Heating System

I've thought about the heating system for the Mill Creek NetZero Home (MCNZH) for months now. The home will need a very tiny amount of heat because it's so superinsulated, super sealed, and passize solarized. The computer model that simulates the energy performance of the house (using HOT2000) has the MCNZH using 2500 kWh. That's roughly 6% of the heat that my renovated (with new insulation and windows) 1950s bungalow uses.

So we'll need the equivalent of 9 Gigajoules of natural gas per year for space heating. Given that being connected to the natural gas grid costs about $400/year, and 9 GJ are worth $50-$100/year, it makes no sense for us to connect to natural gas. Plus, Canadian natural gas production is waning, so I don't want to depend on having gas in the pipe in 20-50 years from now.

So we'll only be connected to the electricity grid. That leaves the following heating options:

1. A Seasonally-charged, Huge Solar Water Tank: This is what Peter Amerongen used for the Riverdal NetZero Project. I've eliminated this option. The system ends up being very complex, and I think that it loses too much heat from standby losses whilst waiting for the heating season to come around. Godo Stoyke told me that they modeled 1.5% heat loss per day, given a tank with R100 and heated to 90 degrees C. In the end, the benefit of whatever heat is left over from the summer in December, when you finally need it, doesn't justify the complexity.

2. Ground Source Heat Pump (GSHP):  I was pretty set on this option until recently.There's a new one out that can heat your hot water too (at lower efficiency because domestic hot water needs to get quite a bit hotter than space heating hot water). It is expensive, though. Like $25,000 for a tiny system. 

3. Baseboard Heaters On Each Floor And An Electric Instant Hot Water Heater. The big advantage is the heat delivery system is DEAD SIMPLE. The entire system is just so simple. Plus, although I'm not giving up on the concept of true net zero, we will have a wood stove in the home. If we burn fires during the winter (I know, I know, ground source pollutants - we'll consider the fact that we don't drive to be our offset for those), we will be using barely any electricity to heat with.

The question is, then, do we spend $20,000-30,000 on a GSHP that will almost never be used, or use the money to finance more solar electric, which will definitely be producing all summer long, regardless of how many fires we burn.

We've decided to go with the baseboard heaters.

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Conrad,

Thanks for another fascinating entry. I love this blog. Imagine if your annual space heating load is 100 GJ. This is probably a little less than the Edmonton average but a nice round number. That's 28000 kWh so if you heated your home with electric baseboard heaters that would cost you about $2800.00. A GSHP would save you 2/3 of that or about $1850. That might pay for the annual maintenance on your GSHP plus setting aside money every year to replace the compressor when it's totally obsolete in 25 years (the ground loops are maintenance free and should last for much longer than 25 years) plus the interest on the incremental capital cost of the GSHP over the baseboard heaters - say $10000 @ 7% or $700 dollars per year. 100 GJ of natural gas would cost you from $800 to $1200 plus the myriad of other fixed and variable charges. But in your example of 10 GJ per year, a GSHP would save you only about $185 per year over baseboard heaters. That's nowhere near enough to even cover the interest on your incremental capital cost. I think you've made a wise choice.

Thanks. In a way it's an example of Amory Lovins' "tunneling through the cost barrier". We are making the house so efficient that investments in efficient heating simply aren't needed.

And good point about the ground loops - in many ways they are an excellent investment for the super long term. In 200 years, I'm positive that they could be dug up and be in perfect condition.

Hello Conrad,

I know this may sound a little off base here but I think a masonery stove (possibly a light version) that uses wood as fuel. If there comes a time when we need to heat, cook, heat water, etc when we don't have gas then we can always heat our houses with wood. The problem with these stoves is that they are expensive and the house really needs to be built around them.

A good masonery stove would handle all the aspects that electricity can't.

I mentioned to another person about GSHPs that if you could make a local co-op with your neighbours then that spreads out the costs of installation, maintenance, etc. My problem with GSHPs is that the initial cost is so high and the electrical demand is quite high. If this cost could be spread out to more people then it becomes more ecological since the footprint is now shared.

Take care

Thanks Michael. It's not at all off base. I really wanted a masonry stove at the outset, but size/design considerations prevailed. My next MCNZH post will be about the wood stove that we will have in the home (78% efficient, surrounded by thermal mass). It's not as good as a masonry stove, but it will provide some of the resiliency (to other fuel shortages) that you alluded to.

How are you going to heat your water?

Without gas, is an on demand electric hot water going to meet your family's needs?

Or with electric is the best current option to just use a "regular" tank and insulate it well?

It's going to be a solar hot water tank (a relatively small system with only two collectors), that is boosted by an electric on-demand heater if it's not hot enough. So we'll be mostly using the on-demand heater (rather than solar) throughout the winter.

I have been wondering lately about using an on demand electric hot water heat to heat my home. The logistics of that are easy; but what I am looking for is information about using solar power to power the on demand heater, thus in effect getting "free heat". How expensive of a solar array would I have to emplace to run just my on demand electric h2o heater? My home is under 900ft2 of living space, well insulated, and currently is heated by an oil baseboard h2o heater. I want to eleminated the oil burner in order to free up my only chimeny (single flue) for my wood burner. Any ideas out there? olsenjamie@hotmail.com

I have been fascinated by the Riverdale project as well as this one. I have a couple of questions.
For the Mill Creek house you dismiss the Solar Water Tank used in the Riverdale project but seriously considered the GSHP. Even with the heat loss experienced by the tank, wouldn't the water temperature still be greater than the water temperature coming from the ground? If you did not draw DHW from the Solar Water Tank, and thereby not have to replenish it with cold water, would the hear loss be lessened a great deal?
I was suprised that you never mentioned radiant floor heat for either of the projects. Was this not an efficint manner of distibuting the heat, expecially since you do not need air conditioning?

What I like about the GSHP is that you install it, then forget about it. Once the boreholes are dug, the only active part of the system is the heat pump itself.

With a big hot water tank like the Riverdale one, you need multiple systems. You need a regular heat transfer coil to pull heat out when the water is more than 30 or so degrees (ballpark) because heat pump can't operate at very high temperatures. Then, you need the heat pump itself to pull the heat out of the water as it is going from 30 degrees to around 5 degrees. You don't want to keep operating the heat pump after that, because it might freeze the water. You also need a backup system - what if there isn't enough heat in the water to last through the winter? Finally, you have the complexity and risk that's involved with storing thousands of litres of water in a huge tank.

As for radiant in-floor, there is some robbing Peter to pay Paul with them, because we actually want our floors to be as cold as possible when the sun starts hitting them on a sunny day. Heating them up to 25 degrees with radiant heating before the sun starts warming them up would significantly reduce their capacity to absorb solar energy.

We ended up going with the absolute simplest, cheapest system available - the heat radiates, but it is transported through copper wires that will never break, and will never need maintenance unless someone kicks over a baseboard heater.

Mississippi John
Mississippi Mills, Ontario

Figuring out my heating needs is the biggest head-ache I have right now. I understand all of the pros and cons of different systems, and the costs involved with each, but truth be told, the logic does not over-ride my distaste for electric bb heaters even though I know they are a viable and cost effective option!

Regarding infloor radiant, I understand the view re: wanting the floors cold for when the sun shines on them. One thing that I am wondering about, however, is if you could use the radiant loop to circulate or transfer the sun's heat heat to rooms where the sun was not shining? This is my scenario: Lets say your floor temp is 21C when the sun starts to shine on a January morning at 8 AM. Then it heats up to 27C by 11 AM. If you could set the radiant floor to a circulation mode you would thereby move the heat to areas in your house that are not receiving direct sunn. Has anyone given thought to this? Perhaps it would be too complex with the various heat zones, but I'm sure it could be done with the correct controls?

M. John,

Peter Amerongen is currently building a home, the Parkland NetZero Home I believe it's been dubbed, that will do exactly that: transfer heat between concrete slabs.

I think that maybe our concern about the floors being too hot when the sun shines on them were a bit overblown. After all, they floors are rarely warmer than 18 degrees in December and January, when we need the heat most.

I understand your hesitancy about baseboard heaters. I hate heating our house with coal-fired power, even if I am going to offset the electricity at a later time. That's why we'll be doing 80%+ of our heating with wood.

Conrad

John,

The first question to ask when transferring heat is, "What's my delta T?". Let's say you pump water through the warm part of your slab which might be at 20C. If you're very lucky, you'll actually heat the water up to 20C. Now you pump that water into an area where the slab is at 15C. How much heat will you transfer with a delta T of only 5C? And as soon as you do start transferring heat, that delta T gets smaller (the warm area cools and the cool area warms) and your heat transfer becomes even less efficient. I'm not an engineer so I've never done any actual calculations, but my gut feeling is that you have to pump a heck of a lot of water to move a significant amount of heat. A heat pump would make the process more efficient but at what cost?

I've got thermocouples in the floor of Belgravia NetZero so we'll be able to see how fast the floor warms when exposed to sunlight, but offhand I would say that if your floor is warming 6C in 3 hours then you don't have enough mass.

B.

Re: "I understand your hesitancy about baseboard heaters. I hate heating our house with coal-fired power, even if I am going to offset the electricity at a later time. That's why we'll be doing 80%+ of our heating with wood. [Conrad]"

I don't get it...you said you're not going to be connected to the grid, but you will still be using coal-fired power? Where does it come from then, if not the grid? Forgive me, I am new to all of this and don't understand many of the concepts yet.

We are connected to the electricity grid. We are not connected to the natural gas grid.

Conrad

Got it. Are there ways to be off-grid with electricity as well?

There are, but it involves batteries, which are hugely expensive, wear out after a while (and therefore need replacing), and require a backup generator (diesel, gasoline or propane) for when the sun doesn't shine for a long time.

Quick questions for Conrad and Bob,

I am surprised that your floors are rarely more than 18C in December and January. Is this possibly due to a basement that is unheated at this stage in the home's use, and do you expect this to change if you ever rent the basement space? Would a 4" thick floor behave more advantageously?

I intend to place 6" of foam underneath my 4" slab, which is also the main floor of the house. I would not want to go to the expense of building my R50 walls, with my fibreglass windows only to have cold floors. Does the floor seem cold at 18C? or is it merely a case of needing slippers or warm socks?

Lastly, Bob, is the performance of your floor similar? Thanks again - this forum is so valuable!!

Mississippi John
Mississippi Mills, Ontario

Our basement is rented. I think that making the floor thicker would make it even colder.

The floor doesn't seem cold at 18C (we do wear slippers though). In fact, the house feels warmer at, say, 17 degrees, than a conventional house does, because the surfaces of the outside walls are so warm. They radiate more heat.

I'm sure that our floors would be warmer if we weren't so stingy with the heat :) Furthermore, our heating isn't in-floor.

Conrad

Thanks for the replies!

Mississippi John
Mississippi Mills, Ontario

We are about to embark on the adventure of building a new super-insulated home, although we cannot afford to go the net-zero route at this time. We have reluctantly come to the same conclusions that you did regarding heating our house - I say reluctantly because infloor heat was something we both dreamed of! Given that energy efficiency is key, what kind of electric baseboard heaters are you using? Are they necessary in every room? And what do you think of the idea of using electric heating mats under the concrete in select places that do not get any south exposure (ie. the main bathroom)?

Gerry,

Electric resistance baseboard heaters are all ~100% efficient. Any wasted energy is lost as, well, "waste" heat. Since their job is to heat, there is no waste.

We figured out the design heat loss for the house. It it is about 8400 Watts at our design outdoor temperature (it may be different in your region). We then shot a bit higher than that and installed 10,000 Watts of baseboard heaters. The whole system still only cost us $900 installed.

The heating mats idea sounds pretty cool.

One other piece of advice: if you are the type of people (like us) who will only turn on the heat in the rooms that you are occupying, oversize the baseboard heaters in the room(s) that you use the most.

For example, we spend 90% of our time in our kitchen/dining room/living room space. In -25 weather, only the 2000 Watts heaters that are in that space are turned on. It's not quite enough, because they are the only heaters in the house that are turned on.

If we were to do it again, we would install 3000 Watts in that space. Then, in really cold weather, the heaters would be better at keeping the space warm.

Of course, all of this is rendered moot by the point that 90%+ of our heating will actually come from wood. :)

Conrad

Conrad,

What suggestions or observations do you have about the placement of the heaters so the heat would be distributed evenly?

Did you install a heater(s) in every room? Thanks.

Jim

Jim,

In a super-insulated house the heat can't escape through the walls, so it tends to spread itself out evenly.

That said, we have a heater in every room except the bathrooms and the utility room downstairs.

We only run a few heaters at a time though, and the heat distribution is very uniform.

Conrad

I read a presentation by Marc Rosenbaum recently where he had spec'd the energy needs of a house with a single point source minisplit air-to-air heatpump for both heat/cool, along with a boost fan (fantech) for simple air circulation throughout the house. I would see this as the simplest way to go, get a nice low powered fan that would pull from low and dump from the same registers the HRV would use, or to another run.

You're already going to be pretty uniform based on the insulation levels, but a little fan would probably go a long ways in a house like that.

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