Self Build Heating and Cooling Strategy

[Havkey100]

All,

 

PHPP calcs are in and we are firmly in between Passivhaus Plus and Passivhaus Premium by design, less than 0.6ACH, with overheating risk at 1%.  Amazing of course, but the one slight downside of all of this is the multitude of options for heating and ventilation.

 

The solar installation will be 9-13kw of solar (pending DNO approval), a 15kw battery, with no gas installed on site. May consider a V2X Sigenstor as my car has that feature and I have access to  free charging.

 

The basic issue is that we can almost heat the house with a toaster, therefore a heat pump system is for the most part going to provide HW in an unvented cylinder for a family of 5, with only periodic use via a wet U/F loop downstairs on the insulated raft.  The MHVR solution is likely to be a Zehnder Q450.

 

I am trying to weigh up all the permutations we can try in order to minimise capital cost and simplify controls.

 

So far my considerations are:

 

1. MHVR Heating/Partial Cooling with Direct Hot Water Cylinder - £16k

 

• Zehnder Q450 and Comfoclime add on HP, which gives about 2kw of heating and cooling capacity. It comes in at £13k and has the benefit that it likely has all the heating capacity we would ever need, can temper hot conditions (clearly not a full blown AC, but 2kw of cooling would help a lot).
• OSO 300L DHW cylinder. Can heat overnight on an agile tariff, economy 7, and recharge daytime from battery, V2X if needed. £2k installed.
• Contingency install U/F loop in case the above is less liveable than we hope. £1k

 

2. MHVR with 5KW HP HP Cylinder - £18k

 

• Zehnder Q450 £10k
• Vaillant Arotherm 5KW with 300l Vaillant HP Cylinder. £7k out of pocket.
• U/F loop in case the above is less liveable than we hope. £1k

 

3. MHVR with Direct Hot Water Cylinder and IR/Electric Heating - £14.5k

 

• Zehnder Q450 £10k
• OSO 300L DHW cylinder. £2k installed
• Strategic Electric Heating - IR or a few towel rails in the extract locations of the MHVR loop - £1.5k.
• Contingency install U/F loop in case the above is less liveable than we hope. £1k

 

Any other options I am missing here? I am inclined to go with option 1 as it is a bit cheaper, harmonises the controls, and in practice I can't imagine it will cost any more or less in practice to run, plus has some cooling capability. I was also considering the NIBE S735C, but am struggling to lock in pricing on that. I think it may come in at 20k and is an entirely integrated solution from which I could heat via air, u/f, ventilate, cool and manage HW with 300l of storage. But, the issue is the overlap of heating and cooling adds complexity to ownership of an installation between the MHVR designer and heating engineer.

 

Thanks for any input and experience!

 

 

 

[JohnMo]

Keep it all simple and functions separate

 

First ventilation is ventilation, it isn't heating/cooling.  Separate the ventilation keep it a stand alone item. Cooling via MVHR is an expensive folly and in the round doesn't work as flow rates are too low.

 

7 minutes ago, Havkey100 said:

Vaillant Arotherm 5KW

Why oversize the heat pump - bad for SCoP due to cycling. Plus Vaillant don't do cooling out the box and cost way too much

2 minutes ago, Havkey100 said:

almost heat the house with a toaster

So is that 3kW or less? if so heating bey direct electric isn't going to be cheap - 3 x 24 hrs is 72kWh.

 

3 minutes ago, Havkey100 said:

OSO 300L DHW cylinder. Can heat overnight on an agile tariff, economy 7, and recharge daytime from battery, V2X if needed. £2k installed.

Direct cylinder are fine, not sure I would pay the premium for an OSO A rated one.  Slightly oversize for house and heat to 50 degs. Low tariff charge not from battery, use battery for other stuff, not worth the round trip losses when you can charge direct, without going via battery.

 

I would do

Decent no frills MVHR, if you want a Passivhaus certified one, fine, but leave all the optional extras on the shelf

Stand alone small heat pump - A Haier 4kW is £2100 from Wolseley incl VAT (you can reclaim)

Telford Tempest 250L direct cylinder £610

UFH to ground floor, £1k - fully open system, no room stats or actuators, flow direct from ASHP circulation pump

Or direct cylinder and a good quality A2A heat pump for heating and cooling

 

Option 1 - no

Option 2 - no, almost but not quite - £10k for MVHR are you mad?

Options 3 - no

 

[Havkey100]

Thanks, that's why I posted.

 

Agree on HP controls. Have one at the minute and it's unzoned. If I can get that install at less than £5k I'm happy.

 

MHVR seems like it's 4k components, 2k ducting, 4k install, but am working on prices around that. Seems a big racket on it by installers at present.

[JohnMo]

29 minutes ago, Havkey100 said:

MHVR seems like it's 4k components, 2k ducting, 4k install

I installed two units in our house, self installed, well under £2k all in. Ebay can be your friend - if you accept warranty is unlikely.

 

But in the UK you don't need pre heat or enthalpy heat exchangers, you don't need CO2 sensors and really once setup, and running, you don't even need boost very often - we last had boost on (manually) over a year ago, auto boost just isn't activated. Manual boost outside bathrooms and in kitchen, or manual boost in kitchen and humidity activated elsewhere.