Heating and Cooling Systems Replacement

Table of Contents

Existing systems

• One open fireplace in living room (original classroom)

• One slow combustion wood fire in family room (1988 extension)

• One ducted oil heating system throughout old school section

• One reverse cycle A/C unit in attic bedroom (1988 extension)

• Electric off-peak domestic hot water system (external tank)

• One EverHot wood fire stove and oven in kitchen (in addition to a gas upright stove and oven) with disconnected gravity hot water tank above kitchen still in place.

• Two reverse cycle A/C systems in annex upper level

• One slow combustion wood fire in annex lower level (entertaining or rumpus room and or workshop)

• Physical activity

• Lap dogs

This is a pretty eclectic but typical collection of systems in a building with this history - almost a museum of heating technologies. With the exception of the lap dogs and physical activity it may be time for a complete update.

Reuse of the old fireplaces

The working open fireplace, which is also home to the occasional bat family, will probably be converted to a high efficiency wood or gas fireplace to retain some traditional ambience for use on special occasions.

The four now-disused open fireplaces with capped chimneys will become havens for living plants and other decor that contrasts with the original purpose. What was the original 1880 kitchen fireplace, and now a large and hefty stone and brick wall cavity, would convert quite nicely to a wine "cellar". The room's modern function could be described as a small reception room and is the coolest part of the house.

Local Inspiration

If I walk 200 metres up the road to where the sign says "Great Dividing Range - Altitude 964m" I can see the blades of the Crookwell wind farm large and lilting just 5km away. This was Australia's first grid-connected wind farm and the view below is from the observation platform looking back toward Crookwell. I'm told these turbines are just 40 metres tall.

A second new wind farm has been built next to the old which started operating in 2019. These are 120 metre turbines and join a line of wind farms stretching along the range all the way to the distant horizon near Gunning in the south. I understand that power from this farm supplies Canberra, which intends to be using 100% renewable energy by 2022. A third wind farm is planned on land adjoining the Crookwell two farm.

Personally I find them to be things of beauty, perhaps because they represent a tangible and harmonious connection between the planet, our shared environment, and the essentials of modern life. Far better than smoke stacks on the horizon.

Having been driven on many occasions as a child through the equally beautiful countryside of Victoria's Central Gippsland it was always tainted by the horizon-to-horizon haze and the ever-present sulfurous odour eminating from it's brown coal power stations, the contrast is stark.

When it comes to generating power from the solar system's biggest and only fusion reactor, the Sun, it is always shining and the wind (driven by solar energy from the Sun) is always blowing somewhere on the planet, and especially on a continent the size of Australia the engineering problem to solve is really energy distribution.

Mythbusting

There are many adverse claims made about industrial sized wind turbines, some no doubt have some kernel of truth to them but some are outright mis[chievious] information. One complete falsehood is that the energy required to manufacture and install a turbine is equal to or greater than the energy they produce. This analysis indicates that the EROI (Energy Return On Investment) over the life of a turbine is 20 to 25 times. Another [manufacturer] source claims that EROI is achieved within 3 to 6 months of operation. Using the back-of-the-envelope method, globally in 2012 there were 225,000 wind turbines and at the start of 2017 there were over 341,000. So, how much of the total energy generated from wind would have been needed to make the additional turbines installed between 2012 and 2017? Answer: assuming all turbines are identical and an EROI of six months (i.e. the energy produced by one turbine over six months is enough to make one new turbine), it's a "compounding interest" problem, i.e. with a starting number of 225,000 and a target number of 341,000 after ten six-monthly periods requires a rate of 4.25%.

In with the new - geoexchange

Looking at current trends in power costs I've thought about solar PV, solar hot water and wind. But geoexchange has grabbed my attention because it's a technology that improves efficiency of existing electricity supply rather than directly replacing sources - it is a source of energy but it requires another source to extract it. I'm going to need to stay connected to the grid for a while, and although I've heard that economical storage technology for completely self-contained energy supply could be just a decade away, whatever the source it makes sense to make any use of energy as efficient as possible. Geoexchange appears to do that and won't be made redundant if I add another source, such as solar PV, later on.

Geo Exchange Interface

Trenches are not an option due to the location of the building envelope relative to available open space, and regardless, I didn't want the subsequent restoration work for grassed areas etc. because another of my projects is turning what were paddocks into a park-like environment.

The bore holes for the vertical ground loop would be drilled in the backyard.

The presence of permanent ground water (evidenced by monitoring the well in the back yard throughout the year) in theory improves the exchange of heat to/from the ground and so that is also positive. An open loop system is not feasible due to insufficient inflow to the well, which is only about 0.5 to 1 litre per minute by my calculation.

Domestic Hot Water Tank

The external domestic hot water tank would be replaced by an internal tank, protecting and insulating the tank further from the elements, and cleaning up the rear of the house still further. This tank would be heated by the geo system heat exchanger throughout the year, and in summer will effectively store the heat that is a by-product of the A/C cooling cycle, that is the so called "hot water for free" that is often promoted with geo exchange systems. This last aspect depends on thermosyphoning, so the piping between the DHW tank and the exchanger has to be carefully designed.

Hydronic Buffer Tank

A hydronic buffer tank would be installed and connected to the heat exchange unit. This tank provides either hot or chilled water for air conditioning throughout the main residence and possibly the annex upper level also.

Fan Coil Units

I'd prefer ducting and a single FCU rather than wall-mounted FCUs in each room because of the need to run condensation outlets from each FCU. In the old school section the walls are about 450mm thick and I don't want to have pipework possibly defacing the exterior stonework.

Zones

Three zones would work well:

1. Old school building - mostly heating in winter

   1. With it's mass in the walls the temperature inside the old school building tracks the average day/night outside temperature over several days. This summer (2014/2015) was mild with maximums around 30°C and minimums around 12°C. Measured temperatures inside were almost a constant 21°C on those days (and nights). The old classroom with it's large north/west facing windows was generally about 3°C warmer than that during the afternoon, which is not uncomfortable for summer. Humidity is noticeable only a few days each year. Running the FCU in fan-only mode would even temperatures throughout.

   2. I want to supplement heating in winter by putting a high efficiency wood fire into the open fireplace in the old classroom (now the lounge). This would be used on special occasions for ambience and on particularly cold days or nights. If the return air vent for the ducted system is also in this room, as it is now with the oil heating, then warm air from the fire will be circulated throughout the building, taking some of the load off the geo exchange system.

2. Extension - heating downstairs and cooling upstairs

   1. Occupied all year round and a fairly typical seasonal heating/cooling requirement. Currently has a slow combustion wood fire downstairs and a reverse-cycle A/C unit upstairs. Between the two I've been able to manage heating and cooling throughout the extension fairly well throughout the year.

   2. The new HVAC FCU will mainly service the three upstairs rooms with ducts in each room while a fourth vent will supply the kitchen downstairs. The stairwell will also act as a passive connection between upstairs and down. Cool air will fall, and warm air will rise. The location of the return in the stairwell will pull in warmer air from downstairs and distribute it, warming it further or cooling it as appropriate.

3. Annex loft - mostly cooling in summer

   1. The annex loft is generally warm on the mostly sunny winter days we get here and is a space primarily used for daytime activities. Considering a simple evaporative system as an alternative for this zone.

So, the system's capacity could be mostly directed into zones 1 and 2 during winter, and zones 2 and 3 in summer.

Secondary Gains

• Removal of external eyesores:

  • oil heater chimney

  • oil tank

  • hot water tank

  • external A/C unit on roof

  • electrical conduits removed from roof.

• Removal of redundant slow combustion wood fire in family room plus flue through the roof. This opens up several options:

  • putting in a doorway to a new deck and garden at the rear of the house.

  • putting in a new dormer window to provide symmetry to the existing one and more light and ventilation upstairs.

Future additions

PV panels

With a heating COP of 4 or so for the geoexchange system, an average 5kW solar PV array could deliver up to 20kW of heating plus hot water, and all required cooling, for much of the day. That's also about the limit of the power that can be fed back into the grid.

Off-grid battery storage

This is the ultimate aim.

Progress

Oil heater removal

For some reason I'd assumed the heating oil tank was empty, but it turned out to be half full. Now what to do with the approximately 220 litres of oil. I decided to burn it by running the heater on full for as many days as it took, and it took about 10 days running 24 hours a day.

After that the tank was the first item to go, then on to remove the chimney and then to dismantle the corrugated iron enclosure to get to the furnace itself. Once exposed it was on to cutting the ducts and then removing all the parts I could to reduce the lift weight. Part of the enclosure houses the water pumps and I would be keeping that section of the enclosure for now. So I would need to maneuver the furnace unit over the top of the pump enclosure to get it out.

The whole system went to scrap metal for recycling. I should have kept the stainless steel flue to use in the new lounge wood fire insert.

The new geo heat exchanger unit will go in this alcove but is less than half the size of the furnace it replaces. The 400 litre buffer tank will also go here as we have determined it won't fit inside. There is no ducting directly connected to the new unit, so there was some repair to be done to the walls before it goes in.

The extremely rough holes have been bricked up and rendered. Fortunately circumstances have given me time to do a better job of this than I expected to do. As you can see above (images 9 to 12), as my first attempt at this kind of thing with help from Youtube I've managed to do a reasonably good job. The final render coat was 1:1:6 cement:lime:yellow sand as my attempt to match the colour. It won't match but will be a lot closer than the straight cement:sand mix used underneath it. This was nothing more than a guess assuming that the original would have been a similar mix with the main colour being in the sand, which I am guessing was the more common yellow sand (there is a tinge of red in the original) rather than a less common in these parts white or grey sand. I'm not sure when the original job was done but reasonably sure it's not part of the 1880 build.

Removal of the Old Disused Gravity Hot Water Tank

I found this tank behind a panel upstairs. It was replaced at some point by the current electric tank at the rear of the house. With a pair of good angled sheet metal snips and a pipe wrench the tank was disconnected and cut up in place and removed through the access panel. What was a major concern turned out to be a simple process, and some good advice found via Google convinced me not to use an abrasive cutting wheel that could start a fire. The tank still contained some water (about a quarter full). Removing the drain plug and tilting the whole tank emptied this sediment-laden water into the drip tray where it drained to the outside.

The copper sheet that made up the inner tank will get used in some other project.

Removal of the tank will make it easier to run ducting and electric cabling through the roof space, and allow some expansion of the floor space in the smaller of the three attic rooms.

Lounge Fireplace Insert

The open fireplace has been replaced with a wood fire insert as part of the old schoolhouse interior renovation.

Here the render has been removed from the wall (all walls) and still deciding how and if to rerender the whole wall or leave some stone exposed.

Rainwater Filters

I'm installing a whole-of-house filter system to protect the new HWS from silt and other contaminants. It consists of two inline filters, 20 micron and one 5 micron washable, each 120 ltrs per minute throughput, sited in the pump box between the pump and the house. Over time I will also improve the rainwater collection and storage system which is pretty basic at the moment.

Geo Exchange system

Installation is almost complete and is an 18kW DX system with vertical loop field. It will service just the main house initially (2 zones - see above). The annex zone will have to wait until I can join up the two buildings in some way to provide a protected route for the pipework.

I expected the trenching to possibly cut through some of the underground rainwater pipes and had asked the contractor to note their locations so that I could repair them. They obviously forgot that request and repaired the two breaks they did make themselves. But unfortunately they leaked, producing two mud pools whenever it rained, which also meant any rain had to fill the entire length of pipe before any, possibly contaminated, water got into the tank.

Before photo 19 was taken I had already dug out both sets of joins: the pile of clay in the forground and another next to riser at the tank; and found they had used PVC joiners. Three of the joints had no glue applied at all.

After one more failed attempt to fix them myself on the cheap and not wanting to risk missing other leaks I got the worker in the photo to dig out the longer section of pipe with his machine while I went into town to buy a new length. I'd already bought four neoprene joiners with stainless steel hose clamps. Once fixed we filled around the pipes with sand for support and then finally he continued the job he'd come for.

Removal of the Family Room Wood Heater

It's now time to cut ties with the old and commit to the new.

It's not yet Winter but I'm confident the new HVAC system will handle the load, although I'm sure some adjustments will be needed to both it and the building in order to get the most out of it.

It's a tidier presentation when viewed from the public lane [camera position], which is the only public view of the old schoolhouse. It also cleans up the vista looking out of the schoolhouse window that looks across the rear wall of the extension.

Update

Ground loop failure

In September 2020 the ground source heat pump suddenly stopped working. It was eventually determined that two of the DX ground loops had developed leaks that did not go away after a leak repair agent was injected and so, as all six loops are connected via manifolds, the entire loop was unrepairable.

The cause of the leaks, which appear to have developed independently within a year of each other, is assumed to be corrosion. The loop field was installed with a sacrificial zinc anode but these do not last very long in the wrong conditions.

After five years the system was also now out of warranty and the original local installer had sold his business. The cost of digging out and replacing the loops would be more than it cost to install them initially. The old system required about 9kg of R410a and had already been regased twice at approximately $900 each time over a two year period before the leak was confirmed in the loops.

Controller feature downgrade

Just after this and unrelated, the developer of the HeatView control system appears to have switched off their remote control feature. The system still works locally but I'm now looking to convert to a new controller and make some changes to the hydronics inside.

How I check performance over time

I use a simple repeatable test regime that gives me an unofficial COP value that can be used to check performance periodically, and in this case to compare the new heat pump to the old heat pump. It simply measures the actual energy used to heat the buffer tank and compares it to the (inaccurate but consistent) theoretical energy required. The inaccuracy comes from not knowing the precise volume of water in the buffer tank, which is nominally 400ltrs, but it is the same buffer tank each time hence it is at least consistent. I calculated the new system's heating COP at about 3, which was much the same as the old system. Ideally, run this procedure on similar days with respect to ambient temperature and humidity.

The regime is as follows:

1. Disable all hydronics for the duration of this procedure.

2. Switch the heat pump to cooling mode.

3. Bring the buffer tank down to a set temperature such that the temperature is read as the water in the tank has been mixing.

4. Switch off all other electrical devices and note the current power meter reading.

5. Switch the heat pump to heating mode.

6. Bring the buffer tank up to a set temperature.

7. Note the new power meter reading and subtract the initial reading to get actual kilowatt hours used.

8. Subtract the higher tank temperature from the lower temperature to get the temperature rise.

9. Multiply the tank volume (litres) times 4.186 times 0.00027777778 times the temperature rise to get total theoretical power in kilowatt hours.

10. Divide the theoretical kilowatt hours from (8) by your actual kilowatt hours used to get your COP.

Example:

Nominal tank volume: 400 litres (400 kg water)

Initial temperature: 11 deg C

Final temperature: 55 deg C

Starting meter reading: 14859.6 kWh

Ending meter reading: 14866.3 kWh

Theoretical power required: 400 x 4.186 x 0.0002778 x (55 - 11) = 20.465 kWh

Heating COP: 20.465/(14866.3-14859.6) = 3.054

The cooling COP is done similarly by bringing the tank to the higher buffer temperature in heat mode and using cooling mode to bring it  down to the lower temperature. The cost of running this regime to obtain both the heating and cooling COP is less than that of a cup of coffee.