Energy harvesting from hot pipes in home

[GBA13]

Hi guys,

I was just thinking about something and I'd love to get your opinion. How much energy do you think is lost from water pipes getting hot and releasing that energy into the air? In a three bedroom house there are probably a lot of hot pipes releasing heat energy. Do you think some sort of cladding could be put around them to harvest the energy and do you think there would be a decent power output?

Thanks!

 

[Randy Beikmann]

It would be much more effective to insulate the pipes. Instead of "harvesting" the energy with a complex device, you could prevent the thermal energy from escaping the pipes in the first place. Simple and cheap.

 

[russ_watters]

Agreed. Most houses don't use much energy for water heating anyway and the fraction of that that is loss is small.

 

[billy_joule]

Agreed. Most houses don't use much energy for water heating anyway and the fraction of that that is loss is small.

Well that depends on climate. HW is metered separately in many houses in New Zealand, few houses have AC or central heating, I've had bills where half the kWh is HW, 35% was about the average.

 

[russ_watters]

Well that depends on climate. HW is metered separately in many houses in New Zealand, few houses have AC or central heating, I've had bills where half the kWh is HW, 35% was about the average.

Ok, so if the energy usage of a house is really, really low the fraction used for water heating can be high. But that doesn't really change our issue does it? The amount of energy spent on water heating is still low and the energy available to be recovered is still tiny.

To put some numbers to it though, my home is heated by propane, which is probably half the cost of electric for heating, but in any case, that means I get a separate bill for it. In the summer the combined total propane usage between hot water, cooking and clothes drying is $15 a month. A good guestimate is that the water heating is half of that. In the months when I don't need heat or air conditioning, my electric bill is about $40 a month. Converting the propane cost to an equivalent electric cost, that equates to about 20% spent on the water heating. Now, I'm single and male, but still I find it hard to imagine how a house's energy usage can be such a high fraction for hot water.

But still, the bottom line is that the energy cost is only $15 a month if its electricity, which doesn't leave a lot of potential for saving money by recovering some of that energy.

 

[Bystander]

more effective to insulate the pipes.

... plus, an "S-bend" to "trap" convection losses on vertical plumbing runs, and you've taken care of just about everything.

 

[jack action]

With cold climate, there is nothing to gain as you need to heat the house anyway. Heating water that warms the surrounding air or heating the air directly, same difference.

 

[cosmik debris]

Ok, so if the energy usage of a house is really, really low the fraction used for water heating can be high. But that doesn't really change our issue does it? The amount of energy spent on water heating is still low and the energy available to be recovered is still tiny.

To put some numbers to it though, my home is heated by propane, which is probably half the cost of electric for heating, but in any case, that means I get a separate bill for it. In the summer the combined total propane usage between hot water, cooking and clothes drying is $15 a month. A good guestimate is that the water heating is half of that. In the months when I don't need heat or air conditioning, my electric bill is about $40 a month. Converting the propane cost to an equivalent electric cost, that equates to about 20% spent on the water heating. Now, I'm single and male, but still I find it hard to imagine how a house's energy usage can be such a high fraction for hot water.

But still, the bottom line is that the energy cost is only $15 a month if its electricity, which doesn't leave a lot of potential for saving money by recovering some of that energy.

This kind of cost stuff is really very relative to where you live. I agree with Billy, I live in New Zealand too and our water heating costs are a significant portion of our electricity bill. Also unlike the US for example, we don't use diesel for central heating because it is really expensive here, so is propane. Electricity is our cheapest form of energy, apart from domestic solar. Even domestic solar has hidden costs that many people fail to take into account. Pipe lagging is a really good thing to do here.