Now is an appropriate time to write about the heating and cooling of our “passivhaus-inspired” home. We are a few weeks into autumn and the night-time temperature has dropped dramatically in Maria Pinto, to between 4 and 6 degrees, although the day-time high is still in the low to mid twenties.
Yet despite the drop in temperature, we are still walking around the house in t-shirts without even a light jersey. I hadn´t really thought that this is not “normal” until I had various videoconference meetings today with colleagues in different parts of Santiago and everyone was bundled up in jerseys and everyone commented on the fact that I was in a sleeveless summery top in my home office. The maximum temperature in Santiago today was 26 degrees and here in Maria Pinto it was 25, so we were experiencing the exact same weather, but the way our homes were behaving was clearly very different.
Even though, thanks to the airtightness and insulation of the house, we currently have a very comfortable and almost constant ambient temperature (it has yet to drop below 20 degrees in the coldest moment before dawn), in the middle of winter we will still need to switch on the heat.
Choosing a heating/cooling system is a BIG decision for anyone building a house and all the options need to be taken into consideration from the design stage, if you don’t want to be buying gas, electric or paraffin heaters for every room in the house come winter.
But before going into the details of the heating and cooling system that we chose; it is important to remember a few of the main requirements of the Passivhaus standard which influence the decision-making process:
- one of the key criteria of the passivhaus standard is to consume a maximum of 15kW/m2/year in energy to heat the house. This number is calculated by the Passivhaus modelling software based on numerous variables that you put into the calculation.
- passivhaus aims to achieve a constant level of thermal comfort in the ENTIRE house (20 degrees in winter and 25 degrees in summer). As a comparison, in a “normal” house in winter you will probably have certain rooms heated in the evenings and early mornings, but other spaces such as bathrooms, are often freezing cold. And when no one is home, and the heating is switched off, the entire house is rather cold.
Now let’s get down to the details…
We choose an underfloor heating system that has the added advantage of also being able to cool the house. This is important because in a central Chilean climate, with very hot summers there is a real risk of over-heating in a passivhaus, as well as in “standard” houses. We chose this option for a number of reasons:
- It is the best option to provide a homogenous heat throughout the entire house, without having an aesthetic impact. It is an “invisible” system compared to radiators for example which are also effective heating systems, but which take up wall space and may impact the interior design of the house. For example, in our case it would have impacted the layout in the dining room and lounge where we have some key (and much loved) pieces of furniture. This may seem trivial to some, but the visual impact should be taken into account.
- Additionally, underfloor heating uses water at a lower temperature than radiators which impacts the energy consumption of the system.
Choosing the system and installing the required plumbing turned out to be the easy part of this process. We then had to consider how we would “power” the heating system. We mentioned in an early post, that so often people who have underfloor heating systems, switch it on the first winter and when they get their first electricity or gas bill, they quickly switch the system off because it is so expensive. The reality is that it is not the system that is expensive to operate, it is the poorly insulated house that requires the system to overwork to maintain a certain temperature.
An underfloor heating system can be powered by an electrical heat pump or by a gas boiler (or pellets, paraffin etc). We decided to use a DC Inverter Heat Pump because this is by far the most efficient form of generating heat. I don’t want to get too technical (because it took me ages to understand and Rodrigo was very patient in repeating the concept to me many times), but it is important to consider the concept “COP” which stands for Coefficient of Performance, and this basically means the ratio of useful heating or cooling provided by a heat pump, refrigerator or air conditioning system to the energy required. A higher COP means lower operating costs and higher efficiency. Instead of just converting electrical energy to heat (which if 100% efficient, would be a COP of 1), a heat pump uses the ambient temperature to reach a higher COP. Our heat pump has a COP of 4, which means for every kW of electricity used the pump produces 4 kW of heat (this is an efficiency of 400%). In comparison, a gas boiler has a COP of 0,85, which means that for every BTU of gas consumed, 0,85 kW of heat is produced (meaning an efficiency of 85%).
So hopefully it is clear now why a heat pump is a better investment from a technical perspective, even though a gas boiler is far cheaper in initial purchasing costs and some people also take into account that gas may be cheaper than electricity. But you would need a lot more gas to reach the same temperature, which ultimately cancels out the lower cost.
But our story doesn’t end there and this is where it got really frustrating last year…heat pumps come in different heating capacity, and the typical capacity available on the Chilean market is between 8 and 12 kW. Based on the modeling of our house, we only needed a heat pump with a capacity of 2kW. As a reference the smallest model available internationally is 3kW. Rodrigo spent months contacting companies and suppliers to compare models, but unfortunately the main players in the market were unable to provide a solution:
- LG: last year they discontinued their 3kW model and although their service was excellent and they tried to help us as much as possible with other models, the price was out of our budget (1/3 more than the budget)
- Panasonic: they have a 3kW model but this is only available in Europe, no exceptions
- Daikin: the office in Chile never responded to emails
- Midea: told us they could import a 4kW model especially for us as it is not a normal product in Chile, but the price was completely ridiculous
Our aim in giving these details is not to bash the companies mentioned, but rather to show the challenges that we faced in trying to obtain the right product for our house in a market that is not designed for this standard (yet).
In the end, we had to choose a Chinese model, which at least has been available in Chile for many years and is trustworthy with a good local distributor, Mekthor. However, this model has various programming restrictions that are not ideal, but we hope to see a good performance over the next few months. We will keep you posted.
As we mentioned before, this system will allow us to cool the house in summer, using the same principal. It will be interesting next summer to walk around barefoot on chilled floors. But for now, our focus will be on having warm feet and a very comfortable and cosy house throughout winter, without breaking the bank!