Ventilation system or replacement heat pump?

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Smix

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#2023972 28-May-2018 14:39

Thanks for the continued discussion! I forgot to mention we also have the poly lining under the house as well.

It sounds like having a crack with a panel heater and possibly a dehumidifier might actually be a significantly cheaper alternative. I've just got back from Noel Leeming and they've given $850 as an estimate for install of a heatpump, which is already almost twice as much as a panel heater + dehumidifier combo. This fiscally rules out getting a heatpump for just the bedroom.

@mdf yep definitely agree that I wouldn't want Bubs relying on white noise, however, I think running the dehumidifier while she's not in the room might be a good compromise. Your comment, " We went through a similar thing - old draughty damp first home, mortgage, a new born, and down to one income", perfectly describes our position. Due to my wife having ongoing issues with her mental health (bipolar depression) she hasn't been working for a couple of years, and there is no expectation for her to go back (I'd rather have a happy wife!!!). This is also why I don't want to draw any more funds from the mortgage than necessary. The panel heater + dehumidifier also means I'm not using borrowed funds to pay for it.

@Aredwood I actually came across a GZ thread where they talked about DIY maintenance on heatpumps. Managed to do a thorough clean earlier today and she seems to be running a bit better - there was quite a bit of dust build up in the filters.

Thank you again everyone!

TLD

902 posts

Ultimate Geek

#2024072 28-May-2018 17:59

My understanding is that heatpumps have come a long way over the years, and are more efficient now. We have just had both of our heat pumps replaced in our 20 year house, and were advised to go large, as a more powerful heat pump ticking over, is less costly to run than a less powerful heat pump running flat out trying to keep up.

So we have a 5.5Kw wall mounted heat pump in the bedroom, and a huge 13.5Kw ducted heat pump for the est of the house. It's early days yet, so we have not worked out how much it is costing us to run, but by heck, the big one soon warms up the house.

Trevor Dennis
Rapaura (near Blenheim)

Aredwood

3885 posts

Uber Geek

#2024324 28-May-2018 22:08

TLD:
My understanding is that heatpumps have come a long way over the years, and are more efficient now. We have just had both of our heat pumps replaced in our 20 year house, and were advised to go large, as a more powerful heat pump ticking over, is less costly to run than a less powerful heat pump running flat out trying to keep up.

So we have a 5.5Kw wall mounted heat pump in the bedroom, and a huge 13.5Kw ducted heat pump for the est of the house. It's early days yet, so we have not worked out how much it is costing us to run, but by heck, the big one soon warms up the house.

5.5 KW of heating in a bedroom, how big is your bedroom? I'm currently managing with a 1KW electric heater in my bedroom in Auckland. And there is no insulation at all. (difficult but not impossible to install insulation). I eventually want to get a heatpump for that room. But the smallest one I have found has a min heat output of 0.7KW (Panasonic Z20-TKR) And that still has a rated output of 2.7KW Which will be plenty even without any insulation. And after the insulation is installed, less heat will be needed. And importantly it has a COP of 5. So it is very efficient.

Only reason I can see for such a big heatpump in a bedroom is for dealing with a high summer cooling load. The above heatpump won't be enough for daytime summer cooling as my bedroom gets excellent afternoon sun. But I don't care about that. Summer nighttime cooling load is far lower due to no sun. The 4KW version of the above Panasonic heatpump has a COP of 3.93 in comparison. So you are taking a 20% efficiency reduction by buying a bigger than necessary heatpump. And if you will be mostly leaving it on all the time over winter, it will be unlikely to ever need to ramp up to max output. And a smaller capacity heatpump can be cheaper to install, as the lower peak power draw means that it can be connected to an existing power point circuit. Instead of needing a new cable back to the switchboard.

timmmay

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#2024377 29-May-2018 07:09

I use a 1000W oil heater in the bedroom, only turned on 1/3. In the middle of winter I use two of them, not for total output but for heat distribution.

Hammerer

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#2024704 29-May-2018 12:40

Smix:

@mdf yep definitely agree that I wouldn't want Bubs relying on white noise, however, I think running the dehumidifier while she's not in the room might be a good compromise. Your comment, " We went through a similar thing - old draughty damp first home, mortgage, a new born, and down to one income", perfectly describes our position. Due to my wife having ongoing issues with her mental health (bipolar depression) she hasn't been working for a couple of years, and there is no expectation for her to go back (I'd rather have a happy wife!!!). This is also why I don't want to draw any more funds from the mortgage than necessary. The panel heater + dehumidifier also means I'm not using borrowed funds to pay for it.

We chose to have one of us at home until our kids left school so had similar decisions to make which means getting the biggest bang for our buck. As expected, insulation gave us the best return. We found that after insulating the ceiling and floor that doubling curtains worked great - you can buy them cheaply second-hand particularly for backing where you don't care so much about the colour - extending them to the floor and even further across the wall if the walls have no insulation.

I hadn't heard that white noise is habitual/addictive. What's the evidence for this? I work with babies and preschoolers and I've only ever seen one who relies on having white noise outside of the house.

Hammerer

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#2038061 15-Jun-2018 09:50

Hammerer:

timmmay:

I'm not sure that a dehumidifier is a great investment. Yes they reduce moisture which makes it cheaper to heat the place (a little), but IMHO if there's enough of a problem to need one it's better to put in a long term solution, such as extractors in bathrooms and kitchens, plastic under floor to stop rising damp, and eventually a ventilation system if required.

...

How much does it reduce heating costs? One-off heating of 1 litre of water by 1C takes .001172 kWh. That doesn't seem much but over 24 hours assuming a temperature drop of 1C per hour without heating then it would only take 3-4 days to save a kWh.

If my Goldair GW330 dehumidifier runs continuously and removes 4 litres a day (it can get up to 8) then it would take less than a day to save 1kWh of heating. At 25c/kWh for 100 days a year then I'd save about $25-50 a year on a heating spend of $390 resulting in a 6-13% saving. That's not too bad on a $250-300 sale purchase. Plus that's only to maintain 1C/hour of heat loss. In practice, winter heat losses are usually much higher than that.

I've realised that I underestimated the savings from running a dehumidifier. Since we've been running our dehumidifier 24x7 in the hallway at the centre of the house, we've gained far greater benefit than we expected: we feel a lot warmer and have almost no condensation on the bedroom windows. In the past we used a 700 watt heater for the same purpose and got a lot less heating. So that made me reconsider the numbers because of the noticeable improvement in temperature and comfort.

Our dehumidifier running on the lowest (and quietest) setting is using less than 0.5kW/hr to remove about 4 litres of water a day.

We gain at least a 3C rise in temperature and we save a further 0.33 kWh/day (= 3C x 4L x 24h x 0.001172kWh) on heating the water that was removed.

The greater benefit is largely explained by accounting for the enthalpy of condensation (or latent heat of condensation/vaporisation) of water. At 12C it is 0.687 kWh/kg (for water it is the same kWh/l) so every 4 litres removed by the dehumidifier will give me an additional 2.75 kWh of heat each day.

In total, we gain additional heating of about 3kWh per day (= 2.75 + 0.33) on expenditure of about 12kWh which results in a 25% additional benefit over a heater. So we're spending $1.80 (12kWh) a day to get $2.25 (15kWh) of heating (at our GST inclusive variable rate for electricity of 15c/kWh with Flick).

Over 100 days we are actually saving at least $45. That is less than 7 years payback for the dehumidifier. If we were paying 25c/kWh then we would be saving $75 a year and payback would be 4 years.

Incidentally, Harvey Norman have a different dessicant dehumidifier on sale, the Dimplex 9L Desiccant Dehumidifer (GDDEKD9) which is a little smaller, has a 5l tank (c.f. 2l), extracts an additional 1L/day, indicates actual humidity level, has an air deflector to vent the air horizontally rather than directly upwards, has a carbon filter, and has a timer (1-24 hour). But it is a bit more expensive (sticker price and replacement filters) and is slightly heavier at 7.5kg.

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