What does the forum think of heat pumps?

[contadino]

What's an MHRV?

Mechanical heat recovery ventilator. Pulls warm air from the house and runs it through a heat exchanger pulling cooler air from outside. Doesn't aim to concentrate heat, just not lose it.

 

[Drago]

Been researching this. It is very plausible, and when in and operating its cost effecting, relatively green heat.

Downsides are is the expense installation, and the need for roughly double the amount of radiator area to heat a room to the same temperature as a gas boiler, and thats with ground source.

I wouldn't dismiss the idea, although it appears better suited to a house in the design stage where everything can be better incorporated, particularly the extra rads.

 

[TheDoctor]

They're pretty much the standard in NZ. Certainly where we were, it worked well for both heating and cooling.

 

[Yellow Fang]

I just read that the sale of gas boilers will be banned from 2025, so it looks like we will have to get used to heat pumps.

I don't have central heating in my flat. I only have a gas fire in my lounge, which I don't use much. I have an electric fan heater, which I also don't use much. For hot water I have an electric shower, and two electric water heaters for the bathroom and kitchen sinks.

In the Orkneys I met someone who had an air-to-air heat pump. The Orkneys are not on the gas grid. It looked quite switch-on-and-offable, which a lot of heat pump systems are not. Hotel rooms often have them too, sometimes combined with air conditioning systems. They don't do hot water though. I wondered whether an air-to-air heat pump that directs warmth to where you are via ducting might be an idea.

 

[numbnuts]

I live in housing association, they are thinking about electric water boilers when the gas ones need replacing, heating is going to be bloody expensive in years to come, more so for older homes.

 

[byegad]

The second law of thermodynamics, aka "you can't move heat from a cooler to a hotter".
Ultimately, no amount of pipework routing trickery can avoid this.

A fridge does.

 

[yello]

I sometimes wonder if ground source vs air source is a case of the excellent being the enemy of the good enough. People who are interested in it read that ground source heat pumps are better, find out it's more expensive and/or requires digging up your garden. but don't want air source because it's second best, then lose interest.

I think that's a pretty fair assessment.

We looked at ground source - it was not just expensive but cost uncertain/open. There's a lot of granite in our area so installers couldn't guarantee costs of sinking the borehole. We then looked to air source but I was less than convinced as to their effectiveness. Sure, they use them in Scandinavia (cold countries) but the houses there tend to very well insulated too. Air source might be okay for under floor heating in a well insulated house but I didn't feel it was our answer.

We opted for wood pellet in the end. Not super cheap, neither outlay nor running costs, but does the job well enough. It runs rads, underfloor heating and provides hot water. I also spent a fair amount on insulation. Bang for buck, it was probably that that was the most effective spend.

 

[JhnBssll]

As junior mechanical building services engineers we were taught that conventional radiators are designed to run with a ~60 degree differential between flow and return. Heat pumps on the other hand produce a much lower flow temperature and therefore a lower differential so it's not as simple as removing a boiler and plumbing in a heat pump which to date has minimised their use. The lower flow temperatures are much better suited to underfloor heating, where you're essentially heating the fabric of the building which then heats the air within in, rather than the other way round with radiators. Underfloor systems run by heatpumps in well insulated buildings will run almost constantly at a low output to maintain a steady temperature, unlike a boiler which will fire in short bursts causing the air temperature to fluctuate slightly throughout the day. The downside is not many people are prepared to dig their floor up, and first floor installation in existing buildings can be irksome. This was true 15 years ago anyway, the technology has no doubt come on but I suspect the limitations remain.

Part L of the building regs are constantly being updated and will almost certainly ban the installation of gas and oil boilers in new builds within the next few years. This will likely improve the cost of heat pump installation in new builds, but is unlikely to have much effect on retrofit costs in the short term. My understanding is that gas and oil boilers will still be available as a replacement in homes already heated by these means, otherwise we'd all have a bit of a problem on the horizon

If I were building a new home now it would be super insulated on the outside with a high internal thermal mass, underfloor heating via ground source heat pump and PV panels on the roof to offset the running costs Combined with heat recovery ventilation and clever design to minimise the heating effect of the sun through windows and you've got yourself a comfy home with minimal energy use. In theory at least Controlling moisture is a challenge as the building has to be basically sealed to work properly so the ventilation design is critical, especially around showers, hobs etc where large amounts of steam are generated.

This answer is much longer than expected, sorry In response to the original question, they're great in the right circumstances but not really suitable for many existing buildings without significant outlay.

 

[yello]

Oil boilers have been phased out/banned already in France, from next year I believe. You can still have one, of course (you don't need to remove it) but you can't install a new one and I don't believe you can get one repaired either, not legally anyway. The latter is obviously going to be a bit of a grey area since plumbers will do cash jobs, and there will be stocks of spares sitting on shelves - and, of course, not everyone has the ready cash to stump up for a new heating system.

There's been a big govt push of later to get people on to more 'eco' forms of heating, with all manner of grants, loans and tax incentives over the years. Air heat pumps are part of that push and are very popular - perhaps even the default option for new builds - and the sight of the units fixed to the side of houses (new and old) is not at all uncommon.

 

[BrumJim]

As junior mechanical building services engineers we were taught that conventional radiators are designed to run with a ~60 degree differential between flow and return. Heat pumps on the other hand produce a much lower flow temperature and therefore a lower differential so it's not as simple as removing a boiler and plumbing in a heat pump which to date has minimised their use. The lower flow temperatures are much better suited to underfloor heating, where you're essentially heating the fabric of the building which then heats the air within in, rather than the other way round with radiators. Underfloor systems run by heatpumps in well insulated buildings will run almost constantly at a low output to maintain a steady temperature, unlike a boiler which will fire in short bursts causing the air temperature to fluctuate slightly throughout the day. The downside is not many people are prepared to dig their floor up, and first floor installation in existing buildings can be irksome. This was true 15 years ago anyway, the technology has no doubt come on but I suspect the limitations remain.

Part L of the building regs are constantly being updated and will almost certainly ban the installation of gas and oil boilers in new builds within the next few years. This will likely improve the cost of heat pump installation in new builds, but is unlikely to have much effect on retrofit costs in the short term. My understanding is that gas and oil boilers will still be available as a replacement in homes already heated by these means, otherwise we'd all have a bit of a problem on the horizon

If I were building a new home now it would be super insulated on the outside with a high internal thermal mass, underfloor heating via ground source heat pump and PV panels on the roof to offset the running costs Combined with heat recovery ventilation and clever design to minimise the heating effect of the sun through windows and you've got yourself a comfy home with minimal energy use. In theory at least Controlling moisture is a challenge as the building has to be basically sealed to work properly so the ventilation design is critical, especially around showers, hobs etc where large amounts of steam are generated.

This answer is much longer than expected, sorry In response to the original question, they're great in the right circumstances but not really suitable for many existing buildings without significant outlay.

Thank you for that. Very interesting.

 

[Deleted member 26715]

Would you get one? If so, what sort? If not, what puts you off?

The sales guy, all he is interested in is signing up up for the loan so he gets his commission, same as if you enquire about solar panels.

 

[Yellow Fang]

As junior mechanical building services engineers we were taught that conventional radiators are designed to run with a ~60 degree differential between flow and return. Heat pumps on the other hand produce a much lower flow temperature and therefore a lower differential so it's not as simple as removing a boiler and plumbing in a heat pump which to date has minimised their use. The lower flow temperatures are much better suited to underfloor heating, where you're essentially heating the fabric of the building which then heats the air within in, rather than the other way round with radiators. Underfloor systems run by heatpumps in well insulated buildings will run almost constantly at a low output to maintain a steady temperature, unlike a boiler which will fire in short bursts causing the air temperature to fluctuate slightly throughout the day. The downside is not many people are prepared to dig their floor up, and first floor installation in existing buildings can be irksome. This was true 15 years ago anyway, the technology has no doubt come on but I suspect the limitations remain.

Part L of the building regs are constantly being updated and will almost certainly ban the installation of gas and oil boilers in new builds within the next few years. This will likely improve the cost of heat pump installation in new builds, but is unlikely to have much effect on retrofit costs in the short term. My understanding is that gas and oil boilers will still be available as a replacement in homes already heated by these means, otherwise we'd all have a bit of a problem on the horizon

If I were building a new home now it would be super insulated on the outside with a high internal thermal mass, underfloor heating via ground source heat pump and PV panels on the roof to offset the running costs Combined with heat recovery ventilation and clever design to minimise the heating effect of the sun through windows and you've got yourself a comfy home with minimal energy use. In theory at least Controlling moisture is a challenge as the building has to be basically sealed to work properly so the ventilation design is critical, especially around showers, hobs etc where large amounts of steam are generated.

This answer is much longer than expected, sorry In response to the original question, they're great in the right circumstances but not really suitable for many existing buildings without significant outlay.

That's the thing with these big, complex systems. They are alright for new builds. However, the government seems to have a one size fits all approach to heating buildings.
A system like the one you described:

• is on all the time - I am not in much of the time.
• heats all the house - I don't need all my flat heated.
• heats water tank- I don't use that much hot water.
• controls air moisture - just not a problem for me really.
• works best with a highly insulated building - my flat has solid walls, sash windows and no access to the roof space.
• has a heat recovery ventilation system - what if it breaks down? Someone installed an extraction fan in my bathroom years ago. Now it is just a hole in the wall.

 

[JhnBssll]

That's the thing with these big, complex systems. They are alright for new builds. However, the government seems to have a one size fits all approach to heating buildings.
A system like the one you described:

• is on all the time - I am not in much of the time.
• heats all the house - I don't need all my flat heated.
• heats water tank- I don't use that much hot water.
• controls air moisture - just not a problem for me really.
• works best with a highly insulated building - my flat has solid walls, sash windows and no access to the roof space.
• has a heat recovery ventilation system - what if it breaks down? Someone installed an extraction fan in my bathroom years ago. Now it is just a hole in the wall.

I don't disagree, and that is sort of my point - these new systems are excellent in a new build that's properly maintained. They're not so great when bits of it are installed in older properties without properly considering the knock-on effects.

Regarding controlling moisture, you won't have a problem because old buildings are not even close to airtight. It becomes a problem when you seal the space up in order to prevent heat loss, which then has to be solved with mechanical ventilation. Heat recovery units are pretty simple devices, just a pair of fans, a filter and a plate to plate heat exchanger, but the filters will need cleaning periodically and the fans will have a design life so you're right, they're not fit and forget...