Heat pump hydronics

Hi there,
We are doing a major renovation and extension on our weatherboard cottage in the Dandenong Ranges, which has a tin roof and is raised up on stumps. Once completed the house will be insulated all round, with double glazed windows.
We want to install hydronic radiators but have no gas to the property, so will use a heat pump. The problem we're having is that we've been to multiple suppliers and installers around Melbourne and have been getting grossly different quotes and advice about the size of panels we will require. We're also getting very different advice about the wisdom (or not) of combining our hydronics and domestic H2O using a separate coil tank attached to the heat pump.
We've looked at woodfired hot water and solar already but neither is really feasible for our location and lifestyle.
So am wondering if anyone here has recent experience with installing a heat pump radiator panel hydronics system in Melbourne, and would be willing to share that experience? It's been a very confusing process and it's expensive, so we want to get it right!
Thanks in advance,
Kate

Wrote a big post, lost it when the website refreshed, which happens often. Hate this site on mobile, so visit it less frequently...... End rant!

So a brief recap. I'm no expert.

Heat pumps lose efficiency the higher the required output temperature. Hydronic radiators require a substantially higher water temperature than hydronic floors. I love the idea of using heat pumps instead of gas, but I'm not too sure how well a heat pump will work with radiators, especially if it gets cold at night where you are.

One way to lower the required water temperature for radiators is to oversize the panels. I'm not sure how much this reduces the required water temperature (or improves the efficiency of the heat pump), or how large the panels need to be.

The other option may be to look at a hydronic floor, if the heat pump will be more efficient. There's interesting products now for use with timber floors, or screeds. Not sure if they'd work well for a renovation, & also not sure if they require higher water temperatures than the usual hydronic floor (high thermal mass concrete floor).

Edit: grrr, even my edits get refreshed & lost. Crappy site mods!

Domestic hot water: requires slightly lower output temps than hydronic panels, much lower than (high mass) hydronic floors. But heat loads for any hydronic system will be much, much higher than the domestic hot water. Hence why solar thermal (panels or vacuum tubes) are a bad idea to heat hydronics. They are expensive & struggle to heat domestic water in winter, they'd have very, very little hearing effect on hydronics. You'd have to cover the roof, a very very expensive exercise. A much better idea to put a large (6.6kW) solar PV system on the roof, to power your heart pump & other electrics.

Hi, thanks for responding. We have done a lot of research into this area, and know the panels need to be larger due to the temperature limitations of the heat pumps. One thing we're fielding discrepancy on from suppliers is HOW large the panels need to be. It's very hard to get a straight answer. I guess what we're hoping to find out is whether someone has actually installed heat pump hydronics and found that it works, and perhaps if they can recommend a supplier? Thanks! Kate

Hi Ddarroch,

Thank you for bringing this to our attention and apologies for the hindered experience.

I was not aware of this and it is quite disheartening to learn that new and loyal members have been experiencing this for some time.

I have forwarded this to our programmer whom is overseas at this moment in the hope he can rectify this shortly.

I’ll keep you posted.

In the interim, please send any further details pertaining to this issue via PM, at least until posting functionality is working as intended.

Regards,

Jason

[quote="homeone":11uess1m][quote="ddarroch":11uess1m]Wrote a big post, lost it when the website refreshed, which happens often. Hate this site on mobile, so visit it less frequently...... End rant!

Edit: grrr, even my edits get refreshed & lost. Crappy site mods![/quote:11uess1m]

Hi Ddarroch,

Thank you for bringing this to our attention and apologies for the hindered experience.

I was not aware of this and it is quite disheartening to learn that new and loyal members have been experiencing this for some time.

I have forwarded this to our programmer whom is overseas at this moment in the hope he can rectify this shortly.

I’ll keep you posted.

In the interim, please send any further details pertaining to this issue via PM, at least until posting functionality is working as intended.

Regards,

Jason[/quote:11uess1m]
Hi Jason,

Sorry for the rude rant. Just a bit infuriating writing long posts, which is quite difficult on a mobile device, only to lose them.

Didn't know this bug was unknown, partly my fault for not reporting it. Best of luck resolving the issue.

Thanks,
David

Thankfully, our programmer was able to get onto this from overseas.

Again, immense thanks for your welcome feedback and going forward please communicate any bugs, or suggested improvements to me directly via PM so they’re not missed and so we act on these as quickly as possible.

We understand there are some remnant quoting issues on the site which our programmer will look at next week upon his return.

Hi Kate,
I read your post and was wondering how you went? With panel sizing, it ultimately comes down to understanding what your building’s heat load is. Many suppliers/ trades use rule of thumbs to estimate the various room heating loads. This approach is a bit like using a blunt instrument to cut - it’s a bit rough!! And given you’re looking to use a heat pump, getting the heat load calculation accurate is important to prevent under or over sizing.

Calculating a building’s heat load can get quite complex. Software makes it easier and I would suggest an App by Carmelsoft called “HVAC Residential Loads” https://www.carmelsoft.com/iOS_Mobile_S ... for_iPhone. Only challenge with this, is understanding how to apply the R-values which are US based so you’ll need to convert from imperial to metric, http://www.myonlinediary.com/index.php/ ... tionTables

Once you understand the heat loads for each room, you can then size the radiator panels based on a nominal design flow and return temperature - typically 55/ 45 and desired room temperature. A free calculator you can use for this is the “Henrad Radiator Heat Load Calculator” https://www.hydroheat.com.au/news/radia ... ator-tool/

The overall heat load of your radiators should closely match your heat pump capacity. Out of curiosity, what heat pump have you decided on?

Cheers
Graham