Hybrid heating system

[Meabh Kelly]

Hi there

Just starting out on a house build and find there are A LOT of decisions.  Planning permission has been granted but that's as far as I am.

 

I would appreciate some thoughts on heating systems.

 

Plan is a high level of insulation (eg CWI: 150mm thick Kingspan Eco Bead / Quinn lite block, Floor: 100mm foil backed polystyrene) , triple glazing (uPVC frame)  UFH for downstairs and radiators upstairs.    

 

I've considered Heat Pumps but I am being recommended OFCH - specifically Grant Vortex.  In looking at this option I came across Hybrids and wondered if anyone had experience of this: Grant VortexAir Range: https://www.grantuk.com/products/hybrids/?

 

I live in NI so there are no grants available to apply for...

 

Any advice appreciate

 

Meabh

[ProDave]

What has put you off an air source heat pump?

 

The price of oil, while cheap just now is too volatile for my liking. And they are noisy smelly things.

 

I don't think anyone has ever explained how the hybrid combines ASHP / Oil boilers work. how do they handle the transition to ensure you are not just burning oil?  It's hard enough finding someone that understands an ASHP, it must be harder finding someone that understands a particular make of hybrid.

[Bitpipe]

Welcome!

 

Before you plough into heating systems (which, as a NI native I know is close to everyone's heart) have you thought about modelling the performance of the house as a whole (including how it performs in summer), hot water requirements etc to understand what you actually need?

 

If you're going for a good level of insulation you should think on airtightness and also ventilation strategies plus think about how much glazing you have, what the orientation is on the plot, natural and designed in shading etc. 

 

Risk is you could get uncomfortably warm when the sun is shining (even in spring / autumn) even it it's not that hot outside. Even in winter, you may not need as much heating as you think.

 

 

[Meabh Kelly]

7 minutes ago, ProDave said:

What has put you off an air source heat pump?

 

The price of oil, while cheap just now is too volatile for my liking. And they are noisy smelly things.

 

I don't think anyone has ever explained how the hybrid combines ASHP / Oil boilers work. how do they handle the transition to ensure you are not just burning oil?  It's hard enough finding someone that understands an ASHP, it must be harder finding someone that understands a particular make of hybrid.

Nothing has put me off ASHP;  I remain open to options.

 

I thought this might give the best of both worlds but wanted to find out if anyone had experience of it.

 

I am also on a tight budget and noted the OIl boiler can go in with HP added later, if desired

[Meabh Kelly]

9 minutes ago, Bitpipe said:

Welcome!

 

Before you plough into heating systems (which, as a NI native I know is close to everyone's heart) have you thought about modelling the performance of the house as a whole (including how it performs in summer), hot water requirements etc to understand what you actually need?

 

If you're going for a good level of insulation you should think on airtightness and also ventilation strategies plus think about how much glazing you have, what the orientation is on the plot, natural and designed in shading etc. 

 

Risk is you could get uncomfortably warm when the sun is shining (even in spring / autumn) even it it's not that hot outside. Even in winter, you may not need as much heating as you think.

 

 

I am not entirely sure about how to model the performance of the house at the outset but will investigate.

 

Ventilation strategy is a PIV unit as I am an open the windows person all year round.

 

Main living space of the house will get sun throughout the day East through to West and that overheating you mentioned has been in my mind give the East / South corner is double-height window.

 

As an NI native sun and shining is rarely used to describe here; currently it's lashing!!  

[ProDave]

I am willing to bet if you shop around, you will get an ASHP for no more than cost of an oil boiler plus oil tank plus fire valve plus oil pipe etc.

 

Oil boiler needs (or at least should have) annual service. 

 

Just choose over sized low temp radiators upstairs or UFH upstairs, Or like many of us you might find with a well insulated house, no heating is needed upstairs.

 

 

[Meabh Kelly]

1 minute ago, ProDave said:

I am willing to bet if you shop around, you will get an ASHP for no more than cost of an oil boiler plus oil tank plus fire valve plus oil pipe etc.

 

Oil boiler needs (or at least should have) annual service. 

 

Just choose over sized low temp radiators upstairs or UFH upstairs, Or like many of us you might find with a well insulated house, no heating is needed upstairs.

 

 

Thank you, it will be worth considering the costs for both.  

 

I have seen Polar Energi and Mitsubishi Ecodan recommended; are there any particular brands you'd add for consideration?

 

[dpmiller]

You'll need to get a design SAP done for Building Control so that'll be a useful bit of modelling.

[joe90]

I may be wrong but I think the hybrids are to boost the water delivered by the heat pump (fairly low) to “norm” DHW temps. However both @ProDave and myself heat with a heat pump to a temp of 48’ which is enough fir DHW (if you have a slightly larger tank) and way hot enough to blend down fir UFH or straight use with larger radiators. I paid £850 fir my ASHP on Ebay and fitted it myself, it’s only 4kW and we have a 3 bed detached house with “good” insulation levels copied from passive principles but not certified. I would never consider oil after having an ASHP.

[Meabh Kelly]

1 minute ago, dpmiller said:

You'll need to get a design SAP done for Building Control so that'll be a useful bit of modelling.

Yes, I remember that being discussed now...thank you!

 

[Meabh Kelly]

2 minutes ago, joe90 said:

I may be wrong but I think the hybrids are to boost the water delivered by the heat pump (fairly low) to “norm” DHW temps. However both @ProDave and myself heat with a heat pump to a temp of 48’ which is enough fir DHW (if you have a slightly larger tank) and way hot enough to blend down fir UFH or straight use with larger radiators. I paid £850 fir my ASHP on Ebay and fitted it myself, it’s only 4kW and we have a 3 bed detached house with “good” insulation levels copied from passive principles but not certified. I would never consider oil after having an ASHP.

Out of curiosity what make did you get and how long have you had it?

[joe90]

@Meabh Kelly Mine was a “Kingspan “ unit (of the insulation industry) and the reason it was sold off was Kingspan decided not to go into the ASHP market after they launched it, however it is a re badged Carrier unit, and Carrier make millions of air con units and ASHP,s based in the USA. They have a good reputation in the industry. Mine had no warranty but it was still shrink wrapped on a pallet out of the factory so I thought it worth a punt. The only ones to avoid (I have heard) are the non induction ones coming out of China.

[PeterW]

43 minutes ago, Meabh Kelly said:

Thank you, it will be worth considering the costs for both.  

 

I have seen Polar Energi and Mitsubishi Ecodan recommended; are there any particular brands you'd add for consideration?

 

Polar Energi don’t make heat pumps - they make cylinders. They use Panasonic ASHP external units. 
 

Both Mitsubishi and Panasonic are decent brands so either is fine. 

[ProDave]

42 minutes ago, joe90 said:

I may be wrong but I think the hybrids are to boost the water delivered by the heat pump (fairly low) to “norm” DHW temps. However both @ProDave and myself heat with a heat pump to a temp of 48’ which is enough fir DHW (if you have a slightly larger tank) and way hot enough to blend down fir UFH or straight use with larger radiators. I paid £850 fir my ASHP on Ebay and fitted it myself, it’s only 4kW and we have a 3 bed detached house with “good” insulation levels copied from passive principles but not certified. I would never consider oil after having an ASHP.

My issue is HOW does that work?  It would have to rely on the return temperature being very low, so the ASHP could heat it first then the oil boiler top it up.  That would imply a very low flow velocity, which is exactly what an ASHP does not like.

 

My concern is the ASHP would only end up working in the initial stages of heating and once up to temperature the oil burner would be doing it all.

 

I would love to hear how these work in practice.

 

Regarding which heat pumps to avoid.  Just make sure it is INVERTER driven, so it can modulate it's power to the actual load.

[jamieled]

I was speaking to a plumber about the oil-ashp hybrids the other day. Apparently the grant ones figure out what the most financially optimal source  is to use based on heat pump CoP and delivered oil/electric price. They only use one or the other source at any one time.

Other hybrids might work differently though.

[Temp]

1 hour ago, joe90 said:

I may be wrong but I think the hybrids are to boost the water delivered by the heat pump (fairly low) to “norm” DHW temps.  

 

I had a look in the manual and it might be more sophisticated.. 

 

The oil boiler will only be operated when the ambient air temperature falls to a level where the heat pump cannot either sustain the  required flow temperature for the system, or when the heat demand cannot be met by the heat pump at the set flow temperature.

 

 

 

[Meabh Kelly]

1 hour ago, PeterW said:

Polar Energi don’t make heat pumps - they make cylinders. They use Panasonic ASHP external units. 
 

Both Mitsubishi and Panasonic are decent brands so either is fine. 

Thank you...from another group Mitsubishi seems to be very popular in Ireland as a whole. 

[Meabh Kelly]

1 hour ago, jamieled said:

I was speaking to a plumber about the oil-ashp hybrids the other day. Apparently the grant ones figure out what the most financially optimal source  is to use based on heat pump CoP and delivered oil/electric price. They only use one or the other source at any one time.

Other hybrids might work differently though.

I'll definitely investigate this further, thank you

[dpmiller]

Some heatpumps have built-in control for the boiler using similar strategy. The Peak/ Lailey and Coates unit for example.

[Alexphd1]

I like ashp's, I like oil boilers but I fail to like the idea of combining the two systems together. Sounds like the control system could be a pain in the ass to mantain/repair further down the line. I would keep the system as simple as possible (although I have failed on that with our hybrid system). 

 

Have you seen the price of the vortex air unit? 

Edited July 5, 2020 by Alexphd1

[SteamyTea]

16 hours ago, ProDave said:

I don't think anyone has ever explained how the hybrid combines ASHP / Oil boilers work.

The way I understand it is that the oil part is comparable to the resistance heater in a regular ASHP.

So if sized correctly, the ASHP does most of the work with the oil burner just being used for boosting DHW temperature and the occasional times that the ASHP is unable to deliver enough space heating.

Seems a lot of hardware for little work.  But I suspect the ASHP element is used to tick an 'environmental' box is too small for most houses.

[ProDave]

2 hours ago, SteamyTea said:

The way I understand it is that the oil part is comparable to the resistance heater in a regular ASHP.

So if sized correctly, the ASHP does most of the work with the oil burner just being used for boosting DHW temperature and the occasional times that the ASHP is unable to deliver enough space heating.

Seems a lot of hardware for little work.  But I suspect the ASHP element is used to tick an 'environmental' box is too small for most houses.

But I turned off the resistance heating function in my ASHP because I could see the flaw.  It did something like heat the water to 45 degrees with the ASHP then heat it further to 55 degrees with the built in willis heater.

 

The "issue" was as the water cooled down, the temperature sensor would say it's gone below 55 degrees by it's hysteresis setting and turn on the willis heater. It rarely went low enough to trigger the ASHP to "pre heat" it, unless you ran off the whole tank of water in one go.

 

I now heat it to 48 degrees just with the ASHP function.

[dpmiller]

certainly L&Cs take on hybrid is to switch from ASHP to the other boiler when ambient temp crosses a set point, it's configurable with DIP switches  to temps betwen +5 and -5C. Presumably they reckon that the COP loss plus defrost cycling means the alternative fuel is cheaper in those circumstances.

[Meabh Kelly]

On 05/07/2020 at 21:35, dpmiller said:

Some heatpumps have built-in control for the boiler using similar strategy. The Peak/ Lailey and Coates unit for example.

Thank you for the ideas