Very high energy bill in 8 year old house – no apparent cause

[Sarah Grant]

Hello all,

I’ve just done to a tricky Home Assessment for a customer who has a reasonably new home (built 2006). He lives there with his 3 teenagers and his last power bill was $650 for 2200ish Kwh (actual read). It’s been almost bang on 30 days since the date of the last power read and according to the current meter reading, this month’s bill will be around $550 – $580 including fixed charges. The family have been living there for 9 months and have had bills that are approximately double what they had in their previous home which was a “draughty villa”.

They’re not warm in the current home and the sole form of heating is one small heatpump in the kitchen/dining area. They have an HRV system with two fans and 6 vents. There are no problems with condensation or other moisture or ventilation problems. The thermostat is set to 23degC, and the house was at 15degC when I was there. The roof is shingle tile. The only insulation they have is pink batts in the ceiling – not particularly well installed.

I couldn’t find an obvious reason for their high power bills, and suspect it’s a combination of factors that all collectively contribute to higher bills. He tells me their behaviour and the bulk of their appliances haven’t changed since their last house so I think it’s building related (ie greater hot water flow rate, lots of lights etc).

The house has over 40 downlights, almost all with 100W incandescent bulbs. 21 of these are in the living/kitchen/dining areas so with 8hrs of use a day I calculate they contribute to a significant proportion of the power bill ($4.11 per day for these rooms only).

They also have a spa which the owner was adamant only costs them $1 a day to operate (turned off overnight as it’s too noisy, on again every morning to reheat – same practice as their previous house, same spa). I’m not familiar at all with the power requirements of a spa but it appeared there were two components (I assume one was a pump and the other a heater) one rated at 1100W the other at 1500W.

Pipes aren’t lagged, showers are approx 13 minutes x 4 per day at a flow rate of approx 14L/min (which means 728L-ish of hot water on showers alone!). Temperature of the hot water at the tap is 44degC. I’ve suggested that hot water use is a major component of the houses energy use and to conserve it as much as possible but it would be best to be able to quantify exactly how much energy the hot water system is using – unfortunately they’re on a single meter so I can’t tell.

I think he wanted me to find a specific reason and was a bit disappointed when I discussed these possibilities with him as there’s no ‘magic bullet’ to reduce the power bill. I’ve recommended he contact Contact and ask if they can tell him if the power bills they’re experiencing are typical of the previous occupants, and if they can drill down into the power use information to provide time of use data for more clues.

I’d appreciate some guidance from you guys who’re more experienced than myself – if there’s anything you think I’ve missed or something that you regularly see I’d love to hear about it. What do you guys think?

Thanks in advance for sharing your experience with this noob!

🙂

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[Ian McChesney]

Hi Sarah
Good to get the time of use data to see what the patterns are, but it sounds like you have pretty well sorted what is going on here. These calculations are a bit speculative but: – the hot water use for showers alone suggests about 700kWh in the month. The lighting could be adding up to 500kWh – most of which will be heat going into the ceiling I suspect, as well as heavily compromising the insulation. Add to that HRV fans (could be 100+kWh depending on amount of use – and also check whether they have any in-line heating elements which could add another 1 or 2 kW ), the heat pump (4 hours per day at ~1.2kW (for a small HP) gives ~150kWh), maybe another 100kWh for the spa (and this might be low), computers/TVs/games consoles etc, esp if lots of use from teenagers, could be 100-200kWh, washing/dishes/other hot water etc (another 100-200kWh), plus cooking etc and we’re up at ~2,000kWh.

The lights look like one area where some decent improvements could be made, and a good, lower flow shower head might be effective at cutting the hot water use (I’d go for technical solutions over behavioural solutions where teenagers are concerned…).
regards
Ian

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[Ian McChesney]

I should have added – the possibility there is a problem with an appliance, or the hot water system. Thermostat issue on fridges or freezers? (I forgot to ask about multiple fridges etc). Also, while rare, hot water leaks in out-of-the-way places are not unknown.
Ian

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[phillcoxon]

Thought I’d chip in and say that we’re having similar issues in our current house with power bills looking to be in excess of $600.

We’ve partly tracked this down to a faulty thermostat on the hot water tank which had increased the tap water temperature to 80 degrees C! (We knew it was hot and were “getting around to” fixing it but hadn’t realised it was THAT hot). We’re now turning it down and retesting every couple of days to get it to a more reasonable level and see if it will hold.

It’s also an older hot water tank with an undersized heating element so we suspect it’s running for long period each day just to maintain water temperature. We had a plumber come in to install a higher wattage element on the basis that it will heat and maintain the water temperature much faster and hence use less power overall.

Unfortunately the existing element is completely stuck and unable to be extracted without risk of damaging the tank so we’re exploring other possible solutions.

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[Norman Smith]

Hi Sarah,

small world, only yesterday I had a look at a neighbours house built around 2007 which is both cold and expensive to run. No silver bullet but the no-brainer starting place for them is their 14 downlights in the kitche/lounge. These were installed at the time when a 300mm gap was required between ceiling insulation and the light fittings. This means huge gaps in insulation. Given the warm air will bridge through these holes the end result is, in effect, very litle insulation and so its very hard to get/keep the place warm. So as well as the running cost of the lights its also the heat loss.

My recommndation to my neighbours is replace all fittings and lamps with AS/NZS60598.2.2.(?) compliant ones so they can put insulation right over the top. They cost around $60-70. What they might do is take some of them out and use the money they save to contribute towards the cost of having the holes plastered and painted’ I mean who needs 14 downlights in a single room! The quality of the light, longetivty and running costs is greatly improved and LEDs offer a much broader and flexible spectrum of design options to choose from.

I’m sure you will understand the issues about doing this properly and not simply going with an LED bulb replacement whch means you cannot safely cover it with insulation.

Cheers, Norman

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[Ian McChesney]

Hi Sarah
Regarding technical info on ventilation systems, you are right, suppliers are very vague about this info. I did a report for EECA on home ventilation systems about 5 years ago, and the following is what I wrote about typical fan specs and running costs:

“Energy for fan operation – this depends on air flow rate, pressure and resistance in ducts, efficiency of fan and motor, fan speed and operating time. Most fans/motors used in PP-RCHT systems typically draw power in the range 20-100W with suppliers citing running costs typically stated as “8 cents per day” or “no more than an average light bulb to run” etc. These costs typically work out to be around $2.50-$10/month, which with electricity prices of about 20c/kWh equates to some 12-50kWh/month. In fact it is quite difficult to determine how much electricity PP-RCHT systems will use because of the many different assumptions used about fan flow rates, operating hours, pressure and resistance in ducts, pressure within the house, efficiency of fan and motor etc.

AirCare Ltd (suppliers of the Homevent system) is one of the few suppliers to provide a transparent calculation on their website. They cite a maximum fan load of 85 Watts, with a typical load factor of about two-thirds (i.e. 57W). Energy use is thus 1.36kWh/day, or ~41kWh/month ($8/month). This is at the higher end of costs cited by suppliers.”

Newer systems may have improved somewhat, but the above is probably still reasonably applicable for older systems.

The specs for heating units (if installed) – generally they come in size increments of ~1kW.

Regarding the warming of the roof space with the downlight heat – not sure that there would be sufficient heat to raise the cavity temperature that much? I imagine the roof cavity is fairly large, with a large area of exposed roof that will lose heat quite rapidly most evenings. I guess the householder could monitor roof cavity and house temperature differentials by checking the HRV controller regularly for a period?

Hope this helps
Ian

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[Sarah Grant]

Hi Ian and Norman,

Thanks very much for your input. I went over the lighting in detail (chimney effect, cost to run, inefficiency of the incandescent bulbs etc) with the customer and also recommended upgrading the fittings to IC-F rated ones and installing insulation over the top, as well as replacing with LED bulbs especially in the high-use areas.

I’m also wondering what sort of effect the waste heat from the lighting would have on the HRV system? Given that there’s 21 100W incandescents running for around 8 hours a night with heat being sucked straight up into the roof space, this would surely warm the air in the reasonably well sealed roof space (like having a 2.1KW heater going in the roof space for 8 hours a night) meaning that the HRV would turn on more regularly because there’s a differential between the warm roof space and the colder house that it’s trying to circulate warm air into?

Consequently, the HRV system is likely to be working full time during the lighting period (as well as during solar heating of the roof space). If the homeowner replaces the light fittings with IC-F rated fittings and fixes the insulation gaps, the small amount of waste heat from the LED’s would remain in the room rather than heating up the roof space. Would this not then reduce the amount of time the HRV system is operating because of a lower temperature differential between the roof space and the room(s), saving them money on electricity?

Does anyone have some good technical info on ventilation systems? I’ve had a really good look around online and I can’t seem to find anything that tells me what the power consumption of the fans/heating units/ typical power consumption etc are.

Cheers,
Sarah

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[Ian McChesney]

Hi Phil
Re your HW system I think there are some issues that are impacting on your high power bill, and some that aren’t. The faulty thermostat will be – hotter water will cause higher standing losses from the HW cylinder (maybe an additional 1-2kWh/day), and extra losses associated with the vent pipe, the waste hot water that sits in pipes after hot water is used etc. However, the undersized element, on its own, shouldn’t be adding to power bill. For example, if after a couple of showers the HW cylinder needed to heat 115 litres of cold water up to 60degrees, that would require about 6kWh. A 1.5kW element would take 4 hours to reheat; a 3kW element would take 2 hours. The energy use is the same. Undersized elements tend to add to frustration and poor hot water service rather than the power bill.

If you suspect the element is turning on frequently to maintain temperature it suggests there is excessive heat loss or water loss occurring – poor tank insulation, faulty pressure reducing valve (if fitted), a water leak, or back to the thermostat.
regards
Ian

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[phillcoxon]

Hi Ian,

Thanks for the clarification element heating costs – very helpful.

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[Norman Smith]

Hi Phil, don’t forget the humble hot water cyclinder wrap will save in the order of $1000-1500 over its lifetime; at around $80 to install the cost of generating Negawatts is in the order of 1-2 cents compared to the 28 cents kWhr you pay to buy electrickery.
Norman

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[Scott Willis]

Hi Sarah,
Just as an outlier suggestion – here in Blueskin, where we’ve done a few energy audits prior to HPA’s, two of the things that popped up on the radar are water and waste, because while there’s mostly town supply water, it is trickle feed to a header tank, and in Waitati sewerage is via composting toilets, septic systems or very basic systems. The two issues that have arisen from new builds in this area are:
1. Water pressure pumps – every time the tap is turned on, the pump is engaged to bring water at pressure down the pipe. Would this be an issue in the house too? It always leads to enormous bills and for people who have been made aware of this issue, building a tower with a header tank is usually their first direct project.
2. 24/7 septic tanks. Your clients are probably town sewerage connected, but if not, this one is a biggie.
It does sound as if the house builder has made some energy poor choices in the build and its your (unenviable?) job to inform the current occupants that they can take control, and they can do so in a rational and productive way. Good luck.
Cheers
Scott

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[Sarah Grant]

Hi Scott,

Thanks for weighing in. Some of the first questions I ask in my Home Assessment’s is about the services to the house to make sure I’m fully informed. Even with houses in urban areas I still ask even though it would be reasonable to assume they’re ‘mains’ connected to all services (I’d be pretty embarrassed to miss someone’s PV panels for example!). I specifically checked with this homeowner because in my preparation for the visit I did wonder about this (they’re in a new subdivision in a small village).

The funny thing is, the homeowner I did the assessment for was only the house’s second occupant – it was the builders own home prior to this family. I’d be pretty peeved (with myself) if I built this new gorgeous home and it was cold and expensive to heat. I also suspect strongly that the HRV was installed very early in the house’s life due to condensation problems – but it’s hard to be sure.

Some of you might be interested in this little doozy I found in the roof space – the knot tied in the HRV ducting – presumably to shorten it. Surely this is poor form?

Many thanks for your input, I’ve learnt a lot from this job already and don’t expect it to stop or slow down for a long time yet!

Cheers,
Sarah

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[philgregg]

Hi Sarah

You may be new to this but you ask great question and supply lots of detail. I am a old hat in the field but it is great to get fresh information and perspective to keep us informed. We can get stale. I for one learn something little and new every time. Sorry I haven’t contributed but by the time I get to read them you have had huge amounts of wisdom supplied.

The one thing I can add, not necessarily relevant to your earlier question. White ware is the hidden killer. Lots of people have old fridges and freezer hidden away and they are unaware of the fact they are energy guzzlers

This table will give you some history.

Table 1: Comparison of Energy Consumption of Old and New Refrigerators
Year Refrigerator
Manufactured
Annual Electrical
Consumption
Annual Cost of
Electricity*
1972 2000 kWh $270.00
1990 900 kWh $121.50
1993 690 kWh $93.15
After 2001 485 kWh $65.47
2003 ENERGY STAR
Refrigerator 436kWh $58.86

* Cost of Electricity is calculated at $0.135 per kilowatt-hour, the average cost of
electricity in New York State for residential consumers. Electrical consumption levels
for 1972 – 1993 refrigerators obtained from Lawrence Berkeley Labs Summer 1995

This is an old table so the technology has improved even further. A fridge is the luck a heat pump, where as it uses a compressor. The compressors now used are variable speed which is where the modern efficiency is coming from.

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