ASHP with or without buffer tank? Or ST?

[Sailchick]

I’ve got a new build with wet UFH supplied by an 14Kw ASHP, we’re in the final stages of commissioning the whole thing. Despite being designed without a buffer tank, now our supplier is now recommending we install a buffer tank. I’m considering perhaps a Solar Thermal collector would be a better option? Any thoughts on this? 

[IanR]

There are pros and cons to a buffer, with a little more info we can help you identify them.

 

14kW is a relatively large heat pump for a new build, has this been purchased already?

 

How much energy do your energy loss calcs suggest is required to keep the temp stable in the house on a cold day? 

 

What heat emitters are planned and what flow temp is the system designed for? 

 

What size of UVC have you opted for and what occupancy level is the system designed for.

 

Do you have space for a large buffer, say, up to 200l?

 

Re. Solar Thermal, it is likely better to go with Solar PV with a diverter to an immersion, unless you are restricted on roof space. 

Edited March 26, 2023 by IanR

[Marvin]

Hi @Sailchick

 

If you live in Malta you will have different weather to the UK. With low temperatures typically averaging 9C in December, January I'm surprised you require such a large ASHP. However this could be due to very poor insulation or summer cooling requirement.

 

A buffer tank is usually used to store a volume of water to help the heating system work properly and a Solar collector is usually used to supply water heated by the sun to heat up a tank full for hot water use . In the UK one does not work the same as the other.

 

Malta has between 50 and 100% more sun a year than England, with an average of 5 hours a day in December (something unheard of in England!)

 

I would have thought a solar collector supplying all the heat for your hot water was a given (everyone would have one installed in Malta??)

 

However this has nothing to do with a buffer tank which adds more volume of water to your heating system. A buffer tank is often used when there are several zones of heating pipework individually turned off and on which reduce the available water to heat passing through the ASHP. This can cause the ASHP to heat up and then stop, heat up and stop, and so on, in short succession (called cycling). In tests an ASHP is best run with times of heating up exceeding 10 minutes, ideally about 20 minutes??. If you only have a small amount of water running through the ASHP it could stop heating before reaching optimum efficiency costing you more money to run. The solution to this is to install a buffer tank that will hold more water increasing the amount  of water available. the buffer tank heats up (which takes longer because of the volume) and cools down slower for the same reason.

 

As @IanR comments, the decision making about a buffer tank is:

56 minutes ago, IanR said:

What heat emitters are planned and what flow temp is the system designed for? 

 

Good luck

 

Marvin.

[Canski]

I used to live in Malta and my house was typical of Maltese builds. Zero insulation, thick limestone walls and yes I had a solar collector for heating the hot water. It was red hot in Summer and luke warm in winter so exactly the opposite of what we needed. We had no heating and survived the winters with Gas heaters and extra clothing.  
 

Maltas main problem is that it gets so humid in winter and at 9 degrees in winter it feels bloody freezing inside the houses.  I remember reading the soggy newspaper on the terrace in the sunshine. These days many people have air to air heating my son has about 6 of the things around his house and I would hate to see his electric bill. He is due to carry out some major refurbs over the next few years so I will be interested to see how you get on. 

[IanR]

32 minutes ago, Marvin said:

If you live in Malta

 

Ah, good spot, Location doesn't show up on the phone...

[Sailchick]

2 hours ago, Canski said:

I used to live in Malta and my house was typical of Maltese builds. Zero insulation, thick limestone walls and yes I had a solar collector for heating the hot water. It was red hot in Summer and luke warm in winter so exactly the opposite of what we needed. We had no heating and survived the winters with Gas heaters and extra clothing.  
 

Maltas main problem is that it gets so humid in winter and at 9 degrees in winter it feels bloody freezing inside the houses.  I remember reading the soggy newspaper on the terrace in the sunshine. These days many people have air to air heating my son has about 6 of the things around his house and I would hate to see his electric bill. He is due to carry out some major refurbs over the next few years so I will be interested to see how you get on. 

Absolutely correct! But since ours is a new build we’ve heavily insulated our house and used bricks for the internal skin. In summer we have ceiling fans, house is very well ventilated and will use supplement with the Air Conditioners. Yup electricity bills are extortionate, which is why we went for UFH in the winter opposed to the air heating. 

[Canski]

Sailchick. Well done you ! It’s good to see somebody making an obvious change. I visit Malta about 5 times a year and am amazed that not much has been updated in construction. 
 

can I ask what insulation you have between your outer skin and inner skin of blocks ? 

When I finished my shell there back in the 90’s there were no flat packed kitchens available. It took 2 and a half years for my local carpenter to build the kitchen. 

[Sailchick]

3 hours ago, IanR said:

There are pros and cons to a buffer, with a little more info we can help you identify them.

 

14kW is a relatively large heat pump for a new build, has this been purchased already?

 

How much energy do your energy loss calcs suggest is required to keep the temp stable in the house on a cold day? 

 

What heat emitters are planned and what flow temp is the system designed for? 

 

What size of UVC have you opted for and what occupancy level is the system designed for.

 

Do you have space for a large buffer, say, up to 200l?

 

Re. Solar Thermal, it is likely better to go with Solar PV with a diverter to an immersion, unless you are restricted on roof space. 

Thanks so much for your valuable input. It’s a large residential house, with a home office. Occupancy roughly 4 person. Yes, the heat pump has already been purchased. We aren’t restricted with roof space. 
 

I don’t have the calculations at hand I’d have to ask the supplier. Yes we are in Malta, which I would say our winter matches UK’s summer plus humidity. 

 

4 hours ago, IanR said:

There are pros and cons to a buffer, with a little more info we can help you identify them.

 

14kW is a relatively large heat pump for a new build, has this been purchased already?

 

How much energy do your energy loss calcs suggest is required to keep the temp stable in the house on a cold day? 

 

What heat emitters are planned and what flow temp is the system designed for? 

 

What size of UVC have you opted for and what occupancy level is the system designed for.

 

Do you have space for a large buffer, say, up to 200l?

 

Re. Solar Thermal, it is likely better to go with Solar PV with a diverter to an immersion, unless you are restricted on roof space. 

 

[Sailchick]

49 minutes ago, Canski said:

can I ask what insulation you have between your outer skin and inner skin of blocks ? 

Thanks! I’ve tried but the country is so backwards, the architect laughed at me when I told him I wanted to put in insulation. We used high density polystyrene boards. 
re kitchens, they have advanced 

[joth]

Not sure it's been mentioned but the design will also depend on the heat pump make/model. If it's a basic one with little to no modulation (maybe not even inverter driven?) then a buffer tank is much more likely to be needed. 

 

Also in Malta I think PV makes much more sense than ST and you can use PV for cooling, and to drive DHW heating via the heat pump can be a good choice depending what you're paid for energy export vs import

 

Edited March 26, 2023 by joth

[Marvin]

46 minutes ago, joth said:

Also in Malta I think PV makes much more sense than ST and you can use PV for cooling, and to drive DHW heating via the heat pump can be a good choice depending what you're paid for energy export vs import

+1 having read @Canski's reply.

[Canski]

2 hours ago, Sailchick said:

Thanks! I’ve tried but the country is so backwards, the architect laughed at me when I told him I wanted to put in insulation. We used high density polystyrene boards. 
re kitchens, they have advanced 

I don't think it's backwards but it can be hard work. Yes kitchens and bathrooms are much easier to source. It must be much easier now. My son works in Big Matt at Ta Qali. There was nothing like that there back in the day. 

[Sailchick]

1 hour ago, Canski said:

I don't think it's backwards but it can be hard work. Yes kitchens and bathrooms are much easier to source. It must be much easier now. My son works in Big Matt at Ta Qali. There was nothing like that there back in the day. 

Yes places like big Mat are great!