This is a story of how to retrofit heating in a Victorian weatherboard house as part of an all-electric home.
Heating and cooling accounts for around 40% of energy consumption at home. It is a big deal and has a significant impact on our comfort at home. And in Melbourne, heating is a bigger factor than cooling, with up to 5 times as much energy used to keep a home warm in winter, as is used to keep a home cool in summer.
This blog documents how we transitioned from a gas ducted heating system to a hydronic heat pump system at our place, to maximise use of our solar and battery system and help us move towards a zero emissions house.
Why change and why hydronic?
There are a lot of different types of heating and cooling systems on the market. The operation and capital cost of these systems isn’t cheap. You’ll spend far more on your heating and cooling (the appliances and in running them), than you will on your fridge, oven or tv.
We had a gas ducted heating system and decided to change the gas ducted system due to the following issues:
The ducts were decaying (you only know that after crawling around under the house) which means you are essentially heating the air under the floorboards
It uses gas – a fossil fuel – which we know we need to stop burning for climate reasons
It blows small particulates through the vents – so not a great indoor air quality outcome
The fan uses quite a bit of electricity (so gas and electricity use both peaked in winter)
It is hard to zone or scale. While you can close vents in some rooms, that actually increases the pressure on the underfloor duct system, as the pressure remains the same but there are less locations for the hot air to flow into the house
By not using any gas at all (meaning we are not using gas for hot water heating or kitchen cook tops) we could save $400 a year just through not paying for the connection fee.
Some say gas is cheap to run. I disagree. I distinctly remember getting a $600 winter gas bill for just a two month period when gas was cheap (which doesn’t factor in the increased electricity bill that month too).
We chose hydronic to replace the heating system on the basis that it provides a nice comfortable (silent) heat, and with a heat pump system can be achieved very (energy) efficiently, and doesn’t require lots of heads to be located high in each room. I am not against reverse cycle air con (we actually have one in our lounge room to use on most days instead of the evaporative system), but this is a more comfortable heating system.
We chose a wall mounted hydronic system, meaning the heat travels through a dedicated (and closed loop) pipe network under the floor, to each panel in each room, with cooler return flow water flowing back to the buffer tank. This is a different solution to a hydronic in-slab system, which wasn’t possible unless you can rip the flooring up and lay a new concrete slab with hydronic coils running through it!
The system design
We considered several systems and chose a Stiebel air to water heat pump system, purchased through Hydrosol. We needed 10 outlets: 8 rooms with wall mounted panels and 2 towel rails in bathrooms. We estimated the heat load based on a thermally efficient house. We found that most suppliers tend to overestimate the load, and are more interested in the load of the panel- not the appropriate temperature of the room or how to reduce the overall energy demand to achieve a comfortable house.
We selected a Stiebel Eltron WPL 17 ACS classic, with an output of 8.5 kW, and a Coefficient of Performance of 4.86 (which is the eratio of energy inputed to energy generated – more than 1 is good!). The system includes:
· 1 x Air to Water heat pump WPL 17 ACS Classic
· 1 x Hydraulic module HM Trend
· 1 x FEK Relative humidity remote control unit
· 1 x Safety temperature controller STB-FB
· 1 x Buffer cylinder SBP 100 E
· 1 x Internet-Service Gateway ISG web
As this is a heat pump, it can heat and cool in reverse cycle. More on cooling below.