What am I looking for ?

[Nic]

Hi 

looking at an ASHP for a small ( total 110m2 two story build . I will need it just to run UFH  on ground floor and DHW  . But I’d like it to do cooling as well ? 
the how will be passive based , airtight well insulated etc probably 6kw or 8kw ( probably still over kill… not got calculations back from architects yet) will obviously need a DHW cylinder as well and will want to run in conjunction with solar panels on the roof… are certain ashp’s better at cooling as well as heating… sorry bit of a novice 

[jack]

22 minutes ago, Nic said:

are certain ashp’s better at cooling as well as heating… sorry bit of a novice 

 

I don't recall there being a particularly big difference between brands that offered cooling, but I last properly looked when I bought mine ~9 years ago!

You might want to see how the ones you're looking at allow cooling mode to be enabled. In my case (Panasonic from 9 years ago), it was just a case of entering a sequence via the control pad. At least one manufacturer requires you to buy a module that plugs into the unit. After some investigation, it was found that the module (over £100, from memory) contained a resistor worth a few pence. Worse (or maybe better, depending upon your perspective!), the exact same module is used by the same manufacturer for another purpose and is sold for a few percent of the price for that purpose.

[JohnMo]

So heat loss first. More likely the smallest heat pump you can get (around 4kW). Panasonic seem good (I don't have one, but everything I have read seems that way)

 

You size the cylinder is based on the number of bedrooms and likely people living there. Our 3 bed has a 210L. Get a cylinder with at least 3m² coil, for heating efficiency.

 

Cooling - matter of finding which do it. Panasonic do it out the box.

 

Keep it simple, less outlay, easy to run, best efficiency.

 

 

[MPH243]

If your house is near passive it will be small.  Don't bother to individual zone just one. 

 

We have a 8.5kw and 260sqm, better than the old building regulations for insulation just under 2 for air tightness. It has easily coped with our heating demand in mid Devon. 

I need to get mine to cool as overheating in summer is not so nice. 

Don't bother trying to get your mvhr to cool. 

[Nic]

9 hours ago, MPH243 said:

If your house is near passive it will be small.  Don't bother to individual zone just one. 

 

We have a 8.5kw and 260sqm, better than the old building regulations for insulation just under 2 for air tightness. It has easily coped with our heating demand in mid Devon. 

I need to get mine to cool as overheating in summer is not so nice. 

Don't bother trying to get your mvhr to cool. 

Why not to bother with the MVHR to do some cooling ? 

[nod]

9 hours ago, JohnMo said:

So heat loss first. More likely the smallest heat pump you can get (around 4kW). Panasonic seem good (I don't have one, but everything I have read seems that way)

 

You size the cylinder is based on the number of bedrooms and likely people living there. Our 3 bed has a 210L. Get a cylinder with at least 3m² coil, for heating efficiency.

 

Cooling - matter of finding which do it. Panasonic do it out the box.

 

Keep it simple, less outlay, easy to run, best efficiency.

 

 

Our neighbor is on there nineteen year with a Panasonic Which is sited on a flat roof Very exposed So you have longevity with this brand 

We had three quotes and all where against cooling and advised a small air on unit 

[Nic]

4 minutes ago, nod said:

Our neighbor is on there nineteen year with a Panasonic Which is sited on a flat roof Very exposed So you have longevity with this brand 

We had three quotes and all where against cooling and advised a small air on unit 

Did they say why no cooling ? 

[JohnMo]

16 minutes ago, Nic said:

Why not to bother with the MVHR to do some cooling ? 

Because it can't do it very well and it isn't cheap. I worked out our near 200m² house on normal MVHR flow rates, MVHR colling would deliver around 1kW if heating. The ASHP flow temp was 7 degs. Our floor can deliver 4x that at 14 Deg flow temp.

[ReedRichards]

30 minutes ago, Nic said:

Did they say why no cooling ? 

1. Technically, you have to be careful about condensation
2. Administratively, an ASHP installed as a retrofit does not usually require Planning Permission if only used for heating, but it does need Planning Permission if it is also used for cooling.

Those are my guesses.

[nod]

1 hour ago, Nic said:

Did they say why no cooling ? 

All sited condensation as an issue 

All said the benefits of cooling are quite small All where quoting for Mitsubishi Eco 

 

 

[PhilT]

There is a balance to be struck between the desire to achieve maximum efficiency from a smaller unit and minimising the time your heating is off while the DHW cycle is going, especially in the depths of Winter, and taking into account regular defrost cycles. My son's passivhaus is 150sqm and the heat loss calcs suggested a 5kW ASHP but he went for a 7kW ASHP so his DHW tank would heat up quicker for a family of 4 regular hot water users.

 

A 200 litre tank if heated by a 4kW source would take 1 hour and 45 minutes to get from 20 to 50degC. 7kW brings that down to under 1 hour.

 

My view, for what it's worth, is that you should go for a minimum of 6kW, because modern heat pump software manages the system to avoid cycling and maximise efficiency no matter how oversized for central heating purposes, up to a point of course. Case in point - I have an 11.2kW heat pump which is at least 50% oversized but is achieving SCOP of 4.2 with a microbore fed radiator system. And my hot water heats up very quickly!!!

[Nic]

1 hour ago, JohnMo said:

Because it can't do it very well and it isn't cheap. I worked out our near 200m² house on normal MVHR flow rates, MVHR colling would deliver around 1kW if heating. The ASHP flow temp was 7 degs. Our floor can deliver 4x that at 14 Deg flow temp.

So best option ashp for UFH ( and a bit of cooling) and DHW . MVHR to just do its thing , cylinder that has min3m3 coil and can run via ashp and solar and fan coils for bedrooms  how do they work please? 

[JohnMo]

20 minutes ago, PhilT said:

200 litre tank if heated by a 4kW source would take 1 hour and 45 minutes to get from 20 to 50degC. 7kW brings that down to under 1 hour.

But that is only really true for the first heat cycle, after that it's only heating the bottom third in reality. My 210L has never taken more than 45 mins to heat with a 6kW.

 

24 minutes ago, PhilT said:

because modern heat pump software manages the system to avoid cycling and maximise efficiency no matter how oversized

Look at the many threads on different forums where cycling is an issue. You can manage cycling but it doesn't generally happen out the box. Certainly not as left by many installers. Samsung requires use of the controller thermostat and water law together, to add more hysterisis to the heating system, mine required the hysterisis setting moving a long way from manufacturer setting, some heat pumps use good controls that make sure cycling is acceptable as a default setting - many don't.

[JohnMo]

10 minutes ago, Nic said:

So best option ashp for UFH ( and a bit of cooling) and DHW . MVHR to just do its thing , cylinder that has min3m3 coil and can run via ashp and solar and fan coils for bedrooms  how do they work please? 

Fan coil is similar to the heater in your car, a heater matrix and fan to blow air through the matrix. The water can be a fixed or variable temperature and fan speed moves to get the heat out of the heater. In cooling mode you supply with cooled water and it blows out cold air not hot.

[ReedRichards]

One thing you have to be careful about when determining the optimum size of your heat pump is software limiting.  I believe it's quite common for a manufacturer to sell the same heat pump as, say, a 4 kW , 6 kW and 8 kW model where the only difference is a software-imposed maximum.  In which case there is no disadvantage to getting the highest power model as all three will have the same minimum power.    

[Nic]

50 minutes ago, PhilT said:

There is a balance to be struck between the desire to achieve maximum efficiency from a smaller unit and minimising the time your heating is off while the DHW cycle is going, especially in the depths of Winter, and taking into account regular defrost cycles. My son's passivhaus is 150sqm and the heat loss calcs suggested a 5kW ASHP but he went for a 7kW ASHP so his DHW tank would heat up quicker for a family of 4 regular hot water users.

 

A 200 litre tank if heated by a 4kW source would take 1 hour and 45 minutes to get from 20 to 50degC. 7kW brings that down to under 1 hour.

 

My view, for what it's worth, is that you should go for a minimum of 6kW, because modern heat pump software manages the system to avoid cycling and maximise efficiency no matter how oversized for central heating purposes, up to a point of course. Case in point - I have an 11.2kW heat pump which is at least 50% oversized but is achieving SCOP of 4.2 with a microbore fed radiator system. And my hot water heats up very quickly!!!

thanks that’s great . We are only 110m2 split evenly over two floors ( two double en-suites upstairs)  mostly open plan down stairs . So 6kW would be good ( three of us ) 👍🏼

[Dave Jones]

1 hour ago, nod said:

All sited condensation as an issue 

All said the benefits of cooling are quite small All where quoting for Mitsubishi Eco 

 

 

 

bit like saying a combi is better as you dont need to bother insulating.

 

ASHP for cooling is new, the MCS 'professionals' are not done ripping people off for heating let alone not being able to rip them off for 2 ASHP one for heating and one for cooling!

[PhilT]

1 hour ago, JohnMo said:

You can manage cycling but it doesn't generally happen out the box.

It's a shame ASHP manufacturers don't provide some kind of programmable "power level" control in addition to WC and fixed flow temp. Or even an option to simply prevent the ASHP from going below minimum power, with operation limited by room temp. That would at least be a step in the right direction.