Cooling to Complement Radiator Central Heating in New Build Design

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#3027953 27-Jan-2023 16:52

Handle9:
tweake:

if your want good active cooling then you need to build the house for that.

Nah, you just need enough capacity. It’ll be expensive to run but you can overcome a lot with enough kW.

maybe i should have said "efficient" cooling rather than "good".

big part of it is how do you run the house. if its run with excessive ventilation then you need bigger aircon, but then if you run the house properly the aircon is oversized. you just end up with poor performance because it can't work both ways.

tweake

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#3027955 27-Jan-2023 16:54

Handle9:
nickb800: Can you get away with some good ol fashioned ceiling fans? Would help to avoid the capital cost of two heating systems.

We have ceiling fans for summer cooling, find they have low capital cost, minimal running cost, and work really well (as long as you're underneath them)

Ceiling fans make a big difference and in my experience are effective up to 30 degrees. I’ve just installed them through my house which has ducted units.

If you are buying ceiling fans modern DC fans are much quieter, cheaper to run and more convenient than old school AC fans.

Saying that I tolerate heat now that I’ve been in the Middle East for over 4 years so take 30 degrees with a grain of salt. I’m freezing today and it’s 17 degrees outside.

+1 ceiling fans are great and highly recommended. really good for well designed houses or during minimal heating/cooling seasons where the heating/cooling system is not running enough to give good distribution of air.

larknz

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#3028020 27-Jan-2023 20:55

If the outside temperature is over 30 degrees you need active cooling, unless you have a very well designed house that is not going to let the outside heat in and will also handle the heat that is generated internally.

larknz

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#3028021 27-Jan-2023 20:58

Ceiling fans move hot air around. In my opinion they are good in winter, but not so good in summer.

tweake

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#3028026 27-Jan-2023 21:10

larknz: Ceiling fans move hot air around. In my opinion they are good in winter, but not so good in summer.

still good in summer if you have some cooling. it moves the air around so it can be cooled. especially if only doing small amount of cooling and aircon fan speed is low.

tweake

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#3028029 27-Jan-2023 21:21

larknz: If the outside temperature is over 30 degrees you need active cooling, unless you have a very well designed house that is not going to let the outside heat in and will also handle the heat that is generated internally.

any time the outside temp is near or above your desired temp, then you need active. last week temps here was 27c, thats not going to cool a house down to 22c.

insulation keeps heat in, as well as out. "internal" heat, assuming summer, is mostly from the sun. so managing window size, type and shade is important. very common to see excessive glass used and houses cook in summer. with high glass to wall ratios you also drop insulation value way down and increase costs.

then theres things like shading from trees, which is uncontrolled. trees grow, change size and shape, die and fall down. if its close enough for shade its possibly close enough to do damage to the house.

really old school and proven to be poor performing.

Handle9

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#3028030 27-Jan-2023 21:25

larknz: Ceiling fans move hot air around. In my opinion they are good in winter, but not so good in summer.

We are at the coldest part of the year here in the Middle East. It was 17 degrees today. Ceiling fans provide considerable impact on comfort (as opposed to temperature) until it gets to around 30. After that you need mechanical cooling but every day you don’t run your AC is a day you save money.

Modern DC ceiling fans are also considerably more pleasant to be around than mechanical cooling. They run almost silent.

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larknz

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#3028034 27-Jan-2023 21:34

If you are used to living with 27-30 degrees then a fan moving 30 degree air around might be acceptable. But if you are used to 20 degrees then it won't be acceptable. Especially as the temperature at ceiling height will be hotter than the air at the level you are sitting.
I have plenty of memories of lying in bed at night when the outside temperature was 30+ and the fan was no help at all.

Handle9

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#3028038 27-Jan-2023 21:46

larknz: If you are used to living with 27-30 degrees then a fan moving 30 degree air around might be acceptable. But if you are used to 20 degrees then it won't be acceptable. Especially as the temperature at ceiling height will be hotter than the air at the level you are sitting.
I have plenty of memories of lying in bed at night when the outside temperature was 30+ and the fan was no help at all.

How many days of 30+ do you have? If it's only a few days a year does that matter to you if you have a couple of uncomfortable nights?

In NZ you'll get more nights where fans make a difference to comfort than when you need AC. The level of investment and running costs are also considerably less. It depends what is important to you and where you want to invest.

larknz

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#3028040 27-Jan-2023 21:57

It all depends on your personal situation. I would rather have a/c than rely on a fan.

tweake

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#3028163 28-Jan-2023 10:05

my last place used to get very hot and having windows open and fans going did stuff all. sleeping was always rough.

this place the first heat pump went into the bedroom. finally a decent nights sleep. best thing ever.

cost wise is over blown. running costs are small. even for my place which is typical 80's with single glazing, running multiple heat pumps almost every day cost about $20 a month in summer. a modern properly insulated house the running cost is tiny.

timmmay

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#3028165 28-Jan-2023 10:10

I have a small Daikin heat pump in my home office. It's a little cool in the mornings, in the afternoon without cooling it would reach 28 degrees or maybe higher. So in summer I use maybe an hour of warming, not much, and 4-5 hours of cooling. The Daikin app reports most days I use between 0.5kwh and 1kwh, sometimes a little higher. That's about $0.16 per day, or $4 a month. Winter will be more , and a larger room would be more.

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#3029100 29-Jan-2023 23:32

Adding hydronic fan-coil units in addition to or in place of radiators could be an option, running off the same air-cooled heat pump chillers turned to cooling mode - this solves the condensation issue. They could also provide supplementary heat in winter. Price-wise I don't know how it would come out - you need extra, more complicated controls and valving.

Feeding hydronic heating systems with heat pumps is questionable and likely will not get you both the same experience as gas/coal-fired radiators, and the same running costs as air-to-air systems.

Conventional systems typically run with high water temperatures of ~70C, meaning that radiators can deliver a lot of heat per unit area and are hot. Heat pumps significantly reduce efficiency and capacity at these temperatures, often becoming little better than electric, especially at low outdoor temperatures - depends where you're building, but if you get snow, a -10 to 70C delta just isn't going to be practical.

Alternatively, you can add tons more radiator, underfloor, or fan-coils, allowing you to run water more around 40-50C. The radiators won't be as hot but efficiency will be much improved.

Thermal mass cureth a multitude of sins, and it's something that studs-and-gib construction really doesn't have much of. Add enough extra weight that you can heat during the day and coast at night, or cool at night (if at all) and coast during the day, and things will be much better.

Handle9

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#3029103 29-Jan-2023 23:45

The basic controls for a hydronic unit isn’t expensive. It’s a thermostat driving an on/off cooling valve with a fan speed selector. This is what most hotel rooms have.

If you want demand control for the heat pump needs more sophisticated gear. I wouldn’t bother with hydronics, the cost involved in insulated pipe work makes it prohibitive and it doesn’t work very well.

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#3029110 30-Jan-2023 00:33

Handle9: The basic controls for a hydronic unit isn’t expensive. It’s a thermostat driving an on/off cooling valve with a fan speed selector. This is what most hotel rooms have.

If you want demand control for the heat pump needs more sophisticated gear. I wouldn’t bother with hydronics, the cost involved in insulated pipe work makes it prohibitive and it doesn’t work very well.

Each fan-coil, sure. Thermostatic controls on radiators are even simpler. Mechanical thermostat operated by heat and adjustment knob opens/closes valve proportionally based on that.

Even the head-end controls for a straight heat/straight cool system aren't bad, especially if (as in lots of (older) commercial buildings), you don't really care about efficiency. Buffer tank, 24/7 circulating pump with bypass zone, thermostat on boiler/chiler, job done. Simultaneous heat/cool with four-pipe systems is easy, too - basically, you operate two separate systems and just open the valve you want in each location.

The issue is the extra controls for heat/cool switchover, if you run a two-pipe system. Determining whether to run in heating or cooling is the first question - the system needs to look ahead, not just at demand now. No point getting the system all warmed up and hot for half an hour on a summer morning, as the heat energy stored in a hydronic system is way more than in air-to-air. Complexes with this system often just go for 'summer mode' and 'winter mode' with a manual switchover, but that's not really feasible here unless you have tons of building thermal mass - we get hot-ish winter days and cold-ish summer days.

Do you adjust water temperature based on projected demand to improve efficiency? That's a load more optimisation.

Next, you need to reverse operation of all the thermostats so that they open when too hot, not when too cold. And possibly lock out or limit flow for non-condensate-safe zones like radiators, radiant floor etc. That's easy if manual and you're doing it twice a year, and just a bunch of code if it's all in a PLC, but with standalone thermostats it's going to be a pain and more conductors.

Do you stage multiple types of heating/cooling, e.g. in winter turn on the radiators first, then fan-coil if the rads can't keep up? In summer, it may be the opposite, with additional monitoring of humidity. Basic thermostats won't cope with this.

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