full of hot water. The result is that you turn the tap on and immediately get hot water. For most people that is all they care about.
But the waste is astronomical by green building standards. The pump uses energy similar to a light bulb being on non stop and the pipes are constantly losing heat. Translated into money it might not be that much to the normal home owner – maybe a couple hundred dollars a year – because they are spending so much money already on home energy. What’s another drop in the ocean.
But to a green builder it is a huge waste.
In a green brownstone it is nice to have hot water to the tap quicker, but that is not the primary purpose of a recirculating pump in that house. The main purpose is that if you are on the top floor of a four story brownstone and the boiler is in the basement then you are going to wait many minutes before the shower gets hot.
And those many minutes translate into a LOT of water down the drain, which is not what green brownstones are about.
A hot water return, or recirculating pump system, eliminates that wait. But it also adds the issue of wasted energy.
That is where an energy efficient hot water return system differs. In the green recirculating system the pump only turns on the moment you want hot water. Hot water delivery is not as fast as if the pump was going the whole time because even though the pump speeds the water up you still have to wait for the cold water to clear. But remember the goal is primarily to save water and energy, not to have immediate hot water.
To further save water, you don’t turn on the tap to turn the pump on. You push a button near the sink which activates the pump. The pump turns on and pushes water through the loop, you wait a few seconds, THEN you turn the faucet or shower on. Instant hot water! At least from when you turned the faucet on
And not one drop of water is wasted.
Another option instead of a button is a motion sensor that turns the pump on. The logic is that you walk into the bathroom, the pump turns on and voila instant hot water when you want it. But studies have shown that 30% of the time it is a false alarm – you may just be getting tissue paper – so I don’t like a motion detector system because you are back to wasting energy.
Pushing the button is not complicated once you are used to it. One extra step.
Also, as soon as the water temperature gets lukewarm the pump is automatically turned off, thus saving electricity. This use of the pump only costs a dollar or two per year.
There are a couple pumps on the market that do this. One gimmicky one is called the Chilipepper pump. But I have heard it is crap. It sounds like a blender and has a reputation for breaking down.
Wirsbo offers the D’MAND® Hot Water Delivery System pump which is quite good.
But my favorite by far is the Metlund D’MAND pump. It is a tad more efficient than the Wisrbo and has a great reputation. It is super silent too.
That is the pump we have at the Brooklyn Green Show House. It sits in the basement near the boiler. There is a sensor at the top most bathroom that tells the pump to turn off when the temperature warms up. Each bathroom and the kitchen have a little button you push a couple seconds before you want hot water. Works like a charm.
The one issue is that we have to have the sensor on the top bathroom so that hot water is fully delivered all the way up there before the pump turns off. But this means if you push the button for the kitchen on the first floor, even though the water has arrived to where you want it in the kitchen the pump will keep running until the top floor pipe gets warm.
This is a small waste of electricity, although negligible. The main issue is that we are filling the stack to the top floor with hot water that will sit there and dissipate into the walls – wasted. Not a huge issue and definitely better than buying a pump for each floor (they run at about $350 each), but I’d like to tweak it a bit – maybe put the temp sensor in between the kitchen and the top floor.
This means you maybe get hot water a couple seconds later to the top floor but you don’t waste as much heat when calling water to the kitchen. I’m sure I could calculate it on the computer but it wold be too much effort for my attention span.