--- title: Using Mini Split Heat Pumps for Space and Hot Water Heating date: 2021-10-24T08:59:14+00:00 modified: 2023-02-19T19:49:04+00:00 image:: https://kaspars.net/wp-content/uploads/2021/10/mini-split-space-hot-water-heating.png permalink: https://kaspars.net/blog/mini-split-space-hot-water-heating post_type: post author: name: Kaspars avatar: https://reverse.kaspars.net/gravatar/avatar/92bfcd3a8c3a21a033a6484d32c25a40b113ec6891f674336081513d5c98ef76?s=96&d=mm&r=g post_tag: - Building Science category: - Electronics - Passive House --- # Using Mini Split Heat Pumps for Space and Hot Water Heating Mini split air conditioners are great little air-source heat pumps that can work in the reverse and provide heating to the building, too. For highly insulated houses built according to the [Passive House standard](https://passipedia.org/basics/building_physics_-_basics/heating_load) they technically provide enough power to support both space and hot water heating. Passive houses require a heating load of only 10W per square meter or 15kWh of total energy per square meter per year to condition the inside air. That means that technically a 100m2 house requires only a 1kW heater which can be easily served with the smallest mini split units on the market that have a total heating/cooling power of 3kW. Wouldn’t it be great if the remaining 2kW could be used for heating the hot water? However, such units are pretty much non-existent or they are way over-sized and expensive for the needs of a highly efficient house. So I’m starting a project to add an additional 3kW plate heat exchanger to the indoor gas/fluid line of the cheapest mini-split air conditioner with the heating functionality, to transfer the heat to another fluid loop passing through a 1m2 heat exchanger of a 100 liter hot water tank: ![Mini Split air conditioner for space and hot water heating](https://kaspars.net/wp-content/uploads/2021/10/mini-split-space-hot-water-heating.svg)Mini-split air conditioner heating another fluid loop through a plate heat exchanger (with bold outline) that is connected to a hot water tank.## Design Questions - Does it need a bypass for the plate heat exchanger to decouple the water tank from the air-con while the unit is in the cooling mode? Or is it sufficient to just turn off the circulation pump for the hot water tank heat exchanger? - What are the flow rates for the hot water tank heat exchanger loop with a 1m2 tank heat exchanger surface? ## Existing Solutions There are several air-source heat pumps that support hot water heating: - Gree Versati III - Daikin Altherma Note that none of them enable space heating via a refrigerant-to-air heat exchanger found in traditional mini splits. ## Proposed Components ### 1. Mini Split with Heating Support [Midea Blanc](https://mideauk.co.uk/products/blanc-series/), [AlpicAir Premium Pro](https://alpicair.com/en-gb/products/residential-air-conditioners/wall-mounted-split-systems/premium-pro-series), Gree Lomo Nordic or similar costing around EUR 500. Requires knowledge of the communications protocol with the outside unit to control the device without relying on the inside unit. I ended up getting the [Gree Amber Nordic GWH09YD-S6DBA1](https://kaspars.net/blog/gree-amber-nordic-gwh09yd-s6dba1) which works well down to -30℃ (-22℉). ### 2. Hot Water Tank with Heat Exchanger [Kospel SWK100](https://kospel.pl/en/products/76-cylinders/1348-swk-termo-top-2.html) hot water tank (around EUR 400) with an internal heat exchanger loop area of 1m2 or more. ### 3. Plate Heat Exchanger [Eko Air NB-238](http://www.ekoair.lv/en/Heat-exchangers/NB-EN/_NB-238/) brazed plate heat exchanger (around EUR 175) with support for 3MPa (30bar) pressure and 3/8″ SAE flare connectors for the gas line and G3/4″ connector for the water loop. The particular unit has a maxium float rate of 5 m3/h. ### 4. Circulation Pump for the Hot Water Heating [Wilo-Yonos PICO circulation pump](https://wilo.com/gb/en/Products-and-expertise/en/products-expertise/wilo-yonos-pico) (around EUR 130) with support for variable flow rate. Ideally with electronically adjustable flow rate. ### 5. Pipes, Expansion Tanks, Valves and Connectors TODO: List them all. ## Next Steps - ✅ Purchase Eko Air NB-238 heat exchanger with 30 plates. - ✅ Purchase and [reverse-engineer Gree Amber Nordic GWH09YD-S6DBA1](https://kaspars.net/blog/gree-amber-nordic-gwh09yd-s6dba1) air-source heat pump. - TODO: Calculate the heat exchanger area for the hot water tank to match the power of the heat-pump. Last updated: February 13, 2022. ## Suggested Reading - [Why air to water heat pumps are a market opportunity for hydronic professionals](https://www.hpacmag.com/tech-pulse/why-air-to-water-heat-pumps-are-a-market-opportunity-for-hydronic-professionals/) videos [part 1](https://www.youtube.com/watch?v=o_TjkyUuHeY) and [part 2](https://www.youtube.com/watch?v=PU3uy3PisbM) by John Siegenthaler. ## Existing Solutions ### AHUcom A few month after I started researching this idea, I found [AHUcom which does the following](http://gree.at/uploads/navody/gree_ahu_com_r410_1.03_defrost_users_manual_2019.pdf): > AHUcom electronic communication module allows you to connect GREE brand outdoor unit from U-Match Series 5 to any air handling units equipped with direct expansion air exchanger and drive it via any control system. The connection with the outdoor unit is happening via two wires labeled `A` and `B` and it is not clear if those used for pure RS485 or something custom. ### Daikin Multi+ (Multiplus) [Ed in the comments](#comment-330274) found [Daikin Multi+](https://www.daikin.eu/en_us/product-group/air-to-air-heat-pumps/multiplus.html) which has an indoor hot water tank (EKHWET-BV3, [installation manual PDF](https://kaspars.net/wp-content/uploads/2022/10/EKHWET-BV3-Installation-manual_4PEN680074-1B-english.pdf)) connected directly to the refrigerant loop of the outdoor unit along with number of mini-split indoor units.